1.1.1. The contents of episodic memory

Episodic memory shares many features with other capacities, such as imagination, dreaming, navigation, counterfactual thinking, and future planning (Addis et al. Reference Addis, Pan, Vu, Laiser and Schacter2009; Buckner & Carroll Reference Buckner and Carroll2006; De Brigard Reference De Brigard2014a; Hassabis et al. Reference Hassabis, Kumaran and Maguire2007a; Reference Hassabis, Kumaran, Vann and Maguire2007b; Schacter et al. Reference Schacter, Addis and Buckner2007; Spreng et al. Reference Spreng, Mar and Kim2009). The common denominator of all of these different capacities seems to be that they are subserved by a system that flexibly constructs richly contextualized scenarios on the basis of stored content (Hassabis & Maguire Reference Hassabis and Maguire2007; Reference Hassabis and Maguire2009). The neural substrate of this “scenario construction system” is localized in the medial temporal lobes, specifically in the hippocampus (Cheng et al. Reference Cheng, Werning and Suddendorf2016; Maguire & Mullally Reference Maguire and Mullally2013; Maguire et al. Reference Maguire, Intraub and Mullally2015). Constructed scenarios are thought to consist of simulations of events extended over time and space (Moser et al. Reference Moser, Kropff and Moser2008), and construction of a given scenario has been shown to activate the sensory cortex in a manner similar to the perception of that scenario (Wheeler et al. Reference Wheeler, Petersen and Buckner2000).

Crucially, however, scenario construction has to be distinguished from stored information (i.e., the memory trace), on the one hand, and episodic memory on the other. Although debate exists about what, exactly, memory traces should be taken to be (De Brigard Reference De Brigard2014b; Robins Reference Robins2016b), there is little disagreement that they are not identical to the outputs of the scenario construction system (Cheng et al. Reference Cheng, Werning and Suddendorf2016).Footnote ⁴ Instead, scenario construction enriches and recombines trace information depending on the function its output serves. Scenario construction subserves a range of different capacities, not just episodic memory: Imagination, dreaming, navigation, and planning make use of memory traces, too. All of these capacities are supported by our ability to store and retrieve information learned in specific situations in the past.

One way to understand the construction process in episodic memory retrieval is as a Bayesian inference with the aim to accurately reconstruct a past event on the basis of available evidence (De Brigard Reference De Brigard2012; 2014a; Hemmer & Steyvers Reference Hemmer and Steyvers2009). This evidence comes from the memory trace, on the one hand, and relevant semantic information on the other (Cheng et al. Reference Cheng, Werning and Suddendorf2016). Depending on the functional role a given construction will play, the construction process will then rely more or less heavily on the memory trace or semantic information. For example, the construction of a counterfactual or future-oriented scenario should rely less heavily on trace as compared to semantic information. Indeed, patients with semantic dementia have been found to be impaired in constructing event simulations about the future (Irish et al. Reference Irish, Addis, Hodges and Piguet2012a).

Some authors have proposed a radical constructivist view of episodic remembering, positing that memory traces essentially play no privileged role in the construction of the contents of episodic memory (e.g., Michaelian Reference Michaelian2016a). Instead, these authors argued that there is no difference between inferences involved in the construction of factual and counterfactual scenarios (De Brigard Reference De Brigard2014a). However, as Robins (Reference Robins2016a) has argued, based on an analysis of common memory errors (such as the famous Deese-Roediger-McDermott [DRM] effect; Roediger & McDermott Reference Roediger and McDermott1995), episodic memory construction cannot be entirely independent of memory traces. Robins argues that such memory errors can occur only because some information has been retained. Thus, although it seems likely that the construction process does not have to rely on trace information, it will commonly take trace information into account. In particular, there must be differences in the way construction processes make use of stored information depending on whether the function of the construction is to represent an actual or possible occurrence. That is, in constructing a scenario representing an actual past event, the construction process should assign a privileged role to the memory trace in assigning probabilities to different priors.

The contents of episodic memory are, then, the outputs of a scenario construction mechanism. Such constructions would qualify as “minimal” episodic memory: They are quasi-experiential in the sense of including spatiotemporal context, perspectivity, and modality-specific sensory information. Scenario construction could then be taken to be sufficient for the representation of specific past events.

1.1.2. The format of episodic memory

Scenario construction alone is, however, not sufficient for episodic memory to occur: Hippocampus-based constructions become episodic memories only when they are conceptualized in a certain way, namely, as the outcome of past first-person experience. The event construction itself does not seem to differentiate between imagined and remembered scenarios. For this reason, some authors have proposed that autonoesis serves as a “memory index”: a representational tag differentiating episodic memories from imaginations (Klein Reference Klein2014; Michaelian Reference Michaelian2016a). In this view, the difference between imagined and remembered scenarios equates to the difference between factual and counterfactual event representations. Autonoesis would then allow us to differentiate between factual and counterfactual representations. However, if the content of autonoesis is indeed a proposition to the effect of “I had these experiences,” it alone cannot differentiate counterfactual from factual event representations. Instead, autonoesis marks those events of which one had firsthand experience as opposed to some other source.

To see this, note that both remembering and imagining a particular past event are compatible with the belief that the event indeed occurred. One can (even accurately) imagine a past event that one believes to have occurred. This is, in fact, common when we represent events of which we have only secondhand information (see also Pillemer et al. Reference Pillemer, Steiner, Kuwabara, Kirkegaard Thomsen and Svob2015). Thus, although autonoesis does indeed serve as a memory index, it does so by effectively distinguishing event representations according to their source. Further, if autonoesis is not part of the content of the construction, it must be an outcome of second-order processes specific to episodic memory occurring at retrieval (Klein Reference Klein2013b; Klein & Markowitsch Reference Klein and Markowitsch2015; Wheeler et al. Reference Wheeler, Stuss and Tulving1997). The mechanisms of episodic retrieval have long been a neglected area of memory research (Roediger Reference Roediger and Tulving2001). An exception to this has been the “source-monitoring framework” by Johnson and colleagues (Johnson & Raye Reference Johnson and Raye1981; Johnson et al. Reference Johnson, Hashtroudi and Lindsay1993). These authors have argued that episodic retrieval involves monitoring processes that determine the source of retrieved information. According to Johnson (Reference Johnson2005), episodic memory is in fact nothing but source memory.Footnote ⁵

A similar perspective has been proposed by Cosmides and Tooby (Reference Cosmides, Tooby and Sperber2000; see also Klein et al. Reference Klein, German, Cosmides and Gabriel2004), who argued that the appropriate functional role that a given output of scenario construction ought to play in inference is dependent on its source. This, in turn, necessitates that the contents of the construction be representationally decoupled from their direct relationship to reality. This is accomplished by applying a source tag to these contents, which governs how they can be further used in inference. Indeed, source-monitoring mechanisms seem to fill the role of such decoupling processes; they effectively endorse contents under a given description (Michaelian Reference Michaelian2012a; Reference Michaelian2012b).

