Suddendorf & Corballis (S&C) propose that the capacity to mentally transport oneself into future situations imagined in concreto is a uniquely human cognitive adaptation that has not only played a decisive role in our evolutionary past but may also account for a large part of our current dominance on Earth. The case they make for this is, however, encumbered with difficulties, of which I will comment on a few largely conceptual matters.
Foresight – the ability to anticipate future needs and to act accordingly – is the key concept and source of utility in the authors' account. As they are well aware, foresight can be served by either direct semantic prospection or more round about mental time travel directed to the future. In fact, every single example illustrating foresight by means of mental time travel provided in the target article can be implemented by direct semantic prospection instead. But that means that those examples illustrate only the utility of foresight – which no one doubts – but not the specific utility of mental time travel for that purpose, as intended and implied by the authors. Thus, rehearsal for questions that may be posed in a forthcoming job interview (sect. 2.1) is readily accomplished through semantic prospection (“I wonder what questions I'll get? Maybe this one...” etc.). What is more, S&C provide no concrete evidence that mental time travel ever yields information whose efficacy for success in planning for the future exceeds that provided by semantic prospection. Such information may in fact be unavailable in principle, for reasons connected with the nature of time and its relation to memory and imagination.
Occasional qualifications made in passing notwithstanding, the authors' entire argument is built upon a perfect symmetry between past and future, as strikingly illustrated in Figure 1 of the target article. Yet time itself, along with the causality of the macroscopic world, is profoundly and fundamentally asymmetric with respect to past and future. The past has actually happened, which means that it once was the present, and thus subject to memory storage by suitably equipped organisms (which is how it became “the past”). That means that in principle, at least, the possibility of veridical memory exists. There is no corresponding possibility with regard to the future, because the future has by definition not happened, being a mixture of coexisting latent possibilities as yet unresolved. Which of these is the “true future” cannot be known until it has “travelled to us,” and become the present. Similarly for causality: In the macroscopic world the effect follows the cause in time, but never the reverse. That is how the present (cause) becomes a memory (effect) by the next present along future-directed causal pathways.
It is the existence of a more or less veridical memory for the past which, on occasion, lends utility to revisiting that past in the imagination through mental time travel instead of relying on the distillate of that past provided by semantic memory. Let us say new circumstances have rendered a detail that did not seem important at the time relevant to our present concerns. Occasionally, we are in fact able to recover such detail by going back and “reliving,” as it were, the situation in question, though that utility is in all likelihood a rather marginal one. The veridical memory is the “destination” towards which we steer in retrospective mental time travel. There is no such destination for prospective mental time travel, because unlike the past, the future has not happened and all we can know is that all possible futures, except one, will in fact not materialize, but not which one.
That is, the great flexibility of future time travel which the authors tirelessly extol as its great advantage is to no avail as far as foresight is concerned, because the utility of anticipating the future for prudential purposes does not hinge on the number of imagined alternatives, but on being correct, and such prediction is possible only to the extent that the future is in fact foreseeable, which means being “like the present and the past” (see next paragraph). Moreover, nothing is less certain in that regard than the fine grain (“particularities”) of imagined futures, the one additional advantage ascribed by S&C to actual mental time travel compared to semantic prospection. These points can be illustrated by the importance of correctly anticipating which questions will in fact be asked in a forthcoming job interview. Preparation for the wrong questions is wasted effort, and may even act as an impediment during the interview. Needless to say, mental time travel possesses no privileged power to pick the right questions.
What are we to make, then, of the striking parallels the authors array between past and future in human performance? In light of what has gone before, the answer is readily available. The only aspects of the future that are in fact predictable are those respects in which it continues to be like the past (at all time scales and in any number of attributes and statistical characteristics). When, therefore, we construe possible futures, they share vast domains of content with the present and its past states of variation vouchsafed by memory, whether semantic or episodic. In doing so, we are in fact in large measure projecting the past into the future, abstractly or concretely, and not “travelling” into it. The parallels listed by S&C follow as a matter of course.
To summarize: What the authors call mental time travel into the future is prospective fantasy and the use of imagery in scenario-building (for the latter in relation to the frontal lobes, see Nauta Reference Nauta1971). These have their uses, in various creative endeavors, say, endeavors which certainly may affect and change the future. That, however, is a matter of the extent to which those endeavors recruit workable causal channels for their implementation, and not of any special efficacy for actually anticipating the future on the part of the fantasies that inspire them, as the record of failed prospective fantasy supplied by human history reminds us.
