Kant's Critical Project

In these notes I give a more extensive overview of some of the central features of Immanual Kant’s “Critical” philosophy“ than I did in the previous notes. We’ll still have only a sketch, but at least the basic parts of Kant’s theory of cognition should attain some clarity.

Immanuel Kant (1724–1804) was the most significant German philosopher of the eighteenth century, and was a key figure in the Enlightenment. He wrote most of his most famous philosophical works relatively late in his professional life, having only achieved a position as full professor in 1770, at the age of forty-six.¹ From 1781 to 1798 Kant published a series of tremendously influential philosophical works, including the Critique of Pure Reason (1781/7), the Groundwork of the Metaphysics of Morals (1785), the Metaphysical Foundations of Natural Science (1786), the Critique of Practical Reason (1788), and the Critique of the Power of Judgment (1790).

We’ll be focusing on two key areas of Kant’s philosophical corpus. The first concerns the metaphysical and epistemological doctrines forming the core of Kant’s mature philosophy, as presented in the Critique of Pure Reason of 1781/87. The second concerns the basic principles of Kant’s moral philosophy in his Groundwork of the Metaphysics of Morals of 1785. The moral philosophy is founded upon the important metaphysical and epistemological positions articulated in the first Critique so that is we shall begin.

1 The Project of the Critique of Pure Reason

There are certain aspects of Kant’s project in the CPR there which should be very familiar to anyone versed in the debates of seventeenth century European philosophy. For example, Kant, like Locke and Hume, wishes to articulate the nature and extent of human knowledge, and to do so in a manner which proceeds from an analysis of the nature of human cognitive capacities. Kant believes that human reason requires a ’critique’ or examination as to whether it is fit to provide us with knowledge. Kant ultimately argues that human reason is not fit to provide us with knowledge of a mind-independent reality transcending human experience. In this sense Kant is deeply sympathetic with ’empiricist’ critiques by Locke, Berkeley, and Hume of ’rationalist’ philosophers such as Descartes and Leibniz.²

However, Kant also argues that we have much deeper and more extensive knowledge of the world we experience (or could possibly experience) than his empiricist predecessors would allow. For example, Kant argues that we have knowledge of necessary truths concerning aspects of the empirical world (such as that every event in the empirical world has a cause), as well as truths which are universal in extent. Thus Kant articulates a view that is directly opposed to the kinds of skeptical arguments Hume discusses in his Treatise and first Enquiry.

Kant thus thinks that we have knowledge of the empirical world governed by necessary and universal laws, while nevertheless being almost wholly ignorant of the fundamental reality which underlies or grounds the existence of the empirical world. In this way Kant combines various aspects of both the traditional rationalist and empiricist positions. Like Locke and Hume, Kant thinks we must realize that the boundaries of human knowledge stop at experience, and thus that we must be extraordinarily circumspect concerning any claim made about how reality is like independent of all human experience. But, like Descartes and Leibniz, Kant thinks that central parts of human knowledge nevertheless exhibit characteristics of necessity and universality, and that, contrary to Hume’s skeptical arguments, we can have good reason to think that they do.

Kant thus critiques pure reason in order to show its nature and limits, and thereby curb the pretensions of various metaphysical systems articulated on the basis of a firm faith that reason alone allows us to scrutinize the very depths of reality. But Kant also argues that the legitimate domain of reason is more extensive and more substantive than previous empiricist critiques had allowed. In this way Kant salvages much of the prevailing Enlightenment conception of reason as an organ for knowledge of the world.

Below I characterize some of the central aspects of Kant’s epistemological framework and how that framework significantly revolutionized our understanding of the possible nature and extent of human knowledge.

2 Two Kinds of Knowledge

2.1 Leibniz

Gottfried Wilhelm Leibniz (1646-1716) was the most significant German philosopher of the seventeenth century. One of the central notions in Leibniz’s philosophy is that the logical structure of our thought mirrors the real structure of reality. Leibniz thus thinks that there are close connections between the nature of truth and the nature of substance. For example:

• All truth is analytic truth by virtue of containment³

  • in every true predication the concept of the predicate is contained in the concept of the subject

• Substance is the ultimate subject of predication, and that which cannot be predicated of anything else

• If x is a substance then there is a concept of x that contains all true predications concerning x⁴

  • finite beings grasp truths about substances via partial grasp of their complete concept
  • God knows all truths about all substances via a perfect grasp of their complete concepts

Take, for example, the historical figure Julius Caesar. According to Leibniz, the statement ’Caesar crossed the Rubicon in 49 BC’ is analytically true. An ’analytic truth’, for Leibniz, is a truth whose predicate does not, in some sense, go beyond what is given in stating the subject. There are obvious ’stutter’ examples of this — ’all red squares are red’ is analytically true since the predicate is so clearly part of the subject. But the same phenomena can occur covertly. For example, the statement ’Bachelors are unmarried men’ is analytically true because part of what it is to be (or for the word ’Bachelor’ to mean) a bachelor is to be an unmarried man.