This process, Cosmides and Tooby (Reference Cosmides, Tooby and Sperber2000) argued, is best described as the application of an appropriate epistemic attitude.Footnote ⁶ In the case of episodic memory, the attitude of remembering corresponds roughly to the proposition “has been obtained through firsthand informational access.” Cosmides and Tooby went on to propose similar attitudes for imagination, planning, and so forth. Of course, attitudes cannot be indiscriminately applied to any content; for example, one cannot remember a future event. However, this proposal makes sense of the fact that the same simulation of a specific past event can both be remembered and imagined. Moreover, because attitudes can be recursively embedded, this view can accommodate the fact that we can (for example) remember imagining. In effect, the processes involved in source monitoring can thus be described as resting on a complex metarepresentational grammar, in which different attitudes, each with their own epistemic status, can be embedded within each other to establish the epistemic status of the construction as a whole.

Crucially, this view preserves the strengths of the minimal view of episodic memory (Russell & Hanna Reference Russell and Hanna2012) in accounting for the distinctive phenomenology involved, while also accommodating the intuition underlying self-reflexive views, according to which episodic content is not enough for episodic memory to occur (Klein Reference Klein2013b). Autonoesis is here taken to be an outcome of the capacity to metarepresentationally embed outputs of the scenario construction system under the epistemic attitude of remembering.

1.1.3. Event memory and episodic memory

Hippocampus-based event constructions do not have to be embedded under a metarepresentational attitude in order to support behavioral decisions. This at least is suggested by findings showing that the hippocampus is implicated in implicit memory tasks (Hannula & Greene Reference Hannula and Greene2012; Olsen et al. Reference Olsen, Moses, Riggs and Ryan2012; Sheldon & Moscovitch Reference Sheldon and Moscovitch2010). That is, scenarios of specific past events can be represented as having occurred without the attitude of remembering being applied.

Note that believing is an epistemic attitude as well, albeit one that does not necessarily require the metarepresentation of its contents. Arguably, we adopt the attitude of believing to semantic memories by default. Thus, if the same attitude is applied to constructed scenarios, we should expect their content to acquire inferential properties similar to semantic information. However, although they do not differ in content (they are about specific past events), believed event simulations are not episodic memories.

Instead, we reserve the term event memory for this kind of representation (for similar proposals, see Keven Reference Keven2016b; Rubin & Umanath Reference Rubin and Umanath2015). Such event memories might differ from full-blown episodic memories in that they include source information only in the sense of allowing the distinction among different events (Crystal et al. Reference Crystal, Alford, Zhou and Hohmann2013), are not located in subjective time (Nysberg et al. Reference Nysberg, Kim, Habib, Levine and Tulving2010), are not necessarily subject to conscious awareness (Dew & Cabeza Reference Dew and Cabeza2011; Hannula & Ranganath Reference Hannula and Ranganath2008; Henke Reference Henke2010; Moscovitch Reference Moscovitch2008), are not self-referential (Rubin & Umanath Reference Rubin and Umanath2015), and do not have “narrative structure” (Keven Reference Keven2016b).

Such a distinction between event and episodic memory is at least tentatively supported by findings from several lines of research. Infants demonstrate some capacity for recalling events (Bauer & Leventon Reference Bauer and Leventon2013; Mullally & Maguire Reference Mullally and Maguire2014), but only between the ages of three and five years do children begin to access event information as the source of their beliefs (Haigh & Robinson Reference Haigh and Robinson2009). Moreover, the outputs of the hippocampus are not necessarily conscious (Henke Reference Henke2010), but nonetheless inform eye-movement behavior in implicit memory tasks (Hannula & Ranganath Reference Hannula and Ranganath2008). In fact, eye movements can serve as an implicit, veridical index of event memory, which can dissociate from explicit responses (e.g., Hannula et al. Reference Hannula, Baym, Warren and Cohen2012). On the side of neuropsychology, the case of RB mentioned above demonstrates that it is possible to lose the capacity to remember events autonoetically without losing the ability to access event information as such (Klein & Nichols Reference Klein and Nichols2012).

The concept of event memory thus allows us to take seriously the mnemonic abilities of young children (e.g., Burns et al. Reference Burns, Russell and Russell2015; Clayton & Russell Reference Clayton and Russell2009; Fivush & Bauer Reference Fivush, Bauer and Mace2010) and nonhuman animals (e.g., Corballis Reference Corballis2013; Clayton & Dickinson Reference Clayton and Dickinson1998; Gupta et al. Reference Gupta, van der Meer, Touretzky and Redish2010; Martin-Ordas et al. Reference Martin-Ordas, Haun, Colmenares and Call2010; Reference Martin-Ordas, Berntsen and Call2013; Templer & Hampton Reference Templer and Hampton2013) without necessarily attributing to them capabilities for episodic memory in the same sense as human adults possess them (Redshaw Reference Redshaw2014; Tulving Reference Tulving, Terrace and Metcalfe2005). Thus, event memory most likely differs in function from episodic memory, and we will focus here on a functional explanation for the latter.

1.2.1. Epistemic generativity

Crucially, when we remember, we do not simply generate two representations: a belief that the event in question happened and an episodic memory of the event. Instead, these representations are inferentially connected: We take ourselves to have knowledge about the event in question because we had firsthand access to it. Perner and Ruffman (Reference Perner and Ruffman1995), followed by Suddendorf and Corballis (Reference Suddendorf and Corballis1997; Reference Suddendorf and Corballis2007), took this circumstance to imply that episodic memory requires a form of causal understanding: namely, the capacity to understand that informational access leads to knowledge or belief. They tested this idea by investigating whether there is a correlation between children's episodic memory ability and their ability to infer “knowing” from “seeing.” Notwithstanding that Perner and Ruffman did indeed find such a correlation, it seems to us that what is involved in episodic memory is not only a capacity to infer knowing from seeing, but also the ability to further represent the sources of one's own present beliefs as sources in the first place (Haigh & Robinson Reference Haigh and Robinson2009).

