COREY DYCK | Kant and Rational Psychology | Oxford University Press 2014


By Colin Marshall

There are just too many words in the history of philosophy for anyone to read them all. There may be too many words for anyone to read even in seventeenth and eighteenth century European philosophy alone, though I can think of a few people who might come close. Either way, there are certainly too many words in the period for anyone to read them all well, and to think carefully through the connections between the different authors. For that reason, there is a standing temptation towards lazy dismissiveness when doing the history of philosophy. Deep down, we want to know that certain authors are not worth our time, and to know that without having to carefully read their works.

Christian Wolff, who wrote an especially large number of words, seems to have brought out this temptation in many historians of eighteenth century philosophy, despite his fame and success during his life. One of the many valuable contributions in Corey Dyck’s Kant and Rational Psychology is an extended argument that Wolff and his immediate successors are indeed worth our time, especially if we want to understand one of the best-received chapters from Kant’s First Critique: his attack on rational psychology in the Paralogisms of Pure Reason. Many of Kant’s readers have thought that it is enough to understand Kant’s target in the Paralogisms to look at the works of Descartes and Leibniz, and have taken Wolff to be a second-rate rationalist who added nothing significant to the tradition except some jargon. Against this, Dyck argues:

In ignoring Wolff and the philosophers influenced by him […] we ignore a tradition that developed a radically new methodology in investigating the soul, one that […] serves to distinguish it in a number of ways from that narrowly rationalistic approach to the soul attributed to Descartes and Leibniz. (p. 2)

It would be a mistake […] to think that all that a consideration of the German tradition of rational psychology in the 18th century can yield is additional detail regarding what are, at bottom, Cartesian and Leibnizian positions on the soul. This is because the rational psychology developed by Wolff departs in a number of crucial respects from that which can be extrapolated from the texts of his classical predecessors. (p. 9)

Dyck is not the first Kant scholar to devote serious attention to Wolff, but he is certainly in the minority.

Dyck’s main topic in this book is Kant, not Wolff, but my focus will be on his argument about the distinctiveness of Wolff’s philosophy of the soul, leaving his interpretive claims about Kant for Scott Edgar and Andrew Brook. In effect, I am sorry to say, I am going to be defending the lazy temptation. More specifically, I am going to argue that the features of Wolff that Dyck claims are distinctive can be found in the least-ignored early modern rationalist: Descartes.[1] One reason for doing this is to prompt Dyck to go a bit further in his argument, for while Dyck notes at the end of the book that Leibniz might be closer to Wolff than his earlier discussions suggested, he seems to think the contrast is clearest with Descartes (see pp. 227, 232). Another reason for my topic is to resist a caricature of Descartes that I think many philosophers (including Kant) are prone to. But my main reason is that Descartes is surely one of Kant’s primary targets in the Paralogisms, so we stand little chance of evaluating the aims and success of Kant’s claims there without an accurate understanding of Descartes. Remember that Kant thinks that there is a deep continuity in metaphysics, and that the temptation towards specific dogmatic metaphysical claims comes from human reason itself. To determine whether Kant is right, we should look carefully at how much continuity there is among Kant’s metaphysically-inclined predecessors. I suspect that, if I am right, the similarity between Descartes and Wolff will be more helpful than harmful to Dyck’s larger project (along the lines suggested in the final chapter of his book).

I begin by discussing two general features that Dyck claims distinguish Wolff’s philosophy from those of his predecessors: Wolff’s use of experiences and hypotheses. Both features, I will argue, can be found in central parts of Descartes’ philosophical project. I then turn to the specific branch of Wolff’s and Descartes’ philosophy concerning the nature of the soul. Dyck argues that here in particular Wolff gives experience a deeper role than his rationalist predecessors. I will argue that Descartes’ use of experience seems to be just as deep on this front, even if some details about those experiences differ. I conclude by making a cautious point of comparison between Descartes and Kant.