Leibniz thinks that all truth is analytic. So with our initial example statement ’Caesar crossed the Rubicon in 49 BC’, Leibniz thinks that the relation between the subject (’Caesar’) and the predicate (’crossed the Rubicon in 49 BC’) is relevantly similar to the relation in the case of the ’bachelor’ example. For any individual substance, Leibniz thinks there is a singular concept which picks it out and which ’contains’ all the predicates of the substance (past, present, and future) in just the same way that ’bachelor’ contains ’is an unmarried man’.

Thus, if the world is the totality of individual substances, God possesses a concept of each individual substance, and knows everything that is, has been, or will be true of that individual. This is discussed by Leibniz mostly clearly in his Discourse on Metaphysics (see §§8-16).

2.2 Hume

David Hume (1711-1776) was one of the major figures of the so-called ’Scottish Enlightenment’, which centered around Edinburgh. Kant credits a reading of Hume around 1769 with awakening him from his ’dogmatic slumbers’ and instigating him to develop the metaphysical and epistemological doctrines of the first Critique. It is likely that Kant’s reading of Hume was based on excerpts from Hume’s 1748 work, An Enquiry Concerning Human Understanding. Section 4 of the Enquiry introduces what is now known as ’Hume’s Fork’. This is the division of all reasoning into two categories—viz. relations of ideas and matters of fact.⁵ Hume argues that certainty, justification independent of experience, and knowledge of necessity cannot be had with respect to anything in the empirical world.

2.2.1 Relations of Ideas

Hume describes the knowledge we have by means of perceiving relations between ideas as such that it can be had

by the mere operation of thought, without dependence on what is anywhere existent in the universe. Though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retain their certainty and evidence. (E IV.i.1)

Knowledge of relations between ideas is certain, necessary (its denial entails a contradiction), universal, and justified independently of any experience. Hume thinks that all our knowledge of mathematics and logic falls into this category. Importantly, according to Hume such knowledge gives us no insight into how things actually are in the empirical world. That is the cost of our being able to have such knowledge purely by thinking.

Using Leibniz’s terminology, Hume is arguing that knowledge of relations between ideas is analytic and a priori. Moreover, Hume is giving a reductive account of the a priori in terms of relations between ideas. His explanation of how it is that we can know the truth of some proposition a priori, is that the truth depends on a relation between the ideas constitutive of the proposition (e.g. All red things are red; All bachelors are unmarried), and that we can know the propositions are true simply in virtue of possessing the relevant ideas.

However, Hume and Leibniz radically disagree concerning the extent of analytic truth and our a priori knowledge. Recall that Leibniz construes all truth as analytic, in the sense that all truth depends on the predicate’s being ’contained’ in the subject. So, for any true judgment, there is in principle an analysis of the subject concept in which it can be shown that the predicate of the judgment is part of (or ’contained in’) the subject’s complete concept. Hume, in contrast, has no robust theory truth (at least in a sense which Leibniz would recognize), and certainly does not attempt to explain all truth in terms of containment. The reason we have a priori knowledge of relation of ideas is because we (i) have privileged access to those ideas, and (ii) the knowledge we have of relations between ideas is parasitic on our knowledge of the meanings or content of the ideas, and not anything else. Hence one can know that all triangles have three sides is true and necessarily so, just in virtue of knowing what ’triangle’ means.

2.2.2 Matters of Fact

In contrast to knowledge of relations between ideas, Hume argues that our knowledge of matters of fact is contingent (its denial is not a contradiction), local, uncertain, and dependent for its justification on empirical inquiry. Examples of knowledge of matters of fact include such propositions as the number of houses on one’s street, the names of one’s parents, the identity of the current President of the United States, and the atomic weight of gold. Knowledge of all of these propositions requires that we consult how things actually are in the world. In none of these cases can we earn the knowledge merely by thinking.