As we have argued above, episodic memory in some sense is just a specific type of source memory. When we remember, the content of the memory no longer functions as an event representation but instead as the source of a present belief. Representing the source of a belief requires, but importantly goes beyond, the inferences involved in ascribing knowledge or belief on the basis of informational access. In the latter case, one simply takes note of the fact that a given agent has appropriate informational access to X and, from this circumstance, infers that she now knows X. From the fact that Anna has looked inside the box, Ahmed infers that she knows what is inside it. In the former case, however, one has to additionally represent the inferential relationship holding between the episode of informational access and the knowledge state. In this case, from the fact that Anna looked inside the box, Ahmed infers not only that she now knows what is inside, but also that this is so because she has seen it.

In other words, to represent the source of a given belief requires the representation of the kind of justification that this belief has received. Therefore, in our account, the represented relation between a given past episode of informational access and a given present belief is one of justification. Episodic memory requires the capacity to understand not only that seeing leads to knowing, but further that seeing justifies claims to knowledge.

Another way to frame the distinction between episodic memory, event memory, and semantic memory would thus be according to their respective role in belief formation: In contrast to event memories and semantic memories, episodic memories are not beliefs but, rather, provide grounds for believing. In more technical terms, event memory and semantic memory are epistemically preservative: They preserve the original justification of the endorsement of their contents through time. In contrast, episodic memory is epistemically generative Footnote ⁷ : It generates present justification for why we should endorse its contents (Burge Reference Burge1993; Dokic Reference Dokic, Hoerl and McCormack2001; Matthen Reference Matthen2010). When we remember a given event, the fact that we remember supports our belief that this event indeed occurred insofar as it provides a reason for this belief (Teroni Reference Teroni and Reboul2014; see also Audi Reference Audi1995). If you episodically remember that you were walking on the Red Square last August, you believe that this is indeed what you did simply because you remember it. Other types of memory, in this conception, are different exactly because they do not include a justification of their own contents. When we retrieve information non-episodically, we “just know” without also “knowing why we know.”Footnote ⁸

1.2.2. Memory-belief congruency

Remembering and believing thus stand in a relation of justification in which the fact that we remember justifies our beliefs about past events. If this is the case, we might expect the contents of episodic memory to be largely veridical so as to provide normatively appropriate, reliable grounds for our beliefs. In particular, we should not expect our beliefs themselves to have any influence on what we remember.

As illustrated by Neisser's (Reference Neisser1981) famous case study of the memory of John Dean, the question of what it means for a memory to be veridical is not a straightforward one. Dean, a former counsel to president Richard Nixon during the Watergate affair, provided testimony that was usually in essence correct but contained many (mostly self-serving) incorrect details. In fact, whether a given memory should be described as veridical might depend on the method used for assessing it (Koriat & Goldsmith Reference Koriat and Goldsmith1996a). Consequently, although episodic memory is usually reliably veridical under some descriptions, there has also been a long tradition of research pointing out the fallibility of this system. Starting with Bartlett's (Reference Bartlett1932) classic treatment, an impressive amount of evidence suggests that the construction process on which episodic memory relies is surprisingly error-prone. Both encoding and retrieval processes typically alter information substantially (e.g., Alba & Hasher Reference Alba and Hasher1983; Roediger Reference Roediger1996; Schacter Reference Schacter2001). Crucially, one important line of evidence suggests that beliefs play an unexpectedly large role in the construction of episodic memories (Conway Reference Conway2005; Ross Reference Ross1989; Blank Reference Blank2009). In many situations, construction seems to be guided by one's current beliefs about whatever is to be remembered rather than the memory trace itself. If the construction process underlying episodic memory were indeed optimized to support beliefs about actual occurrences, such a trade-off would be unexpected.

Evidence for top-down influences on episodic memory comes from a range of experiments investigating the effects of post hoc manipulation of participants' attitudes, expectations, or appraisals on their memories. It is usually found in these studies that people remember the past inaccurately but congruent with, and supportive of, their newly acquired beliefs. For example, in a study by Henkel & Mather (Reference Henkel and Mather2007), participants were asked to make a choice between two options, each of which had an equal amount of positive and negative features associated with it. When asked to remember their choice later, however, participants misremembered the features of the options they chose as more positive than they were (see also Benney & Henkel Reference Benney and Henkel2006; Mather & Johnson Reference Mather and Johnson2000; Mather et al. Reference Mather, Shafir and Johnson2000; Reference Mather, Shafir and Johnson2003). Crucially, this shift was dependent on what participants believed they had chosen, irrespective of their actual choice (see also Pärnamets et al. Reference Pärnamets, Hall, Johansson, Noelle, Dale, Warlaumont, Yoshimi, Matlock, Jennings and Maglio2015). That is, here participants remembered having made a choice they did not actually make (but believed they did) and, additionally, remembered the option they believed they had chosen as having had more positive features than it actually did. In other words, they displayed both memory congruency with the induced belief and a memory distortion supporting this belief.

Similar congruency effects have been found in such diverse domains as memory for emotions (Levine Reference Levine1997), attitudes (Goethals & Reckman Reference Goethals and Reckman1973; Rodriguez & Strange Reference Rodriguez and Strange2015), one's own behaviors (Ross et al. Reference Ross, McFarland and Fletcher1981; Reference Ross, McFarland, Conway and Zanna1983), one's own traits (Santioso et al. Reference Santioso, Fong and Kunda1990), and even one's own clinical symptoms (Merckelbach et al. Reference Merckelbach, Jelicic and Pieters2010; Reference Merckelbach, Jelicic and Pieters2011). The methods of these studies are diverse, and it is, therefore, unclear to what extent each of these effects is specific to episodic memory. Evidence suggesting such specificity, however, is supplied by research on memory manipulation.

