The Evolution of Modern Metaphysics: Making Sense of Things (30 page)

As we shall see, most of what Kant is offering here will later be rejected. Some philosophers will reject his very dichotomies.
¹⁹
Others will accept the dichotomies but reject his application of them, claiming, for instance, that arithmetical truths are analytic.
²⁰
Some
of what Kant is offering will
suffer a fate that is unusual for philosophical ware: it will be decisively refuted (notwithstanding a few brave attempts to salvage it by creative reinterpretation
²¹
). Thus twentieth-century advances in science will show that some of his purported examples of synthetic
a priori
knowledge, so far from being that, are not even examples of knowledge. Nay, the things that are said to be known are not even
true
. (Between two points there can be more than one straight line.
²²
This is a fact about physical space. But let no one deny that it is physical space that Kant is talking about, too (A157/B196 and A163/B204).) Moreover, the fact that these scientific advances will be made partly through experimentation means that not only will those particular examples be discredited, but the
a priority
of other examples will be called into question. Geometry, by the twentieth century, will seem a decidedly empirical discipline.
²³

Fortunately, the importance of Kant’s doctrines does not depend on their detailed truth. It does not even depend on their broad truth. Kant may be fundamentally wrong. But if he is, his errors are of that deep sort that can still instruct us, prompt us, stimulate us, and guide us, opening up significant new possibilities for us to explore. If we prescind from the objections to his doctrines, as we
pro tempore
must if we are properly to learn from them, then one significant possibility that they immediately open up is the following: just as mathematics can be seen as the pursuit of synthetic
a priori
knowledge, so too can metaphysics. That is, in the most general attempt to make sense of things, success may accrue from following a method that consists,
contra
Hume, neither in conceptual analysis nor in empirical investigation.

4. How Synthetic
A Priori
Knowledge Is Possible: Transcendental Idealism

Before we can so much as consider that possibility, however, we need to address the following fundamental Kantian question, on which his entire critique turns: how is synthetic
a priori
knowledge possible (B19)? In raising this question Kant is not having second thoughts about whether it is possible. Throughout his discussion he stands by his various arguments
that mathematical knowledge fills the bill. A philosophical sceptic might caution, ‘Provided there is such a thing as mathematical knowledge.’ But that is not a proviso that Kant ever feels the need to add. He takes it to be a kind of datum that there is such a thing as mathematical knowledge (B20–21 and
Prolegomena
, 4:327).
²⁴
He also takes for granted that any non-trivial knowledge that deserves to be called ‘metaphysical’ must likewise be both synthetic and
a priori
(B18 and
Prolegomena
, 4:368). His question about the possibility of synthetic
a priori
knowledge is not intended in a sceptical vein then. It is rather intended to serve the following two functions: first, to help us to overcome certain natural assumptions that make synthetic
a priori
knowledge, knowledge that is both substantive in some robust sense and yet independent of experience, seem impossible; and second, concomitantly, to give us a grasp of what the scope and limits of synthetic
a priori
knowledge are, so that we can decide whether such knowledge is possible, in particular, in metaphysics. ‘That metaphysics has until now remained in such a vacillating state of uncertainty and contradictions,’ Kant observes, ‘is to be ascribed solely to the cause that no one has previously thought of this problem…. On the solution of this problem, or on a satisfactory proof that the possibility that it demands to have explained [sc. the possibility of synthetic
a priori
knowledge in metaphysics] does not
in fact exist at all, metaphysics now stands or falls’ (B19; cf.
Prolegomena
, 4:276).

What are the natural assumptions that make synthetic
a priori
knowledge seem impossible? There are two. The first is that synthetic knowledge must answer to what is independent of it.
²⁵
,
²⁶
The second is that it can answer to what is independent of it only if it is empirical (where empirical knowledge – which is roughly what Kant means by ‘experience’ (B147
and 218)
²⁷
– is simply the complement of
a priori
knowledge). More fully and more formally:

The Independence Assumption
: For any item of knowledge
k
, if
k
is synthetic, then there is something
x
such that
x
is independent of
k
and such that
k
answers to
x
.
²⁸

The Experience Assumption
: For any item of knowledge
k
and anything
x
that is independent of
k
,
k
answers to
x
only if
k
is grounded in some sensory effect of
x
, hence only if
k
is empirical.

A Cartesian (among others) would object to the Experience Assumption. An item of
a priori
knowledge, the Cartesian would say, can answer to what is independent of it through God’s benevolent guarantee that the former accords with the latter. But Kant, who leans far enough in the direction of empiricism to be sympathetic to the Experience Assumption – it is on the Independence Assumption that he will eventually mount his attack – would reject this Cartesian view on the grounds that it fails to do justice to the necessity that the knowledge must enjoy if it is to qualify as
a priori
(cf. B167–168). It is almost as if the Cartesian is positing a sixth sense which, where the other five are linked to their objects by (psycho-)physical causal relations, is linked to its objects by Divine ordination.
²⁹
But note that, even if the Cartesian were to concede that he had done that (thereby leaving the Experience Assumption unchallenged), he would still owe us an account of how this link between the sixth sense and its objects enables the former to represent the latter, or, equivalently, how the relation between the item of knowledge in question and the independent reality in question enables the former to answer to the latter. Of course, the Cartesian owes us an account of the second of these anyway. This was the issue to which I drew attention at the end of
Chapter 1
, §5. And although I did not there call for a complementary account of how the (psycho-)physical causal relation enables the other five senses to represent their objects – or equivalently, how relations between items of ordinary empirical knowledge and occurrences in the physical world enable any of the former to answer to any of the latter – in fact there is an issue about that too (cf.
Prolegomena
, §9). We are owed an account of how any purported relation of representation qualifies for that
title. So although Kant has the Independence Assumption in his sights, the very fact that his problem helps to bring these issues to our attention means that he cannot rest content with overcoming the Independence Assumption. He must also motivate the Experience Assumption. He must say what it is about experience that equips it, and it alone, to constitute knowledge of an independent reality. The question, ‘How is synthetic
a priori
knowledge possible?’ thus assumes a much wider significance for Kant. It eventually comes to embrace the question, ‘How is knowledge of an independent reality possible?’, or, more broadly, ‘How is representation possible?’
³⁰

