https://ndpr.nd.edu/reviews/depth-a-kantian-account-of-reason-2/
May 02, 2026
Depth: A Kantian Account of Reason
Melissa Zinkin, Depth: A Kantian Account of Reason, Oxford University Press, 2024, 296pp., $99.00 (hbk) ISBN 9780197786802.
Reviewed by Anastasia Berg, University of California, Irvine
2026.04.1
In his review of Susan Neiman’s The Unity of Reason: Rereading Kant (1997), an early entry in the “unity of reason in Kant” scholarly genre, Paul Guyer complained that the things Neiman describes as evidence for Kant’s single conception of reason, one account which can unify the apparently disparate realms of inquiry—theory and practice—and, correspondingly, being—nature and freedom—were “really similarities in our use of reason in the various areas of our inquiry and conduct.” (Guyer, 1997, 292). With this, Guyer set a basic standard for any subsequent attempt to answer the vexing question of the unity of practical and speculative reason in Kant. The question, to be sure, is Kant’s own. The “two separate systems” of philosophy, that of nature and that of freedom, are, Kant claims in the first Critique, “ultimately… a single philosophical system” (A840/B868), and he similarly insists in the Groundwork that “in the end there can be only one and the same reason,” unified “in a common principle (4:391, cf. also 5:91). But what that common principle might be Kant never stated clearly.[1]
Melissa Zinkin’s Depth: A Kantian Account of Reason is only one of the most recent attempts to secure the common principle or function that will lay bare the unity of the Kantian conception of the faculty of reason. It joins a diverse list of entries: reason’s regulative use in positing the practical postulates of God, soul and freedom (Pauline Kleingeld, Paul Guyer); practical reason’s ultimate object: the highest good (Jens Timmermann); the categorial imperative (Onora O’Neill, Alix Cohen); the standard of healthy human understanding (Melissa Merritt); a conception of reason as ‘comprehension’, understood a capacity for a specific kind of systematic understanding (Karl Schafer) and the principle of purposiveness (Sabina Vaccarino Bremner).
Every attempt to discover the hidden key to the unity of Kant’s theoretical and practical philosophies is ambitious, and Zinkin’s is no exception. Zinkin argues that what unifies reason is a principle, the principle of systematicity, which is the principle of “deep cognition and comprehension” (248). When reason judges in accordance with this principle, its judgments, theoretical and practical, have cognitive depth. (Zinkin’s argument thus, in its broad outlines, closely resembles Karl Schafer’s recent argument in Kant’s Reason: the Unity of Reason and the Limits of Comprehension in Kant, and indeed, it would have been helpful to hear more from Zinkin herself about how she views the differences between them.)
According to Zinkin’s Kant, human beings ought not only form correct judgments regarding the world, works of art and what to do but “become deep thinkers” (185), which means thinkers who strive not only to know what things are but why they are so: why horses are mammals, human beings rational and good actions good. Characterizing our mental lives as intrinsically aiming at depth is an attractive proposition, but I worry that the way Zinkin finds room for it in Kant risks depriving our so-called ordinary epistemic and moral lives of rationality itself.
The book is divided into two parts, dedicated to Kant’s theoretical and practical philosophy, respectively, with about half of the first part dedicated to Kant’s reflections on aesthetic judgment in the third Critique. In its pages, Zinkin illuminatingly weighs in on a number of open questions, e.g., Kant’s seven levels of cognition (Ch.1), the moral worth of Huckleberry Finn’s refusal to turn Jim in, contrary to his conception of his duty (Ch.5), and the transition from Section I to Section II in the Groundwork (Ch. 6). Limitations of space prevent me from going into these discussions’ interesting details, and I will have to limit myself to introducing and commenting on her central, broadest claims.
Zinkin is on surest footing in her treatment of Kant’s theoretical philosophy. In the first chapter, Zinkin introduces the claim that, for Kant, reason is the faculty of deep systematic judgment, which she identifies with Kant’s account of both “comprehension” in the Jäsche Logic (9:65) and reflective judgment in the third Critique. Zinkin rightly emphasizes that Kant’s concern with reason is not merely a negative one: to deny us knowledge by means of reason of anything that is beyond the bounds of experience and restrict the use of reason to a formal logical function as the store of the rules of inference. Rather, reason emerges as “a transcendental faculty that contains the conditions for the possibility of the cognition of objects”, where the cognition in question is not that of determinative judgments about what things are but “the insight into or comprehension of why something is what it is, that is, its organizing principle” (47).
The welcome redemption of reason comes, however, at a high cost. Zinkin asserts a sharp distinction between ordinary determinative judgments of experience and reflective judgments of reason: while determinative judgments are superficial, relying on “pre-given” concepts, deep reflective judgments are ones that employ concepts I “discover for myself”. This is the distinction between making the judgment x is p, say an animal is a mammal, because “it matches a description I have read in a book” (72), and making the same judgment “by discovering for myself that it has mammary glands.”