There is an impressive literature showing that it is possible to induce in people vivid, detailed false memories, which are subjectively indistinguishable from accurate recollections (Lampinen et al. Reference Lampinen, Neuschatz and Payne1997; Payne et al. Reference Payne, Elie, Blackwell and Neuschatz1996). People usually create false or altered memories in response to having changed their beliefs about a given event. This in turn is usually the outcome of having been exposed to persuasive communication (Nash et al. Reference Nash, Wheeler and Hope2015). In fact, persuasion is a main factor in the effectiveness of most memory manipulation paradigms (Leding Reference Leding2012). This suggests that induced beliefs can guide constructive retrieval.

On the basis of evidence about such belief-memory congruency effects, it seems fair to conclude that retrieval has a tendency to confirm prior beliefs rather than to contradict them. Such evidence then is not easily reconcilable with a view that takes episodic memory to be exclusively aimed at reconstructing events in the way they actually occurred. Rather, these studies show that the episodic construction process seems to just as often be geared toward constructing event representations so as to be consistent with, and supportive of, our prior beliefs. Commonsensically, we would assume episodic memory to be an exclusively belief-forming system. Phenomenologically, it seems to us that we form beliefs about the past on the basis of remembering it, not vice versa. In contrast, research on memory illusions suggests that beliefs about the past and episodic memory are reciprocally interconnected: Sometimes we remember an event because we believe it occurred.Footnote ⁹ And in turn, once we have constructed a memory on the basis of such a belief, the memory itself might serve to strengthen the belief that induced it.

Crucially, this does not mean that episodic memory is not commonly veridical. In fact, the effects of prior beliefs and attitudes on subsequent memory seem to be highly context dependent (e.g., Eagly et al. Reference Eagly, Kulesa, Chen and Chaiken2001). Veridicality in episodic memory construction is not an all-or-nothing affair. Instead, retrieval processes seem to aim to strike a balance between congruency with memory traces, on the one hand, and belief justification on the other. However, such a balancing act is not always possible. In some such cases, then, remembering an event will lead to belief revision, whereas, in others, believing that an event occurred will lead to the construction of an event simulation without a corresponding trace.

2.1.1. Mental time travel and constructiveness

This view is usually presented as having the advantage of being able to explain the constructive character of episodic memory: Imagining the future requires flexible recombination of stored event information. Given that, in this view, selection of this system has been driven by the future-directed aspect, the past-directed counterpart must be similarly constructive. This line of reasoning is thereby thought to explain the myriad ways in which our reconstructions of the past are error-prone: Selection has simply not optimized this system to represent the past accurately.

This account of constructiveness is, however, problematic, because it leaves us without an explanation for why we should ever be able to reliably and veridically recall past events. If evolutionary selection merely constrained our ability to mentally travel in time insofar as it was useful for simulating the future, remembering the actual past should be accidental. The future is not just a replay of the past, and to assume so would leave us unable to predict events based on new contingencies. We take it that the volatility of the future is exactly why this account is attractive as an explanation of the constructiveness of episodic memory. Episodic memory is, however, also reliably veridical in many cases; a fact that becomes mysterious in this view.

2.1.2. Remembering the future

One might posit that recollection of the actual past would be helpful for imagining the future: Our simulations of the future could be enhanced if we remembered the past first (Szupnar & McDermott Reference Szpunar and McDermott2008a). Selection then might have ensured veridicality in episodic memory because of the benefits an accurate representation of the past provides for our understanding of the future. To be sure, in order to imagine the future, it is important to retain information learned in the past because this will highly constrain any inference as to what might happen in the future. However, it is not clear what re-experiencing the past episodically does for simulating the future, or how it would contribute more to future planning than what semantic memory, extracted from past experience, could supply. As emphasized above, episodic memory is not identical to stored information, and mentally traveling back to the past will not itself include any information about the future.

In fact, if past- and future-directed mental time travel operate over the same type of content and merely differ in the temporal orientation they assign to their constructions, it is not clear why one would need the past-directed aspect at all to imagine the future. To see this, note that inferring what might happen in the future on the basis of an episodic memory is not the same as mentally traveling into the future in the sense required here. Suppose that, the last time you were at the swimming pool, there was a long line at the entrance. When planning to go to the swimming pool the next time, you might recollect this fact episodically and infer from this that there will likely be a long line again this time. Future-oriented mental time travel, however, is not the outcome of an explicit inference of this kind. Instead, in this case, when you ask yourself whether you should go to the swimming pool today, you might imagine that there will be a long line. Of course, the reason that this piece of information might be included in your imagination of this scenario might lie in the fact that there was a long line last time you were there, and you might even be able to infer this from your imagination. Crucially, however, there is no need for you to represent this when constructing your future swimming pool scenario.

It is thus telling that past- and future-directed mental time travel can be dissociated in episodic amnesia (Maguire et al. Reference Maguire, Vargha-Khadem and Hassabis2010; Schacter et al. Reference Schacter, Addis, Hassabis, Martin, Spreng and Szpunar2012). The loss of the capacity for episodic memory alone does not significantly impair people's ability to draw inferences about the future. Episodic amnesiacs are not stuck in time: They understand what the future is (Craver et al. Reference Craver, Kwan, Steindam and Rosenbaum2014b), can make future-regarding decisions (Craver et al. Reference Craver, Cova, Green, Myerson, Rosenbaum, Kwan and Bourgeois-Gironde2014a), and show normal discounting of future rewards (Kwan et al. Reference Kwan, Craver, Green, Myerson, Boyer and Rosenbaum2012). The claim that we can remember the past in order to imagine the future, then, seems unlikely to be true.

3.1.1. Remembering as a reason for others

But how could the fact that one remembers serve as a reason for others to believe a given assertion? Note that, in cases where minimal mutual trust between interlocutors can be assumed, it is indeed the case that “remembering” is generally taken by others to be a reason for accepting certain claims. Consider the following situation: John and Jenny are on a walk when Jenny expresses that she is worried that they might have left on the oven at home. To this John replies, “Don't worry, I remember that we turned it off.” Why should the statement that John remembers here be any more reassuring than simply stating: “Don't worry, we turned it off”? Here, “I remember” serves as a reason for Jenny to accept John's statement just as it serves as a reason for John to indeed believe that the oven was turned off.