In the terminology of Leibniz and (after Hume) Kant, knowledge of matters of fact is synthetic and a posteriori. It is justified only by current or past experience and cannot be attained purely by any process of conceptual analysis. Hume is thus taking up a diametrically opposed position to that of Leibniz, who argued that knowledge of empirical matters of fact can be obtained via conceptual analysis of the complete concepts of the substances constituting the actual world. It may be the case that we cannot complete such an analysis, but one is in principle available (to God).

Hume’s fork results in the position that there is no substantive knowledge of the empirical world that we can have via analysis of our ideas (i.e. our concepts) alone. All empirical knowledge including, e.g. knowledge in the physical sciences, is knowledge of matters of fact, and is thus contingent, local, and uncertain. Hume attempts to drive this conclusion home by arguing that the process of reasoning by means of cause/effect relationships has no ultimate rational basis, and thus cannot give us knowledge of how things are beyond our current or remembered experience. We’ll turn to an examination of that argument now.

3 Kant on the A Priori

We’ve seen that several philosophers argue that there are kinds of knowledge that may be had just by thinking, or are universal and necessary in scope. Hume’s conception of knowledge made this especially clear. According to Hume, knowledge of necessary and universal truths must be a function purely of knowledge of the relations of ideas.

Kant agrees with Hume that a priori knowledge is independent of experience. In fact, he sees it as definitive of ’pure’ a priori knowledge that it be completely independent of experience. He contrasts such knowledge with ’empirical’ knowledge or knowledge a posteriori. A priori knowledge may be more or less ’pure’ according to whether or not the concepts which make it up are themselves a priori knowable. Kant uses the example ’ever alteration has a cause’ as an example of impure a priori knowledge, since the concept <alteration> is empirical.

One important point about Kant’s use of ’independence’ in describing the a priori. Kant does not think that a priori knowledge is independent of experience in the sense that one need have no experience in order to have the knowledge. On the contrary, Kant thinks that all of our knowledge depends on our having experience of some kind or another, though he doesn’t think this dependence entails that all our judgments are ultimately justified by experience. This is why Kant says that

although all our cognition commences with experience, yet it does not on that account all arise from experience. For it could well be that even our experiential cognition is a composite of that which we receive through impressions and that which our own cognitive faculty (merely prompted by sensible impressions) provides out of itself, which addition we cannot distinguish from that fundamental material until long practice has made us attentive to it and skilled in separating it out. (B1-2)

There seems to be two reasons for Kant’s thinking this. First, we need experience in order for our cognitive faculties to function and develop. Second, we may need particular experiences in order to acquire certain concepts (e.g. red experiences in order to acquire the concept <red>). This is what distinguishes pure from impure a priori judgments. Impure a priori judgments are partially constituted by concepts which themselves must come from experience.

If a priori knowledge is, for Kant, knowledge that is (in some sense to be further specified) independent of experience, that fact is not the only mark or indicator that some bit of knowledge is a priori. In addition, Kant argues, any bit of knowledge that is necessary and/or universal in scope is itself a priori.

Experience teaches us, to be sure, that something is constituted thus and so, but not that it could not be otherwise. First, then, if a proposition is thought along with its necessity, it is an a priori judgment; if it is, moreover, also not derived from any proposition except one that in turn is valid as a necessary proposition, then it is absolutely a priori. Second: Experience never gives its judgments true or strict but only assumed and comparative universality (through induction)…Necessity and strict universality are therefore secure indications of an a priori cognition (B3-4)

Kant argues that the conception of a priori knowledge is presupposed in many empirical judgments as well as in particular sciences. He specifically points to mathematics (’5+7=12’) and to physical judgments (’every alteration has a cause’). One of Kant’s arguments (which he hints at in §III of the Introduction) is that all of our empirical knowledge (even that knowledge which we think we have unproblematically) presupposes a priori knowledge.

Kant thinks that there are many examples of judgments which we claim to know a priori, but he is interested primarily in a specific subset of those which constitute the subject matter of metaphysics—viz. judgments concerning God, the soul (or mind), and immortality. One of Kant’s primary aims is to determine whether metaphysical knowledge of such things is possible, and if it is possible, what the extent and nature of that knowledge might be. Metaphysical knowledge is problematic, Kant argues, because unlike other forms of a priori knowledge, such as logic and mathematics, it is not at all obvious which metaphysical judgments are in fact correct and thus known, and which are merely thought to be so. This is exemplified, Kant thinks, by the contentious disputes in which philosophers have long been involved. Kant thus hopes that, by giving a critique of reason, he can demonstrate the extent to which metaphysics might count as a science, and thus rest on a secure set of claims.