In the second judgment, “I, myself, have acquired the reason for making this judgment” (72). We already encounter a difficulty: even if there is a meaningful distinction to be drawn between the way in which I know most mammals, i.e., by learning about them from others, and the way I know those few where I happen to have had the occasion to observe the presence of their mammary glands “for myself”, is it right to think of the latter, DIY concepts, as inherently less superficial than the former, which I obtained from experts via written text?
Zinkin goes so far as to claim that ordinary determinative judgments are “mechanical and automatic, determined by habit or some already-given concept” (84). And correspondingly claims that when we judge determinatively, we judge “unreflectively and automatically, as when I am influenced by prejudice” (85). This seems to fly in the face of Kant’s profound concern with securing the rationality of our judgments, the sort of rationality that makes them fit to be the basis of inferences.
By contrast, for Zinkin, deep cognition amounts to cognitive “Freedom”: “the flexibility to apply what we have learned to new contexts—to think further and more deeply about something” (80-81fn14). The strong contrast between ordinary determinative judgments and deep ones threatens to preclude the expansion from one to the other since, and this I take to be of Kant’s most basic lessons, the gap between the mechanical and automatic and the rational is not one that can be easily bridged.
It is, of course, undeniable that our conceptual mastery can expand, as when a basic ability to identify, say, a dog, by a few basic characteristics of its appearance and behavior, develops into a broader and more systematic grasp not only of its form of life but also animal life in general, the division into species and genera, the history of human’s manipulation of dog’s breeds, etc. At the same time, we want an account of this development to illuminate the possibility of this development. This is precisely what characterizing basic determinative judgments in an empiricist fashion as “mechanical” and “automatic” obscures.
Moreover, while in learning what makes dogs dogs, I am deepening my understanding; arguably, the possibility of this expansion is already implicit in my basic determinative judgment. It is, in other words, constitutive of my basic, initial determinative judgments that they can be expanded by means of my gaining further information about what makes things the things they are.
And, finally, the process by which I come to know more things about dogs than I did initially is often no different than the one by which I came to learn to make my initial, simple judgment: by means of others. If I go deep sea diving, I may first consult a quick guide to identify a new life form I have never heard of, but surely in order to expand that knowledge, I am not really required to perform any experiments myself. I may continue to rely on others, my diving instructor, the authors of my guides, as I grow my understanding of this life form and connect it, systematically, to the rest of my knowledge of marine life. This is not the contrast between “mechanical, superficial judgment” (90) and “good, deep judgment”. It is rather the transition from fully rational and adequate empirical judgment employing a rudimentary grasp of concepts to rational empirical judgments employing a better—we might say deeper—grasp of concepts.
Finally, if ordinary exercises of empirical judgment were defective in the way that Zinkin suggests, it would not only be a mystery how I go from the superficial to the deep myself, but it would be unclear how any humans have ever come to possess “comprehension”, for the mechanical prejudicial judgments would hardly be fit to perform the justificatory role that they must in the growing of our complex, systematic empirical knowledge, i.e., what Zinkin’s “comprehension” is all about.
Moving to aesthetic judgements, we find Zinkin assimilating them without remainder to the judgments of comprehension. Beautiful objects, Zinkin claims, give us pleasure because they “deepen our cognition”. The unity and coherence of the beautiful object is, however, not sui generis; it is rather “precisely the systematic unity of reason”, the unity that “makes comprehension possible” (108). Zinkin speculatively proposes that beautiful objects occasion the following cognitive process: we encounter a particular X (e.g., a human being), for which the understanding has a rule, Xs are Fs (e.g., a human being is a rational animal). Then the imagination comes up, of its own accord, with an image of something else, we know not why or wherefrom, that could serve as a possible counter example to the rule (in her example, a cyborg). This prompts a reflection on the original rule: “The imagination playfully asks, ‘Could this thing be an instance of that object (the human)?” (111)
Recall that this process of contemplating a counter example to a rule is meant to be the basis of the judgment, this X is beautiful. Indeed, Zinkin goes so far as to suggest that “for Kant genius is the ability to come up with a good counterexample” (113 fn39). But nowhere does Zinkin take up the question of how the alleged capacity of an object to provoke the imagination to come up with “counter examples” relates to any familiar conception of beauty.
For the sake of argument, let us accept this picture of what gaining further understanding of a concept entails (it is far from clear that we should: Kant’s attempt to answer what human beings are does not proceed by imagining counter examples but takes the form of, among other things, three Critiques of our mental faculties). Surely, any specimen of X, beautiful or otherwise, would do as a basis for the initiation of this kind of furthering of understanding. Why think that the beautiful horse provokes our imagination to come up with fanciful counterexamples more that an average one would?