Now, clearly remembering does not work as a reason here in the same way as an argument does. Instead, we can get a clearer sense of the work such autonoetic claims do in interlocution by taking a closer look at the pragmatic structure of testimony. Testimony entitles an interlocutor to take whatever is conveyed as true on the authority of the speaker. This entails that by giving testimony, the speaker herself has to take responsibility for the truth of whatever is stated (Brandom Reference Brandom1983; McMyler Reference McMyler2007; Turri Reference Turri2011). In the case of secondhand testimony, one can defer this responsibility, but only insofar as one can actually access the source of the information in question.

Indeed, Nagel (Reference Nagel2015) has recently argued that our propensity to represent the ways in which our epistemic states are grounded through source monitoring relates exactly to this circumstance. She observes that the different sources of belief we intuitively take to hold epistemic warrant do not regularly coincide with actual differences in reliability: An expert judgment received through testimony, for example, might well be more reliable than what one has concluded on the basis of one's own perception. It thus seems unlikely that source monitoring would serve a purely epistemic function. Instead, Nagel observed, “source monitoring matters when we need to communicate our judgments to others: indeed, even to decide what does and does not need to be conveyed, it matters where our judgments are coming from, and where our evidence is situated, relative to ourselves and our audience” (p. 301). In fact, the ubiquity with which source information is useful in communication has arguably led to its grammaticalization in about one quarter of all known languages as evidential markers (Aikhenvald Reference Aikhenvald2004; Speas Reference Speas2008). The distinction between indirect and direct forms of evidence seems to be common to all evidential systems.

This begins to make sense of the question of why episodic recollection comes with a representation of its own origin. In this view, autonoesis is the capacity that enables us to distinguish between cases in which we can assert epistemic authority for our own testimony and cases in which we cannot. Note that even in cases where one defers to someone else, one will have to take responsibility for the very act of doing so. If Hanna tells you, “Mary told me that Mark was not at the party yesterday,” while Hanna does not take epistemic responsibility for whether Mark was indeed at said party, she does take responsibility for the fact that Mary told her that he was not.

One reason for why it is important to monitor which assertions we can commit to in discourse is reputational. If we discursively commit to, and thereby allow others to rely on, the truth of an assertion, we take responsibility for its truth, and thereby put our reputation as a reliable informant on the line. Thus, discursive commitment comes at a potential (direct or reputational) cost in case our message is found to be unreliable. For our interlocutors, the fact that we are willing to incur such a cost is a reason to believe us. Through this dynamic, as Vullioud et al. (Reference Vullioud, Clément, Scott-Phillips and Mercier2017) have recently argued, discursive commitment is a way to stabilize communication. Claims to remembering, then, do not offer a way of overcoming skepticism in the same way as argumentation proper does.Footnote ¹³ Instead, it is an issue of competence: Episodic memory allows us to signal to others that we indeed have epistemic authority on a certain matter, which in turn commits us to our message, and this should cause others to believe us.

In fact, it is hard to see how else one would argue about certain past events. When it comes to the past, sometimes epistemic authority is all we have to go on when deciding what to believe. Indeed, young children preferentially endorse the testimony of informants who had firsthand informational access (Terrier et al. Reference Terrier, Bernard, Mercier and Clément2016), and Castelain et al. (Reference Castelain, Bernard, Van der Henst and Mercier2015) showed that young Maya children are more likely to endorse the testimony of a source claiming to have epistemic authority (“The hen went this way because I have seen it”) over a source giving no reason, even when it conflicted with another cue usually governing such endorsement (power).

Of course, episodic memory is not the only device allowing us to regulate our communicative commitments. Markers of confidence seem to be another one (Vullioud et al. Reference Vullioud, Clément, Scott-Phillips and Mercier2017). Episodic memory is simply the mechanism specifically geared toward regulating communication about past events. Therefore, communicatively negotiating the past often becomes a matter of convincing one's interlocutor that one remembers: that is, that one has epistemic authority on the matter in question. Because remembering is such an effective way of asserting epistemic authority, it might be beneficial to attribute the origins of (at least certain types of) event information to our own experience in situations in which this would be communicatively useful. This might explain some occurrences of the famous misinformation effect (Loftus Reference Loftus2005). Here, witnesses have been found to persistently over-attribute misleading information acquired about an event after its occurrence (post-event misinformation) to their experience of this event. From the perspective we have proposed here, this might simply be the best way to make use of this information in appearing as a good witness. After all, if the participants in these studies believed the misinformation to be correct (as they seemed to do), they must have experienced the event in this manner, too.

Going further, this analysis also reveals a functional aspect of the fact that episodic recollections are often rich in contextual details. Although event memory should similarly be characterized by the availability of contextual details, these details play a functional role for communicative purposes in episodic memory. When we debate a past event, the fact that we can produce rich, detailed descriptions serves as evidence for others – as it does for ourselves, too (Johnson & Raye Reference Johnson and Raye1981) – to believe that we are indeed remembering (Bell & Loftus Reference Bell and Loftus1988; Reference Bell and Loftus1989). The reason for this effect of detail might be that contextual details (1) give one's interlocutor more leverage to detect potential inconsistencies and reduce vagueness (Kraut Reference Kraut1978), as well as (2) supply information that might potentially be independently verified. For example, information about the location and co-witnesses of an event makes it possible to potentially obtain evidence about the event that is not dependent on the testimony of one's immediate interlocutor. Such independent verification will, in practice, often not be carried out. Instead, it might be enough that an interlocutor is willing to make her account subject to such verification, which is taken as a reason to accept her testimony. Consequentially, contextual elements that, at least potentially, make verification possible might be more readily available in recollection simply because this information should allow one to be perceived as more convincing. When we argue about the past, we often do not contest whether the event in question happened, but rather in what way it did, and having access to contextual details is often crucial to establish which of multiple accounts of an event should be endorsed and what it should be taken to entail.