3.1 The Analytic/Synthetic Distinction

A judgment is known (or knowable) a priori if it is known independently of experience. Kant thinks that this is not the only dimension according to which one can analyze a judgment. Kant argues that all judgments, in addition to being classifiable as either a priori or a posteriori (or empirical), may also be classified as being either analytic or synthetic.

An analytic judgment is, according to Kant, one in which the predicate is ’contained’ in the concept. One way of understanding this notion of ’containment’ is via a claim about meaning. Accordingly, analytic judgments are those whose truth is known merely in virtue of knowing the meanings of the concepts constituting the judgment. For example, in the judgment ’All bachelors are unmarried’ the concept <unmarried> is part of the meaning of <bachelor> and so the truth of the judgment is grasped just by knowing the relevant meanings.

Kant also introduces several other markers of analyticity, four in total. He says that in an analytic judgment

1. The predicate is ’contained’ within the subject (A6-7/B11)
2. The predicate is ’identical’ with the subject (A7/B11)
3. Analytic judgments are ones which are ’explicative’ rather than ’ampliative’ (A7/B11)
4. Analytic judgments are those knowable by means of application of the principle of non-contradiction (A151/B190)

Which, if any of these markers is best thought of as the main characteristic of an analytic judgment? This is a disputed issue (cf. @anderson2005; @proops2005), though certainly, in all cases Kant is thinking of ’atomic’ judgments of subject-predicate form.

3.1.1 Containment Analyticity

Kant defines analyticity in terms of containment this way:

the predicate B belongs to the subject A as something that is (covertly) contained in this concept A (A6/B10)

Kant distinguishes two distinct notion of logical containment—viz. the “content” and the “extension” of a concept. These notions are ’intesional’ they concern what is thought ’in’ the concept and not what objects fall under the concept (this would be, for Kant, a non-logical notion of ’extension’). The content of a concept is the group of intensional concepts (marks) that it “contains in” itself as components, whereas the concept’s logical extension comprises the group of lower, or more specific, concepts it “contains under” itself (Jäsche Logic, 9:95–7, esp. §§ 8, 9, 11).⁶ Kant conceives of concept individuation along the broadly Aristotelian lines of a logic of terms. Concepts (or terms) fall under some general genus and are distinguished from other concepts falling under the genus in terms of specific differentia. For example, the concept <human> falls under the genus <animal> and is distinguished from other animals by its differentia—viz. <rational>.

Divisions are exclusive and exhaustive disjunctions of everything that falls under the genus.⁷ Thus two points apply:

1. The division of a genus is complete — the various species of a genus, taken together, exhaust the genus.
2. Membership in a species is exclusive — no species may be predicated of another.

Content and extension are related to one another reciprocally. If we conceive of concepts as organized hierarchically, as on a Porphyrian Tree, then the content of a concept A is everything above it in the concept hierarchy (i.e. every concept which constitutes A) and the extension of the concept is everything below it in the hierarchy (i.e. every concept which contains A as a proper part).

Kant also holds that,

In regard to the logical extension of concepts, the following universal rules hold 1. What belongs to or contradicts higher concepts also belongs to or contradicts all lower concepts that are contained under those higher ones; and 2. conversely: What belongs to or contradicts all lower concepts also belongs to or contradicts their higher concept. (Jäsche Logic, 9:981)

This means that concept with the same logical extension must contain the same conceptual ’marks’ as content. They also must exclude the very same marks that ’contradict’ the content or extension of the concept. Kant calls concepts that share the same content and extension in this way ’convertible’ or ’reciprocal’ concepts [/Wechselbegriffe/] (JL 9:98, also 24:261, 755, 912).⁸

The rules of division thereby guarantee that the concepts constituting the content of a further concept are all completely distinct from one another ( i.e. they occupy different points on a Porphyrian hierarchy). Thus, for one concept to ’contain’ another is to have that concept as a member of its extension in a strict hierarchical ordering of genus/species relationships where concepts are distinguished according to their (non-overlapping) differentia. Conceptual analysis then involves an explication of the conceptual marks constituting the content of a concept sufficient for locating it at a specific place in some such hierarchy. The rules of conceptual division are thus sufficient for guaranteeing that hierarchy encodes only analyticities.

