Products of scientific discovery can be objects, properties, and phenomena on the one hand, as well as laws, hypotheses, and theories on the other. Most philosophical discussions of scientific discoveries have focused on the generation of new theories that fit or explain given data sets or allow for the derivation of testable predictions. Over the past century, the so-called context distinction (associated with Hans Reichenbach, Experience and Prediction: An Analysis of the Foundations and the Structure of Knowledge [Chicago: University of Chicago Press, 1938])—the distinction between the “context of discovery” and the “context of justification”—has dominated philosophical discussions of theoretical discoveries. Most commonly this is interpreted as a distinction between the process of conceiving a theory and the subsequent validation of that theory, that is, the determination of the theory’s epistemic support. Although this distinction, at least as it is commonly interpreted, seems to imply that discovery per se is restricted to the first, relatively short process—that of conceiving—there have been scholars at least since William Whewell (The Philosophy of the Inductive Sciences, vol. 2 [London: Routledge/Thoemmes, 1840/1996]) who have considered discovery to be an extended process equally consisting in conceiving of a new idea, developing and articulating it, and subsequently validating it.

What about the discovery of objects and phenomena in nature? What constitutes discovering a protozoan, or a planet, or radioactivity? Here, the idea that discovery—be it with the aid of the senses or instruments, serendipitous, by a stroke of genius, or by continued efforts—is simply the singular act of spotting something new in nature, often by an individual scientist, has for long engaged popular imagination. Common textbook claims such as “Galileo peered through his telescope and discovered the moons of Jupiter in January 1610” attest to this. In this fantastic and comprehensive work on discovery and classification in astronomy, Stephen Dick shows us, via a wide array of case studies spanning the realms of planets, stars, galaxies, and more, that such a simple view of discovery that takes it to simply consist in finding or spotting by observation cannot be further from the truth. According to him, discovery goes well beyond observation or detection, including interpretation and understanding. Moreover, sometimes the detection stage is altogether replaced by indirect inference of an object’s existence. A central thesis of the book is that discovery of astronomical objects and phenomena—like the discovery of theories as above—is an extended process. Particularly in astronomy, classification of objects and phenomena is closely tied up with discovery and is often itself a complex and extended process. But in making this point about discovery and classification being extended processes, Dick draws our attention to the essential and critical role of social factors in driving and shaping discoveries. Discovery is an extended process not only in that it is achieved in multiple stages (detection, interpretation, understanding) but also in that it is extended over time (sometimes over several years) and, importantly, shared across persons.

Dick discusses several case studies exemplifying his tripartite structure of discovery, but one particularly illuminating case is that of the discovery of the rings of Saturn. Dick tells us that while Galileo detected them in 1610, he had no idea what they were. To him, they were nothing more than strange, handle-like appendages. Subsequently, it was Christiaan Huygens who in 1655 interpreted what had been detected as rings, and further, it was James Clerk Maxwell who in the twentieth century provided theoretical understanding of the rings by demonstrating how this formation could be possible based on dynamical considerations. So who discovered Saturn’s rings? Dick’s answer is that it was all three of them—Galileo, Huygens, and Maxwell; discovery is most usually collective as opposed to individual. Further, the discovery of rings of other planets (Uranus, Jupiter, and Neptune) in the late twentieth century firmly established the existence of rings as a new class of objects.

While each of Dick’s three components of discovery—observation, interpretation of findings, and understanding in science—has been subjected to intense scrutiny and analysis within philosophy of science, Dick shows us that a complete understanding of the components and overall structure of discovery (unsurprisingly) calls for a holistic approach to the subject, including scientific, philosophical, historical, and sociological perspectives. Following the pioneering works of Michael Polanyi, Ludwik Fleck, Robert Merton, and Thomas Kuhn, among others, Dick reminds us that contrary to long-held traditional views, science doesn’t consist of disembodied theories and facts, but comes from scientists who are real people working in specific historical, sociological, and cultural contexts. For instance, as Dick tells us, Percival Lowell’s “obsessive personality and the abundant funding” (193) played a big role in the initial finding of Pluto. Again, Pluto’s “demotion” to the status of a dwarf planet in 2006 was due to a classification that was based on the physical properties of the objects in question (like mass and hydrostatic equilibrium), but the choice of classification criteria was socially negotiated and was decided on the basis of a vote by members of the International Astronomical Union. While emphasizing the social elements of discoveries, though, Dick equally emphasizes that his is far from a radical postmodernist, social constructivist position. He categorically denies that scientific discoveries are “socially constructed to such an extent that those discoveries have no basis in reality” (191). For Dick, while the process of discovery is socially constructed, what is discovered is not.