3.1.2. The consequences of discursive commitment.

Another prediction following from this account concerns the fact that once one has publicly committed to, and therefore taken epistemic responsibility for, the truth of a certain version of events through testimony, this should have subsequent consequences on how and what one remembers. On the one hand, after testimony, it becomes less important to recall the actual event. Instead, to uphold one's commitment, maximize believability, and avoid reputational damage through inconsistency, one should stick to one's own account to a certain extent. In cases where one's account of an event and the actual happenings diverge, one might thus subsequently remember the event in question in a way that supports one's report. A range of memory distortion effects occurring as a consequence of memory report suggests that this is indeed what happens. For example, Cochran et al. (Reference Cochran, Greenspan, Bogart and Loftus2016) investigated the effect of altering participants' memory reports on their memory for crime events. They found that participants often did not detect the changes to their reports and instead altered their memories to fit the manipulated reports. Tversky and Marsh (Reference Tversky and Marsh2000) found that the public stance one takes on a past event biases recall to emphasize details supporting one's claim (see Higgins & Rholes, [Reference Higgins and Rholes1978] and Greene [Reference Greene1981] for related effects). This stance, in turn, has been found to depend on one's particular audience (arguably serving both reputation management and making one's own memory report easier to accept for others), further altering memory (Echterhoff et al. Reference Echterhoff, Higgins, Kopietz and Groll2008; Reference Echterhoff, Lang, Krämer and Higgins2009b; Kopietz et al. Reference Kopietz, Echterhoff, Niemeier, Hellmann and Memon2009; Pasupathi et al. Reference Pasupathi, Stallworth and Murdoch1998). In effect, after having reported an event, people subsequently do not recall the original event but rather a version in line with their latest retelling of it (Marsh Reference Marsh2007).

The extent to which such distortions would be communicatively useful should be constrained by how skeptical and informed one's audience is. People should be sensitive to the costs of being found wrong, and appropriately adjust the extent to which they prioritize consistency with their own account over accuracy. Thus, the distorting effects of giving testimony might be mediated by how skeptical and informed one perceives one's audience to be. To our knowledge, this prediction has not been tested.

On the other hand, commitment to one's testimony should cause one to be less easily convinced of a different version of occurrences, given that this would undermine one's own epistemic authority. Indeed, participants' susceptibility to social influence has been found to depend on whether they had committed in one way or another to certain details of an event (Bregman & McAllister Reference Bregman and McAllister1982; Loftus Reference Loftus1977; Schooler et al. Reference Schooler, Foster and Loftus1988). The reason for this cannot be simply epistemic, because in general, participants have been shown to be quite ready to update their memories on the basis of others' testimony. Instead, our account suggests that participants in these studies became resistant to social influence in order to ensure their own believability.

3.1.3. Recollective my-side bias

Being able to convince others that we are indeed remembering is only important insofar as it helps us to convince them about what we are remembering. The contents of our memories are crucial for supporting certain conclusions over others when it comes to the interpretation of what a given event entails. Thus, if episodic memory indeed has the communicative function of appropriately asserting epistemic authority about the past, we should expect it to make content available in a way that supports our claims.

Mercier and Sperber (Reference Mercier and Sperber2011) have argued that because the production of reasons does not serve normative epistemic goals but is meant to convince others, it should primarily find reasons in favor of whatever we want to claim. Their view predicts the well-known my-side bias in reasoning: the human tendency to reason from conclusions to premises, and not vice versa as normatively required. By analogy, when we claim that episodic memory is crucial for persuading others of a particular version of the past, we should similarly expect such a bias in remembering: To be able to argue for our beliefs about a past event, our recollections should tend to support those beliefs instead of contradicting them.

Indeed, such a recollective my-side bias is instantiated through the way in which our beliefs guide the construction of memory content. Similar to confirmatory reasoning, belief-guided memory construction (reviewed in sect. 1.2.2) can be taken to be a version of the my-side bias to the extent that one constructs a memory justifying what one already believes to have happened. Understanding memory reconstruction as an instance of my-side bias for the purposes of persuasion can make sense of the surprising interplay between beliefs and memory content: The constructive process tends to retrospectively create memories confirming and supporting held beliefs and attitudes. From this perspective, such false memories are simply the results of an inherent tendency to justify our beliefs about the past to ourselves in order to be able to justify them toward others; they illustrate a functional feature, rather than a bug in, the mechanisms of episodic memory. Thus, inducing beliefs about the past in participants is followed by false memories, because once we have accepted a piece of information, justifiability is ensured through the construction of supporting memory content.

Of course, if we are correct, there should be limits to this form of my-side bias. If the costs of being found wrong are high, or our audience can monitor our assertions effectively, we ourselves should be more skeptical toward the outputs of our own construction system (i.e., put more effort into checking their consistency) and consequently be less likely to form a false memory.

3.1.4. Selective remembering and motivated forgetting

A similar analysis can be applied to phenomena described under the heading of “motivated forgetting” (Anderson & Hanslmayr Reference Anderson and Hanslmayr2014). Motivated forgetting describes a process by which selective or inhibited retrieval leads to forgetting of aspects of (or entire) events. People tend to selectively remember arguments in favor of an endorsed conclusion or attitude while forgetting counter-arguments against the same conclusion or attitude (Waldum & Sahakyan Reference Waldum and Sahakyan2012). This process has been shown to be especially prevalent in the domain of moral violations. In fact, memories of one's own moral violations are more likely to be forgotten than memories of one's own moral behavior, so that people sometimes seem to display a form of “unethical amnesia” of their past (Kouchaki & Gino Reference Kouchaki and Gino2016). In contrast, Bell et al. (Reference Bell, Schain and Echterhoff2014) have shown that memory for the cheating behavior of others is well remembered when it is associated with personal costs but easily forgotten when associated with personal benefits. These processes lead to the phenomenon of rose-colored memories, which emphasize one's own moral character. Given the importance of episodic memory for the communicative negotiation of the past, such effects are not surprising. Both on the individual (Kappes & Crockett Reference Kappes and Crockett2016) and the collective level (Coman et al. Reference Coman, Stone, Castano and Hirst2014), selective remembering and motivated forgetting serve communicative ends: Convincing oneself simply helps to convince others (von Hippel & Trivers Reference von Hippel and Trivers2011).