1. Descartes and Wolff on general philosophical methodology

Dyck claims that Wolff departs from his rationalist predecessors on a quite broad methodological level, both in his wide-ranging use of philosophical hypotheses (that is, unproven propositions) and in his use of certain kinds of experience to provide the principles and confirmations for even the most abstract areas of metaphysics. There is, to be sure, a way of reading some of Descartes’ work (such as the Principles of Philosophy) which suggests that Descartes held that philosophy begins with indubitable principles and proceeds through pure deduction. That kind of project would indeed have no use for mere hypotheses and experiences. We do not have to dig very deep into Descartes’ writings, however, to see that that hyper-rationalist reading of Descartes is a caricature. I will start with the role of hypotheses.

1.1 The use of hypotheses

Dyck writes:

Wolff’s innovation lies in the fact that he extends [philosophical hypotheses’] use into all the domains of metaphysics. […]. By definition, a philosophical hypothesis is a merely probably proposition and as such it is misused when it is employed as a principle in a demonstration of some further claim. (p. 26)

The question, then, is whether Descartes employs merely probable propositions in all areas of metaphysics. Now, there is no question that Descartes’ goal is to achieve certainty in metaphysics, and that he thinks this goal is at least partly attainable. That does not imply, though, that he cannot use hypotheses en route to achieving that certainty. This turns out to be what Descartes in fact does. I will give two examples.

The first example appears at the beginning of Descartes’ two major works on metaphysics: the Meditations and the Principles. The hypothesis in question is that whatever is even merely doubtful is false.[2] This is a hypothesis for him because Descartes does not believe it is certain that whatever is doubtful should be considered false, rather, this is just a temporary tool for discovering something firm and lasting for the sciences (AT 7:17 [CSM II:12]). The hypothesis could not occur at a deeper level of Descartes’ project, since he uses it in order to find his first point of certainty. That is why both the Meditations and the Principles emphasize that this hypothesis should be employed only once in one’s life.

The second example of Descartes’ use of hypotheses may be less familiar. In Descartes’ early treatises, The World and Treatise on Man (originally written as parts of a single work), he asks us to set aside the nature of the actual world to “allow your thought to wander beyond this world to view another world—a wholly new one which I shall bring into being before your mind in imaginary spaces” (AT 11:31 [CSM I:90]). Part of this world are fictional men, consisting of minds and bodies (AT 11:119 [CSM I:99]). Presumably because of worries of censorship, Descartes’ strategy is to show how his non-Aristotelian metaphysics and physics could account for a world just like the one we experience, without immediately taking a stand on the origin and nature of our world. Descartes describes this in the Discourse as follows:

I decided to leave our world wholly for [“the learned”] to argue about, and to speak solely of what would happen in a new world. I therefore supposed that God now created, somewhere in imaginary spaces, enough matter to compose such a world. […] I expressly supposed that this matter lacked all those forms or qualities about which they dispute in the Schools. (AT 6:42–3 [CSM I:132])

As with the first example, these hypotheses occur at a foundational place in Descartes’ system. That system aims at certainty, but does not claim to start with it. To achieve certainty after using these hypotheses, Descartes appeals to certain kinds of experiences.[3] That brings us to the second point of methodological comparison.

1.2 The use of experience

Dyck writes that, for Wolff, “reason and experience are envisioned as forming a complementary whole, where experience provides an indispensable basis for properly philosophical cognition and even serves to confirm the latter’s results” (p. 21). Wolff does this, Dyck claims, “in conscious opposition to his rationalist predecessors […] fault[ing] Descartes, for instance, for attempting to posit universal metaphysical principles ‘from which one will deduce through the mere understanding everything that is possible in nature’” (pp. 26–7).