I can scarcely even begin to go into the details of Kant’s extraordinary answers to these questions – or should I say, answer (in the singular)? Part of what is extraordinary about how he addresses the questions is that he has what is in effect a single story to tell in response to all of them. He states a ‘clue to the discovery’ of this story – to borrow a phrase of his from elsewhere (A66/B91) – in the following very well-known passage from the Preface to the second edition of the first
Critique
:

Up to now it has been assumed that all our cognition must conform to the objects…. [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…. 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)

Very roughly, Kant’s story proceeds as follows. When we have knowledge of something that is independent of us, and hence of something that is independent of that knowledge, this is made possible by the fact that we are ‘given’ the thing in question: it affects us in some way (A19/B33; cf. A635/B663).
³¹
And the way in which it affects us is sensory (A19–20/B33–34 and B147). So that is why the Experience Assumption holds. But we can be
affected in this way, or we can be given something in this way, only because we have certain capacities for reception. Through these we ourselves make a contribution to the form and structure of our experience. It is as though we have native spectacles through which we view things. And because these spectacles are native, we can have
a priori
knowledge pertaining to them: we can know,
a priori
, how things must appear through them. Such knowledge is synthetic. For it does not accrue from pure conceptual analysis. On the other hand, given that it is knowledge of the appearances of things, and given that it derives solely from our very capacity for such knowledge, neither does it answer to anything that is independent of it. So it falsifies the Independence Assumption. This means that we have an account of how synthetic
a priori
knowledge is possible,
³²
which is in turn part of an account of how knowledge of an independent reality is possible, which is in turn part of an account of how representation is possible. It is part of an account of how representation is possible because our receptive capacities ensure that we are not just affected by objects but are given them as being a certain way, and hence as capable of being thought to be a certain way, albeit, granted the ‘Copernican revolution’, a way that is determined partly by our spectacles: objects are given to us as appearing thus and so through our spectacles.
³³

Moreover, objects are given to us
only
as appearing thus and so through our spectacles. We cannot take our spectacles off. We cannot have (synthetic) knowledge of ‘things in themselves’. Kant accordingly classifies his position as a kind of idealism. It is a kind of idealism in the sense that the objects of our knowledge, as they are known to us, have a form that depends on the knowledge itself. In Kant’s own words, ‘all objects of experience possible for us … are nothing but appearances,… which, as they are represented,… have outside our thoughts no existence grounded in itself’ (A490–491/B518–519). But this idealism is not a matter of
what
we know about such objects. It is a matter of
how
we know it. (It is not a matter of what we see through our spectacles. It is a matter of our seeing through spectacles at all. For instance, included in what we know about such objects are both of the following: that the sun is larger than the moon, and that the sun’s being larger than the moon
does not depend in any way on our knowing it to be so
. Both of these, however, involve the occupation of space, and, as we are about to see, Kant takes space to constitute part of our spectacles.
³⁴
) Kant accordingly classifies his idealism as ‘transcendental’, where
the word ‘transcendental’ signifies not ‘a relation of our cognition to things, but only to the
faculty of cognition
’ (
Prolegomena
, 4:293, emphasis in original; cf. A11/B25); not our knowledge of objects, but our knowledge of how we know them.
³⁵
Transcendental idealism will hereafter play a crucial role in our narrative.
³⁶

To understand better how radical Kant’s transcendental idealism is, we need to reflect on the nature of our spectacles. Where Hume distinguished
between impressions and ideas, and saw this as a distinction of degree (see §2 of the previous chapter), Kant has a distinction of kind between
intuitions
,
³⁷
whereby we are directly given objects, and
concepts
, whereby we think about objects, as thus given (A19/B33). Intuitions are products of our pure receptivity; there is something passive about them. Concepts are products of our ‘spontaneity’; there is something active about them.
³⁸
Our knowledge, or at any rate our synthetic knowledge, requires both (A50–51/B74–75). And our spectacles involve both. Thus, given that our synthetic
a priori
knowledge includes knowledge of the structure of space and time, Kant concludes that not even these are features of things in themselves, but are rather two
a priori
intuitions that constitute part of our spectacles (A19–49/B33–73).
³⁹
He likewise identifies twelve fundamental
a priori
concepts that he takes to constitute part of our spectacles (A79–80/B105–106).
⁴⁰
Significantly, in the light of some of the difficulties with which Hume wrestled, these concepts include (pure forms of) both the concept of substance and the concept of causality (A80/B106; cf.
Prolegomena
, §27). These twelve concepts serve as a kind of noetic glue. It is by means of them that our intuitions are combined together so as to ensure that we are not just given objects but are given them as being a certain way.