3.1.5. Remembering reasons

As we noted in section 1.1.2, taking remembering to be an attitude makes intelligible how one can remember imagining, believing, wanting, and so forth. In our view, this makes sense insofar as the process of retrieving reasons via introspection in many cases amounts to an attempt at remembering these reasons. To see this, consider Johansson et al.'s (Reference Johansson, Hall, Sikström and Olsson2005) famous choice blindness experiments (for a higher stakes example, see Hall et al. Reference Hall, Johansson and Strandberg2012). In a series of two-alternative, forced-choice trials, participants were asked to choose, between two faces, the one they found more attractive. After answering, participants were presented again with the chosen face and asked to explain why they had chosen this face. Crucially, in a certain proportion of trials, the experimenter switched the presented face by sleight of hand so that the participant was now presented with the face they had not chosen. In this situation, not only did a substantial number of participants not notice the change, but they also went on to give reasons for why they ostensibly had chosen the face presented to them. How did the participants come up with reasons for a choice they had not made in this situation? Clearly, they must have constructed these reasons on the fly in response to being asked to justify their choice. Crucially, however, because the participants did not notice that they were justifying a choice they had not made, they presumably believed that the reasons they gave were actually the reasons that had guided their (imagined) original choice. The only way, however, this is possible is if the participants sincerely believed that they remembered these reasons. This kind of post hoc generation of memories is often required when we genuinely give reasons for our behavior after the fact. In this way, the attitude of remembering is crucial to introspecting our own past reasons.

3.1.6. Source monitoring as self-directed epistemic vigilance

As mentioned above, epistemic vigilance and the mechanisms designed to disarm such vigilance are essentially two sides of the same coin. The easiest and most effective way to anticipate one's interlocutor's vigilance might be to exercise such vigilance against one's own assertions before uttering them. Source monitoring, as described by Johnson et al. (Reference Johnson, Hashtroudi and Lindsay1993), displays just such a structure. Michaelian (Reference Michaelian2012a; Reference Michaelian2012b) noted that source-monitoring mechanisms are endorsement devices: They decide to what extent we should believe the contents of our own recollections by scrutinizing them for their believability, just as others do when they hear our testimony. These endorsement mechanisms might then be one way in which we can gauge whether we should indeed commit to a certain claim about the past or not. Although Johnson et al. (Reference Johnson, Hashtroudi and Lindsay1993) seem to have assumed that source monitoring is purely epistemic in function and compulsory in event recall, it might well be that these processes are only applied in situations in which scrutiny is required: situations in which one expects to face a (skeptical) audience.Footnote ¹⁴

3.2.1. Source-directed epistemic vigilance

Similar to our account, researchers (Boyer Reference Boyer, Boyer and Wertsch2009; Cosmides & Tooby Reference Cosmides, Tooby and Sperber2000; Klein et al. 2002; Reference Klein, Cosmides, Gangi, Jackson, Tooby and Costable2009;) have emphasized the role of episodic memory in epistemic vigilance. In their view, the fact that humans so excessively rely on communicated information has necessitated a mechanism allowing us to adjust the truth value of our beliefs according to their source. To decide whether an interlocutor is trustworthy, or whether to re-evaluate such trust, it is necessary to have access to her past behavior in specific situations. When we learn new information about an interlocutor's reliability after the fact, it is important to have access to our interaction history with this specific person to be able to re-evaluate any pieces of information we might have received from her. The importance of source monitoring in such situations is showcased in misinformation studies, in which participants are able to recover their original event representation when they are informed of the deceptive character of the misinformation (Blank & Launay Reference Blank and Launay2014; Echterhoff et al. Reference Echterhoff, Hirst and Hussy2005; Oeberst & Blank Reference Oeberst and Blank2012). However, as evidenced by the mediocre effectiveness of most post-warnings, episodic memory seems to be rarely used in this way. Most of the time when we are informed that a given source is untrustworthy, we merely discount this source in the future. Nonetheless, as predicted by our account, encoding is mediated by epistemic vigilance toward the source of information: Misinformation and conformity effects are not automatic but rather depend on participants' evaluation of their own confidence and the reliability of the source of the presented information (Allan et al. Reference Allan, Midjord, Martin and Gabbert2012; French et al. Reference French, Garry and Mori2011; Gabbert et al. Reference Gabbert, Memon and Wright2007; Jaeger et al. Reference Jaeger, Lauris, Selmeczy and Dobbins2012; Lindsay & Johnson Reference Lindsay and Johnson1989). When participants have reason to doubt their own (Asefi & Garry Reference Asefi and Garry2003; Clifasefi et al. Reference Clifasefi, Garry, Harper, Sharman and Sutherland2007) or others' ability (Kwong See et al. Reference Kwong See, Wood and Hoffman2001) or trustworthiness (Dodd & Bradshaw Reference Dodd and Bradshaw1980), they refrain from memory update. In such cases, rather than simply updating their own event representations on the basis of others' testimony, participants encode it in a separate trace (Ludmer et al. Reference Ludmer, Edelson and Dudai2015).

3.2.2. Interpersonal reality monitoring

The two-sided nature of vigilance and counter-vigilance is illustrated in another aspect of recollection. In deciding whether someone is telling the truth in recounting the past, we usually try to determine whether our interlocutor is remembering or making up the contents of her testimony. Research in the tradition of the source-monitoring framework has investigated how we make this decision about ourselves through so-called reality-monitoring mechanisms (Johnson Reference Johnson, Prigatano and Schacter1991; Johnson & Raye Reference Johnson and Raye1998).

Apart from allowing us to determine whether we should take ourselves to be actually remembering, reality monitoring could play a role in making this decision about others, too. That is, to decide whether we are remembering or imagining a given event, we might use the same mechanisms that are charged with this decision when evaluating others' testimony. This is suggested to some degree by studies on interpersonal reality monitoring – the ability to judge whether other people's memories reflect real or imagined events (Johnson et al. Reference Johnson, Bush and Mitchell1998; Johnson & Suengas Reference Johnson and Suengas1989). These studies suggest that participants use the same criteria to evaluate their own memory content and others' memory accounts, and can display above-chance discrimination performance in such situations (Clark-Foos et al. Reference Clark-Foos, Brewer and Marsh2015). Note, however, that this is not a matter of detecting outright deception but rather one of deciding whether we should grant our interlocutor epistemic authority. In detecting deception, we likely use other mechanisms to assess others' intentions, which in turn might influence our reality-monitoring decisions.