Any attempt to build a science via conceptual analysis would thus be an attempt to construct a complete logical ordering of concepts according to the division rules explained above. Such a division would make the inferential relationships between concepts totally transparent, and thus provide a totally clear and demonstrative science of whatever subject matter was considered fit for analysis. So Kant’s denial, in his critical philosophy, that conceptual analysis provides us with any substantive knowledge of reality is best understood as denying that the explication of conceptual hierarchies via logical division provides us with substantive knowledge. One of Kant’s key insights was that at least some of our knowledge has an importantly non-logical basis. For example, as we will see, the traditional logic of concepts lacks the expressive power necessary to represent our knowledge of mathematics (arithmetic and geometry) and Kant took this fact as a significant reason in favor of his view that we must therefore have synthetic a priori knowledge.⁹

3.1.2 Problems

3.2 The Synthetic A Priori

Kant argues, in ways similar to Locke, Hume, and Leibniz, that analytic judgments are knowable a priori. Staying with the ’containment’ metaphor, since the predicate is contained in the subject of an analytic judgment, there is no need to look beyond the judgment to the world (so to speak) in order to determine the truth value of the judgment. In this Kant is obviously in agreement with Locke, Hume, and Leibniz. Kant agrees with his empiricist predecessors in claiming that all a posteriori judgments are synthetic. Since the predicate is adding something new to the subject we must look beyond the judgment to the world—what we can experience—in order that we might determine the relevant judgments truth or falsity.

Kant’s main innovation to the a priori/posteriori and analytic/synthetic schemas is to note that the analytic a priori and the synthetic a posteriori do not exhaust the realm of possible judgments. There are also synthetic a priori judgments that are possible. Kant argues that causal judgments are a clear example.

Take the proposition ’Everything that happens has its cause’…the concept of of a cause lies entirely outside [the concept of event] and indicates something different than the concept of what happens in general, and is therefore not contained in the latter representation at all. How then do I come to say something quite different about that which happens in general, and to cognize the concept of cause as belonging to it, indeed necessarily, even though not contained in it? What is the unknown =X here on which the understanding depends when it believes itself to discover beyond the concept of A a predicate that is foreign to it yet which it nevertheless believes to be connected with it? (A9/B13)

Kant argues here that our judgments concerning events presuppose that they do not just occur but are caused to occur, that we know this to be true necessarily and universally, and that we have no explanation of this fact unless the judgments we make in such cases are synthetic a priori judgments. The question remains, however, just how such synthetic a priori judgments could be possible. What is it that could link the concepts in a subject-predicate judgment such that the truth of the judgment holds necessarily and universally, while its nevertheless being true that the predicate is not contained in the subject of the judgment, and thus that the judgment is not analytic?

Kant argues that we need to explain how synthetic a priori judgments are possible, and that the explanation of the possibility of significant portions of our knowledge rests on this, including mathematics and natural science, as well as the very possibility of metaphysics.

3.3 Mathematics and the Synthetic A Priori

Recall that for Hume, mathematical knowledge was a function merely of knowledge of relations of ideas, in other words, that math is analytic and a priori. Kant disputes this. Our mathematical knowledge is certainly a priori, he thinks, but it is not explained in terms of relations of ideas or concepts (i.e. in terms of containment or any of the other marks of analyticity). Instead, Kant argues that mathematical knowledge must be synthetic, but since it is necessary and universal, also a priori.

Mathematical judgments are all synthetic. This proposition seems to have escaped the notice of the analysts of human reason until now, indeed to be diametrically opposed to all of their conjectures, although it is incontrovertibly certain and has very important consequences. (A10/B14)

Kant uses two examples in his argument concerning mathematics. The first is the judgment ’7+5=12’ and the second is the geometric judgment that ’the shortest distance between two points is a straight line’. Though both judgments are knowable a priori, Kant thinks that in neither of these two cases, can we explain the truth of the judgments analytically.

one might initially think that the proposition “7 + 5 = 12” is a merely analytic proposition that follows from the concept of a sum of seven and five in accordance with the principle of contradiction. Yet if one considers it more closely, one finds that the concept of the sum of 7 and 5 contains nothing more than the unification of both numbers in a single one, through which it is not at all thought what this single number is which comprehends the two of them. The concept of twelve is by no means already thought merely by my thinking of that unification of seven and five, and no matter how long I analyze my concept of such a possible sum I will still not find twelve in it. One must go beyond these concepts, seeking assistance in the intuition that corresponds to one of the two… . (B15)

Kant’s argument here is that while it might be analytically true that the sum of 7 and 5 is a number (and also that it must be a natural number), it is not clear from analysis alone that the sum is equal to 12, or any other pair of natural numbers which might sum to 12.