The previous section has given us one reason to reject this picture of Descartes. Before giving additional reasons, I should note an ambiguity in Dyck’s account. Often, Dyck writes as though Wolff held that experience must be at the basis of every philosophical principle. Other times, though, it sounds as though Wolff held a much weaker claim, according to which all that is strictly required is that experience be consistent with what is discovered through purely rational means. For instance, Dyck attributes to Wolff the claim that “in doing rational psychology […] what is discovered through inference must be confirmed or, failing any relevant experience, at least not contradicted by what we can observe of the soul” (p. 6, my emphasis). No major early modern rationalist would allow that experience ever contradicts what we discover in rational investigations. I will assume, then, that Dyck finds the stronger claim in Wolff, namely, that all philosophical principles must be founded on experience.

Now, Descartes clearly does not think that every philosophical principle is founded, even in part, on raw sensory experiences. As Dyck makes clear, though, the relevant notion of experience in Wolff is not a matter of raw sensory experiences, but rather a technical notion of an ‘infallible’ or ‘clear experience’ which “has its origin in attention to our perceptions, but […] is [also] the object of a rigorous investigation using a variety of methods by means of which we can be assured that that which we experience is in fact the case” and which involves “essential contributions from both the senses and the higher faculties” (p. 22). This makes the contrast with Descartes less clear. A crucial question is what the “perceptions” are which clear experience involves. If these are raw sensory perceptions, then we may still have a contrast with Descartes (and Leibniz, for that matter).

None of the material Dyck quotes from Wolff indicates that clear experiences must be sensory, however. Wolff, according to Dyck, defines perception as the representation of an object (p. 106), but even that doesn’t require sensation. Perhaps the most telling case comes in Dyck’s discussion of Wolff’s account of the basis of the principle of non-contradiction. Wolff, Dyck claims, bases the principle of non-contradiction on our experience that the mind cannot at the same time judge something to be and not to be (p. 22). It is hard to see how that kind of experience would require raw sensations, so the relevant perceptions must be of some broader sort that includes the self-perception of our own attempts at judging. If the perceptions of certain experience can include such self-perception, though, then Descartes and Wolff would be on the same page.[4]

Before looking at the role of experience in Descartes’ account of the soul, however, we should consider the general role that experience plays in Descartes’ philosophical project. Two points are relevant: Descartes’ distinction between analysis and synthesis, and his views about the limitations of what can be derived from his principles.

First, in the Second Replies to the Meditations, Descartes responds to a request (probably by Mersenne) to present his views in a geometrical fashion. Descartes begins by distinguishing what he calls “analysis” and “synthesis”. The former “shows the true way by means of which the thing in question was discovered methodically” (AT 7:155 [CSM II:110]), is “the best and truest method of instruction, and it was this method alone which I employed in my Meditations” (AT 7:156–7). Synthesis, by contrast, “demonstrates the conclusion clearly and employs a long series of definitions, postulates, axioms, [etc.]”, but “is not as satisfying as the method of analysis… since it does not show how the thing in question was discovered” (AT 7:156 [CSM II:111, my emphasis]).[5] Syntheses works well for geometry, Descartes grants, but that is because “the primitive notions which are presupposed for the demonstration of geometrical truths are readily accepted by anyone. […]. In metaphysics by contrast there is nothing which causes so much effort as making our perception of the primary notions clear and distinct” (AT 7:156–7 [CSM II:111]). The model of rationalism that Wolff, according to Dyck, describes to Descartes would be the synthetic method. Descartes does think that approach has its place, but he denies that it is the way we discover metaphysical truths. This distinction goes at least some ways towards helping make sense of the apparent inconsistency in Descartes that Dyck discusses in Chapter 6 (see pp. 175–6). Cartesian analysis, as we will see below, does involve certain kinds of experiences.