3.2.3. Veridical recollection and epistemic vigilance

Viewing episodic memory as striking a balance between the productive and receptive sides of communication can make sense of the confusing interplay between veridicality and malleability, described in section 1.2.2. Similar to reasoning (Mercier & Sperber Reference Mercier and Sperber2011), the evolution of episodic memory should have been subject to an “arms race” between senders and receivers of communicated information about past events. Whereas senders have an interest in inducing in their audience a representation of the past that is to their benefit, receivers are interested in acquiring useful (i.e., true) information. Thus, the better senders should be at manipulating their audience's beliefs about the past to their own benefit, the better receivers should be at discerning true from misleading information. Both sides of this interaction therefore require the capacity to represent the past accurately.

On the one hand, if episodic memory were never true, it would not convince anyone.Footnote ¹⁵ Thus, speakers should be sensitive to how informed and skeptical their audience is and consequently be more careful about what they commit to (i.e., exert more effort in checking their own memory representation for its believability). Receivers, on the other hand, should be sensitive to the interlocutor's intentions and (if available) spend more cognitive resources to monitor the believability of her utterances.

Thus, the epistemic vigilance functions of episodic memory coincide with the epistemic route from memory content to belief: We are able to form and revise beliefs on the basis of episodic recollection because this enables us to guard against others' incompetence and deceptive intent in communicative interaction. This perspective then gives us an explanation for why (and when) we should expect episodic memory to be veridical: Epistemic vigilance requires sensitivity to the actual past to enable us to review others' claims and decide when to revise our own beliefs on the basis of such claims. Moreover, the fact that we can expect others to be vigilant, and as such sensitive to the truth, should force us to stick to actual events to the extent that others can monitor us in communicative interaction. Thus, the construction process in episodic memory should be sensitive to the communicative situation we find ourselves in. In cases in which we face a skeptical audience, which raises the costs of being found unreliable, or when we are scrutinizing someone else's claims on the basis of our own memory, construction should aim at accurate event representation.

3.4.1. Remembering events generating social commitments

Because knowledge about specific events can be critical in assessing the truth of certain generalizations, their recollection can also be crucial in supporting the communicative assertion of many such generalizations (“I remember seeing him beating his wife, therefore he must be an aggressive person”). In principle, any inductively derived conclusion can be supported or undermined by pointing to specific events. Nonetheless, reference to past events is not mandatory in arguing for inductive generalizations. In principle, one can argue for such assertions by pointing to other generalizations one holds true as well.

There are, however, certain claims for which it is impossible to argue except by reference to specific past events: namely, the assertion of social commitments. Examples of such events are agreements between multiple parties that commit one or the other interactant to a certain behavior in the future (Schelling Reference Schelling1960). But these are by no means the only examples; potentially, any event can be used to establish social commitments or entitlements depending on what interpretation one chooses after the fact. Indeed, most events that happen to us on a daily basis are heavily loaded with social meaning, which largely depends on their potential to ground such social commitments. And this potential is, in turn, realized only when a case can be made that a given event did indeed occur in a specific way in the past. In fact, sometimes this is the only way to argue for many present entitlements.

The acts through which we engage in and negotiate our social commitments are causal events: Their effect is the establishment of a “social fact.” However, in contrast to causal events that result in changes in the physical environment, not only are many of the events establishing such social commitments (like promises) entirely transient, but also their effects are dependent on a social agreement, which in turn is dependent on what our conspecifics believe. The transient nature of these social events is problematic both because, on the one hand, their committing force depends on their continuous influence through time and, on the other hand, by themselves they do not leave any physical traces of the events in question. If Susan promises Alan to meet him in front of the cinema at 8 p.m., she is obliged to be there, but this commitment survives (if at all) only in the mind of each party and perhaps of the witnesses of the interaction.

In principle, nothing but a reference to the specific occurrence establishing the commitment could be used to communicatively enforce the resultant obligations and entitlements. In fact, this is arguably one of the reasons for why humans have culturally developed so many “commitment devices”: ways of making such arrangements either physically traceable in the form of written contracts and other kinds of symbols, or making the commitment public so that it becomes impossible to deny one's obligation without damaging one's reputation with everyone who co-witnessed the event in question. Short of, and often in spite of, such commitment devices, however, nothing but one's memory of the interaction will be able to advocate whether and how obligations and commitments are distributed. If Susan does not turn up in time in front of the cinema, invoking Alan's memory of the interaction with Susan will allow him to confront her not just by citing the obligation that she failed to meet but also by justifying his belief in the existence of this obligation by referring to the event that generated it. The ability to explicitly refer back to specific past events is therefore essential for the argumentative negotiation of present obligations and entitlements.

3.4.2. Bookkeeping or remembering?

Social commitments have evolutionary significance because they make it possible for parties in an exchange to gain benefits that would be unattainable in the face of the risk of defection. Such commitments become important in the large spectrum of social relations in which the incentives of the involved parties are only partly aligned. As soon as incentives are entirely aligned or entirely misaligned, there is no room for such commitments to be effective because, in the former case, trust is not required, and in the latter case, trust is impossible. As Schelling (Reference Schelling1960) pointed out, such a situation of partly misaligned incentives characterizes the large majority of our social interactions. Thus, social commitments dramatically expand the range of possible ways of cooperation.

In principle, to make social commitments effective, all that is cognitively required is a mechanism that keeps track of the distribution of who owes what to whom (Brosnan & de Waal Reference Brosnan and de Waal2002; Schino & Aureli Reference Schino and Aureli2009; Reference Schino and Aureli2010). Such a “bookkeeping mechanism” does not need to consider the reasons for these commitments themselves. Bookkeeping allows one to keep track of and appropriately handle one's own and others' commitments. It also allows one to regulate one's trust toward others based on their willingness to reciprocate. Bookkeeping does not, however, allow one to argue for – and by arguing to effectively enforce, negotiate, or establish – one's entitlements. One can engage in various behavioral strategies to collect what one is owed or to retaliate against defection. However, being able to justify and thereby convince others about entitlements could avoid costly, and potentially escalating, physical conflict. Thus, episodic memory, by enabling reference to the past events that established specific entitlements, could serve the negotiation of cooperative interactions in humans.

3.4.3. Episodic memory content explained

These considerations then might provide an example for why humans should have developed a mechanism regulating communicative interaction about specific events in the past:

1. 1. Social commitments are often generated by singular events whose effects are solely dependent on the way these events can be referred back to by the parties involved or by their witnesses.

2. 2. The effects of social commitments always take place in the future, and their negotiation therefore will necessarily require representing them as having occurred in the past.