While Dick’s point that discoveries are multistaged and extended over time and across persons is importantly true, his demarcation of the process into three distinct stages seems a bit contrived. That discovery goes beyond just detection is no doubt convincing, but the need for two more distinct stages—interpretation and understanding—is not, for the difference between the two stages is not clear. What exactly demarcates interpretation from understanding? For instance, in the case of asteroids, Dick tells us that Piazzi detected the first one in January 1801 without knowing what it was, and that it was over a year before William Herschell, on finding more such objects, declared the existence of asteroids as a new class and put Piazzi’s object in the class. (Further, acceptance of this new class by astronomers took finding many more similar objects, which took about 50 years.) But Dick does not make it clear which stage in this story counts as interpretation and which as understanding. There don’t seem to be precise accounts of interpretation and understanding in Dick’s work, and hence I think it might be better to clump them together and then make finer distinctions as needed on a case-by-case basis. As I see it, interpretation and understanding, if they differ, differ in degree, not in kind. To take another example, then, seeing the “appendages” of Saturn as rings and then theoretically backing the physical possibility of rings can just be taken as two levels of understanding, with the latter providing deeper understanding than the former. The interpretation-understanding distinction does not seem warranted.

The Saturn and asteroid stories above (among several others in the book) nicely serve to highlight one of Dick’s central points—that discovery is closely tied up with classification. As Dick says, “A new object will have barely been discovered before the human mind tries to determine where it ‘fits’ in the order of things already known” (233). (And I presume he would add that when an object does not fit in the order of things already known, we are forced to accommodate it in a new class before claiming to have “discovered” it.) In the Saturn case, for instance, according to Dick, while Galileo detected something around Saturn, it is not until it was identified as rings that Saturn’s rings were discovered per se. Discovery for Dick, then, is discovery as something—rings were not discovered until they were classified as rings, and as teroids were not discovered until they were classified as asteroids. But although classification plays a big role in discovery, classification doesn’t always end with discovery—for Dick, a discovery is considered complete when we have a basic enough understanding of the object or phenomenon in question. But often classification systems can continue to get more and more sophisticated and more and more complete and can extend well beyond the discovery process. In the case of Pluto, given that it was stripped of planetary status nearly 75 years after its initial discovery and put into the class of dwarf planets, we can probably say that Pluto was rediscovered in 2006.

Although Dick takes classification to be unique to the discovery of “localizable natural objects” (233), discovery of theories and laws has also been associated with classification—for instance, Pierre Duhem (The Aim and Structure of Physical Theory, trans. from 2nd ed. by P. W. Wiener [Princeton, NJ: Princeton University Press, 1914/1954]) took the aim of physical theory to be to neatly classify experimental laws (and laws to classify phenomena). Further, the aim in astronomy is always a realist one so to speak. Quoting an astronomer, Dick says, “The goal of any classification system, either in biology or astronomy, is to reveal underlying physical properties” (276). This is again reminiscent of Duhem’s view that the ideal end for physical theory is to provide a classification of laws that perfectly mirrors a natural classification—the classification of underlying realities. In fact, classification in general seems to line up with an important concept in the philosophy of scientific discovery—Whewell’s “colligation.” According to Whewell, colligation is a key element of (theoretical) discovery that consists in bringing together a set of facts under a general conception—much like bringing together multiple similar objects under a class. Interestingly, Whewell’s colligation is also an extended, iterative process—it involves spelling out facts via empirical means and coming up with ideas that colligate them. (In another interesting parallel with Dick, Whewell had his own tripartite structure of discovery that consisted in a “happy thought” or conception of a new idea, colligation, and verification of the colligation.)

Finally, following Herschell’s celebrated comparison of the heavens to a “luxuriant garden” consisting of a plethora of variety of objects (similar to biological species) like planets, asteroids, stars, nebulae, globular clusters, and so on, Dick provides several insights throughout the book into similarities and differences between biology and astronomy with respect to many aspects of classes and classification systems, such as criteria for membership, common ancestry, and familial affinities. Inspired by biological kingdoms, Dick’s work culminates in a grand “Three Kingdom System” based on the physical natures of objects and comprising the kingdoms of planets, stars, and galaxies. Like in biology, this system is hierarchical, extending from kingdom to family to class (and with possibilities for extension into further categories such as type and subtype). This very comprehensive classification system is in my view one of the most unique and significant contributions of the book.

Overall, what Dick has given us is an excellent and comprehensive treatise on the science, history, philosophy, and sociology of discovery and classification in astronomy. There is much to take from Dick’s work, both from the elaborate scientific and historical details of the case studies and from the rich analyses of them from a synergetic science studies perspective.