Second, even in the ideal case where we have the first principles established, Descartes does not think that the first principles will entail everything we want to know. Rather, as Descartes writes in the Discourse:

[T]he power of nature is so ample and so vast, and these principles [I have discovered] so simple and so general, that I notice hardly any particular effect of which I do not know at once that it can be deduced from the principles in many different ways, and my greatest difficulty is usually to discover in which of these ways it depends on them. I know no other means to discover this than by seeking further observations (AT 9:64–5 [CSM I:144])

Observation and experience, then, seems to have an essential role in systemic philosophy for Descartes, even after the discovery of first principles. Note that this is more than just requiring that the principles be consistent with experience, and more than requiring they be confirmed by experience. Rather, experience is needed to discover how almost “any particular effect” is related to those principles.

2. Descartes on Wolff on experience and discovering the nature of the soul

The above general points about Descartes’ method will be useful in considering the more specific question of whether Wolff offers something radically new (or, at least, radically non-Cartesian) in his approach to the investigation of the soul. Dyck claims that Wolff’s “most important innovation” (p. 19) was to emphasize the interdependence of the empirical and rational sides of the science of the soul, where the empirical side is defined in terms of the use of experience. As we have seen, though, the relevant sort of experience includes the observation that the mind cannot both judge something to be and not to be. Descartes may not use the label ‘experience’ for that kind of self-awareness, but that is just a terminological difference. Self-perception plays a crucial role in Descartes’ analytic method.

There is one topic on which Dyck seems to grant as much, namely, how we are aware of our own existence. He writes that Descartes’ influence upon Wolff “is most evident in his discussions relating to empirical psychology, particularly in Wolff’s account of how we can be certain that we exist” (p. 4). Presumably, this concerns the “indubitable experience” Wolff describes of finding that no one can doubt that they exist “since to do so is already to be conscious of that which I am doubting” (p. 29, see also p. 178). This case reinforces how far Wolffian ‘experience’ can stray from raw sensation. Note, though, that Descartes never denies that sensation is present throughout this line of thought. Contrary to how he is sometimes read, Descartes does not claim in the Meditations that embodied beings like us can engage in intellectual acts without something sensory occurring, and even of a sensation of something as distinct from us (see his discussion of imagination and understanding at the beginning of Meditation 6).[6]

Though Dyck recognizes some similarity between Wolff and Descartes on this point, he does not seem to recognize how far it goes in undermining his contrast between Descartes and Wolff. For the awareness of one’s own existence is the Archimedean point of Meditation 2, and so Descartes’ very first principle. If experience is at the basis of this principle, then Descartes’ entire metaphysical system, on the analytic method (which, recall, is prior to the synthetic method), is likewise based on experience, and there is no deep contrast between him and Wolff.

Experience, in this broad sense, appears at other crucial places in Descartes’ analytic method. I will briefly discuss three that illustrate his similarity to Wolff: Descartes’ account of our awareness of our different mental faculties, his account of our awareness of the soul’s simplicity, and his account of our understanding of the mind-body union.

2.1 Faculties

In Meditation 4, Descartes is explicit that he comes to know the nature of two of his faculties on the basis of some sort of self-perception:

[W]hen I look more closely at myself and inquire into the nature of my errors […] I notice that they depend on two concurrent causes, namely on the faculty of knowledge which is in me, and on the choice or freedom of the will. […]. If […] I consider the faculty of understanding, I immediately recognize that in my case it is extremely slight and very finite. […]. Similarly, if I examine the faculties of memory or imagination, or any others, I discover that in my case each one of these faculties is weak and limited (AT 7:56–7 [CSM II:39–40])

Descartes does not deduce the existence of his faculties from any pure principles, nor does he even consider that possibility. The self-observation he describes here would seem to be as much a matter of experience as Wolff’s discovery that we cannot both judge something to be and not to be. Something similar happens later, in Meditation 6, where Descartes argues for the distinction between imagination and understanding (AT 7:72–3 [CSM II:50–1]). These distinctions are crucial to Descartes’ overall account of the mind.