Kant seems to think that to the extent one finds the answer twelve obvious one is adverting, either explicitly or implicitly, to some particular experience of adding units, such as counting on one’s fingers, or adding up objects (e.g. apples, chairs, blocks, etc.).

Also, if ’7+5=12’ is known analytically, then in thinking it one is equivalently thinking of any or all the numbers which are equal to 12, including very large numbers (e.g. any numbers m and n which might yield 12). This certainly doesn’t reflect our experience when calculating such sums, which may yield further evidence that the judgment isn’t analytically true.

4 Kant’s ’Copernican Revolution’

In a famous passage Kant compares his critical philosophy to the central contribution of Nicolas Copernicus.

Up to now it has been assumed that all our cognition must conform to the objects; but all attempts to find out something about them a priori through concepts that would extend our cognition have, on this presupposition, come to nothing. Hence let us once try whether we do not get farther with the problems of metaphysics by assuming that the objects must conform to our cognition, which would agree better with the requested possibility of an a priori cognition of them, which is to establish something about objects before they are given to us. This would be just like the first thoughts of Copernicus , who, when he did not make good progress in the explanation of the celestial motions if he assumed that the entire celestial host revolves around the observer, tried to see if he might not have greater success if he made the observer revolve and left the stars at rest. (Bxvi–xvii)

So just as Copernicus sought to explain the apparent motions of objects in the heavens in terms of the movement of the earthbound observer, so too Kant attempts to account for the apparently characteristics of objects in terms of our cognitive faculties and the cognitive conditions under which we know the objective world. In Kantian phrase, instead of assuming that our knowledge of the object must conform it it, we assume that it conforms to our knowledge.

4.1 Transcendental Idealism

Kant’s name for the position he articulates according to which objects must conform to our way of knowing them ’Transcendental Idealism’. Though the exact meaning of Transcendental Idealism is much disputed by Kant’s interpreters, it is clear that he intends at least two things by it.

First, according to Transcendental Idealism, space and time are neither independent subsisting entities (as was suggested by Newton), nor object-dependent orders of relations between entities (as was argued by Leibniz). Instead, they are mind-dependent ’forms of intuition’. They are the characteristic ways in which we experience things rather than independent things that we experience, or relations between things that we experience. Space and time are ’empirically real’ — they are fundamental features of the empirical world that we experience. But they are not real ’in themselves’. They have no ultimate reality apart from subjective experience.

Second, in addition to the transcendental ideality of space and time, to which all experienced objects must conform, Kant argues that empirical reality is itself structured by a privileged set of a priori concepts.

Yet because I cannot stop with these intuitions, if they are to become cognitions, but must refer them as representations to something as their object and determine this object through them, I can assume either that the concepts through which I bring about this determination also conform to the objects, and then I am once again in the same difficulty about how I could know anything about them a priori, or else I assume that the objects, or what is the same thing, the experience in which alone they can be cognized (as given objects) conforms to those concepts, in which case I immediately see an easier way out of the difficulty, since experience itself is a kind of cognition requiring the understanding, whose rule I have to presuppose in myself before any object is given to me, hence a priori, which rule is ex- pressed in concepts a priori, to which all objects of experience must therefore necessarily conform, and with which they must agree. (Bxvii-viii)

Kant here argues that the object which appear to one in perceptual experience, or ’intuition’ as he calls it, also must conform to our basic conceptual scheme. He explains what he means here in the last sentence: objects must conform to our conceptual scheme because that scheme makes possible the experience of them.

We’ll discuss Kant’s ’Copernican’ strategy here in another class. However, the basic idea is that Kant will show that what makes synthetic a priori knowledge possible is the structure of our cognitive faculties including the pure forms of intuition and a privileged set of a priori concepts. These forms and concepts jointly make experience possible and allow us to draw inferences that hold with necessity and universality concerning objects encountered in experience. What’s more, Kant argues that because a priori concepts are necessary for experience in general, we can know that those concepts are applied legitimately, since he is taking it as obvious that we have experience. While we won’t have time to explore all of Kant’s arguments for this position, we will explore one—viz. his argument that we can know with certainty that, in opposition to Hume, necessary causal connections really hold between distinct objects or events, and thus that lawful scientific knowledge of objects is possible.