With this, we arrive at Kant’s practical philosophy. Zinkin’s basic account here parallels the one she offers of his theoretical enterprise. The familiar distinction between performing an action from a motivation that can be traced to our self-love and performing it in recognition of a necessity that can be traced to the very form of our rational capacities is replaced with an internal distinction within moral motivation: the distinction between “superficial” moral motivation and “deep” one. Zinkin claims that this distinction is analogous to the distinction between a case where I do something inscrutable because a friend, whom I trust, instructs me to (“throw this egg outside right away!”) and a case where I understand the end that my action will promote.
In the same way, Zinkin claims, an agent can grasp their duty in an ordinary moral judgment “tentatively and mechanically” (128) or, when contemplating the end of moral action, deeply and systematically. What the end of moral action is exactly varies: one ought to act in order to “cause my will to be good” (158); “give its actions moral worth” (159); “for the sake of humanity” (159); “for the sake of its own reason” (162); to “promote my own rationality” (162) or further “my own rational nature as an end in itself” (163); for “the end of promoting one’s own rational nature ” (241); and “for the sake of humanity as an end in itself” (232). This seems not only to give up on the idea of securing the sense in which, in acting from consciousness of the moral law, we do something that is good for its own sake, but to get things backwards. We do not treat human beings as ends to cause our wills to be good, we treat them as ends because this is our duty, because this is what respect for the moral law means, because it is the right thing to do.
Now, to be sure, it is reasonable to suppose, as Zinkin does, that one is likely to be more motivated, if only because far less perplexed, where one has a sense of why one is to do what one should. And one welcome consequence of this position that should be mentioned is the idea that to respect someone’s humanity is to respect their capacity for deep thought (192). This means that what I owe another human being extends far beyond not interfering with their power to choose as they happen to see fit but includes treating others as capable of reflective thought and deep comprehension. It follows that respecting other rational agents implies a duty to provide them with the opportunities necessary to develop their cognitive capacities. Moreover, this means that it is not enough to not treat others as means in a technical sense, by obtaining bare consent by whatever means necessary; treating others as ends in themselves means engaging their capacities of understanding and judgment fully.
But it is far from clear that this distinction between the superficial moral judgments and deep ones is helpful in understanding the distinction between common moral cognition and the sort of moral cognition made possible by philosophical inquiry. In effect, Zinkin assimilates ordinary moral judgments, those I have not “thought through” in the relevant way, to actions performed merely in accordance with the law, not from recognition of duty but from empirical motives. Accordingly, and startlingly, she goes so far as to claim that ordinary moral judgments’ prescriptions are “arbitrary”, “not authoritative and cannot obligate us” (158), and therefore, acting in accordance with such moral judgments has no moral worth (196). The implications are intolerable: anyone without philosophical grasp of morality is not obligated by the moral law.
For his part, however, Kant insists on the moral adequacy and worth of common human reason and its moral cognition. In the introduction to the Groundwork, he writes that while common human reason may “not think so abstractive in a universal form”, it nevertheless has the moral principle “always before its eyes and uses [it] as the norm for its appraisals” (4:404). He goes on to insist that “all moral concepts have their seat and origin completely a priori in reason, and indeed in the most common reason just as in reason that is speculative in the highest degree” (4:411).
Philosophy is not required to make moral action possible: “I do not, therefore, need any penetrating acuteness to see what I have to do in order that my volition be morally good” (4:403). We need moral philosophy not because without it, ordinary moral judgments remain without worth, but because though ordinary people are “capable of the idea of a practical pure reason”, their moral judgments “remain subjects to all sorts of corruption” (4:390). Innocence, Kant writes, is “splendid”, but “it cannot protect itself very well and is easily seduced” (4:405). By articulating the principle of pure practical reason vividly, practical philosophy helps us defend against these temptations. None of this is to suggest that it is prima facie unacceptable to advance a different, heterodox interpretation, but it is to say that such apparently straightforward statements must be addressed, and a case must be at least attempted to explain why we should be on better exegetical or philosophical ground in overlooking them.
Returning to Guyer’s standard: if Zinkin describes a single conception of reason, as a faculty of cognitive depth in theoretical, practical and aesthetic judgment, I remain skeptical that it is Kant’s. Even so, Zinkin articulates a valuable idea: our rationality finds expression in our ambition not only to get things right but to gain further and further insight, by means of expanding and systemizing our knowledge, whether of the world or of how we should conduct ourselves in it. I remain hopeful that it is possible to find it in Kant, and articulate it philosophically, without dismissing so much of our ordinary, pre-philosophical mental lives.
REFERENCES
Guyer, The Philosophical Review, Vol. 106, No. 2, April 1997.
[1] Kant’s works are cited according to volume and page number in Kants Gesammelte Schriften, ed. Deutsche (formerly Königlich-Preussische) Akademie der Wissenschaften (Berlin: G. Reimer, 1900–19; De Gruyter, 1920–). The Critique of Pure Reason is cited according to the page numbers in the first (‘A’) and/or second (‘B’) editions. Whenever available, English translations are taken from Cambridge Edition of the Works of Immanuel Kant, abbreviated as ‘CE.’
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