2.2 Simplicity

Descartes’ second argument for the mind-body distinction appears late in Meditation 6. The most relevant part of the argument is his claim that “when I consider the mind, or myself in so far as I am a thinking thing, I am unable to distinguish any parts within myself” (AT 7:86 [CSM II:59]). Descartes has to note that the distinctions he has made in faculties do not undermine the simplicity of the mind. What is most important again here, though, is Descartes’ explicit use of self-directed observation. He does not claim to deduce the simplicity of the mind from any principles. If anything, Wolff’s approach to discovering the simplicity of the soul, on Dyck’s description, seems to be less directly dependent on experience, for Wolff derives the simplicity of the soul from other features of the mind:

[G]iven that we are conscious and the consciousness requires the faculties of reflection and memory […] and given that a composite cannot possess these faculties […] it follows that the soul is not composite but is instead a simple thing […] a substance […] and a power or force. (p. 32)

For Wolff, it is not the simplicity of the soul that is demonstrated directly but rather the soul’s immateriality, from which its simplicity is taken to follow (p. 106)

2.3 Relation to body

Finally, we find a surprisingly strong appeal to sensory experience in Descartes’ correspondence with Princess Elisabeth. Elisabeth objects to Descartes that she cannot understand how the mind and body, as substances with distinct natures, can causally interact, and suggests that this inclines her to think that the mind has physical properties. Descartes replies that the relation between mind and body cannot be understood through our ideas of the mind and body alone, but instead requires a distinct primary notion of their union. For our purposes, what it most important is how Descartes thinks we achieve this grasp of the union:

The soul is conceived only by the pure intellect; body […] can likewise be known by the intellect alone, but much better by the intellect aided by the imagination; and finally what belongs to the union of the soul and body is known only obscurely by the intellect alone or even by the intellect aided by the imagination, but it is known very clearly by the senses […]. Metaphysical thoughts, which exercise the pure intellect, help to familiarize us with the notion of the soul; and the study of mathematics […] accustoms us to form very distinct notions of body. But it is the ordinary course of life and conversation, and abstention from meditation and from the study of the things which exercise the imagination, that teaches us how to conceive the union of the soul and the body. (AT 3:691–2 [CSM III:227])

Descartes’ discussion here is an elaboration of his claims in Meditation 6 that experiences like hunger and pain show that we are not merely present in our bodies the way a sailor is present in a ship (AT 7:81 [CSM II:56]). To properly conceive the relation between the mind and body, then, requires experience of the most raw, most sensory type. If we set aside such experience and employ the intellect alone, Descartes thinks, we will be misled in understanding the relation between mind and body, which can tempt us (as it did Elisabeth) to question the immateriality of the soul. What Descartes recommends here is nothing like a deduction from abstract intellectual principles. I would be curious to hear which part of Wolff’s philosophy Dyck thinks comes closest to this strong appeal to non-intellectual experience.

3. Descartes and Kant on the unquestioned reference of “I”

To conclude, I want to set Wolff aside and briefly discuss one point of comparison between Descartes and Kant. Dyck argues that, for Kant, the representation ‘I’ is based in the representation ‘I think’ (see 72–9). There is a lot to say about this intriguing suggestion, which echoes various earlier anti-metaphysical readings of Kant. What I want to emphasize, though, is the fact that Kant uses ‘I’ and related terms (‘mind’, ‘soul,’ and occasionally ‘self’), in an apparently unapologetic and referential way throughout the Critique, long before he gets to the discussion of the ideas of reason in the Dialectic. This stands in contrast to other rational ideas, such as those of the world-whole and God, which Kant makes no significant use of in the earlier parts of the Critique. The most natural way to understand all this is to take Kant to hold that the concept ‘I’ has a perfectly straightforward, referential use. This might make us worry about the consistency of the rest of the Critique with the A edition of the Paralogisms.[7]

The comparison with Descartes is helpful here. In Meditation 2, Descartes reaches the conclusion that he exists. This substantive conclusion, though, comes after a discussion in which ‘I’ was consistently used in an apparently referential sense. Even in the depths of Meditation 1, where he claims to have discovered universal doubt, Descartes continues to use ‘I’ and assume the existence of some sort of subject. The doubt-sustaining image he provides at the end of that meditation is of the evil genius who is bent on deceiving him. As some of Descartes’ readers (more memorably, Lichtenberg) have noted, this might make us worry that Descartes’ ‘discovery’ of his indubitable existence in Meditation 2 is not a discovery at all, but instead the restatement of a standing assumption that was used to frame his doubts.

The parallel between Descartes and Kant, therefore, is this: both of their central discussions of the nature of the ‘I’, soul, or self are made with apparent unapologetic references to this entity. Both Descartes and Kant raise challenges to traditional metaphysics, though, that are easily read in a way that suggests they should not have made such unapologetic references. If these interpretive issues are indeed parallel, then understanding Descartes may shed light on some of the most obscure questions concerning the consistency of Kant’s doctrine of the soul.


Just to be clear, I am not saying that Dyck should have written a book about Descartes and Kant instead of one about Wolff (and his followers) and Kant. Instead, I have been challenging his claim that Wolff’s approach to understanding the soul shows a fundamental break with Descartes’. As you might have guessed, I am hoping that this means that I can continue to read Kant without putting as much time into reading Wolff as Dyck has, while still being able to tackle Dyck’s interpretive claims about Kant. Less selfishly, and more realistically, though, I hope that my comments here will provide an occasion for Dyck to clarify the nature of Wolff’s innovations and so deepen his challenge to the many Kant scholars who have become used to skipping from Leibniz and Hume to Kant.

An earlier draft of this essay was read at an Author Meets Critics symposium at the Canadian Philosophical Association, on June 3rd, 2015.


[1] As a crude measure of who is ignored: a May 2015 Google search for ‘Descartes’ gets about 20.8 million results. ‘Leibniz’ gets 11.6 million, ‘Spinoza’ gets 10.6 million. ‘Wolff’ gets 49.6 million, but there are a lot of Wolffs out there. ‘Christian Wolff’ gets 427,000, but many of those are for a contemporary experimental composer. Kant, for the record, gets 94.2 million results (more than even ‘Plato’), the vast majority of which are about the philosopher.

[2] In the Principles: “What is doubtful should even be considered false” (AT 8A:5 [CSM I:193]), see also Part 4 of the Discourse (AT 6:31 [CSM I:126])

[3] Another useful comparison here is with Spinoza. Book II of the Ethics contains several postulates, which Spinoza takes to be less than certain rational principles (see the scholium to 2p17), but which play an important role in explaining the nature of the human mind.

[4] Similarly with the sense in which Crusius, according to Dyck, relies on experience (p. 52). Of course, Descartes’ use of ‘perceive’ (percipio) is very broad, since it includes clear and distinct perception. This also shows, I think, that the Wolffian talk of experience is broader than Kant’s mature notion of experience, which does indeed require sensation (see B1, B165–6).

[5] Similarly in the Discourse: “I observed with regard to logic that syllogisms and most of its other techniques are of less use for learning things than for explaining to others the things one already knows” (AT 6:17, CSM I:119).

[6] This means Descartes could agree with Wolff that the first thing we perceive in our souls is that we are conscious of things as outside us (see p. 106).

[7] My own view is that Kant’s views are consistent, and are best read as involving a standing metaphysical commitment to the self (but not a commitment to the intrinsic nature of that self). I want to grant, though, that some passages from the A Paralogisms chapter are naturally read in a non-metaphysical way.

© Colin Marshall, 2015.

Colin Marshall obtained his Ph.D. from New York University in 2010 and is Assistant Professor at the University of Washington, Seattle, since 2013. He specializes in modern philosophy (Spinoza, Hume) and Kant, as well as metaethics. His latest Kant-related work has been published in Journal of the History of Philosophy, Kant-Studien, and the Philosophical Quarterly.