Phil asked:

I’m having a difficult time grasping what exactly is Kant’s ‘Transcendental Unity of Apperception,’ and the role it plays in regaining objectivity in the world since according to him, the only world we can know is one that our minds construct through sensibility, understanding, and judgements.

Answer by Geoffrey Klempner

I’m going to try to give a simple account of Kant’s notion of the Transcendental Unity of Apperception and the role it plays in his philosophy. You are right to be suspicious about the kind of ‘objectivity’ that this theory can account for.

Let’s start with the question: what is the difference between one self and two selves: me and you, for example? Well, you have your thoughts and feelings, and I have mine. You have your body and I have mine. However, it would be logically possible for me to have your body as well as my own, your thoughts and feelings as well as my own. Then we would be looking at the individual, Phil-GK who only appears to others as two separate people.

Or one could consider the possibility that I suffer from a radical form of multiple personality disorder. In which case there would be two individuals, GK1 and GK2 ‘sharing’ my body.

In either case, there are various ways in which one could empirically verify that Phil and GK had ‘fused’ to become Phil-GK, or that the individual known as ‘GK’ is in fact two people, GK1 and GK2.

Science fiction possibilities aside, the point here is that it is in some sense a given, and hence ‘a priori’, or known prior to any empirical verification, that the self is a unity. Even Hume, with his ‘bundle theory’ of the self accepts that at any given time, if ‘ideas’ x and y are in the same bundle, and ideas y and z are in the same bundle, then x and z are in the same bundle.

So what? Descartes famously drew the conclusion that the self is a thinking substance. That’s what it’s identity consists in. This is a fallacy, according to Kant. (He goes to great lengths in showing this in the section of the Critique entitled, ‘Paralogisms of Transcendental Psychology’.) Briefly, the upshot is that the substance theory explains everything and nothing. Maybe GK is two thinking substances, or a hundred thinking substances, and I would never know. Or maybe my thinking substance changes its identity every second, each substance transferring its states to the next substance when it ‘dies’ like a line of colliding pool balls.

Now comes the brilliant part. We want the idea of unity to do some work, otherwise it is just free-wheeling, ‘a knob which turns, although nothing turns with it’ as Wittgenstein says about a similar matter in Philosophical Investigations.

Kant realized that the only way to give a meaningful role for the identity of the self is as a logical constraint on the kinds of experience that are possible. A Cartesian thinking substance can have any kind of ‘experience’, because for Descartes all experience basically is is a series of perceptions spread out in time. But our experience isn’t like this. It is ‘as of’ a world of objects in space.

What if, Kant thought, we simultaneously construct a story of the self and its progress through the world, and a story of the world and the objects in it? The ‘Transcendental Unity of Apperception’ now becomes a logical constraint on what kinds of experience are possible. The dramatic conclusion, which Kant took as to be an answer to the scepticism expressed in Descartes’ First Meditation’, is that experience is only possible if it is experience ‘as of’ a world of objects in space.

The story of a world of objects in space and a self which traces a path through that world is a theory. Raw experience (or ‘intuition’) is evidence for that theory. If it isn’t, then it is not ‘experience’ in any meaningful sense. If I know that I exist, as a subject with an identity, then I know that there exists a world of objects in space (‘Refutation of Idealism’, 2nd. edition).

But what has Kant proved, really? The ‘world’ is a theory. It is my theory. Everything I will ever experience relates to the experience of being a subject in the world. But all this could be true if all that existed, in ultimate reality, was raw experience together with a mysterious power of melding it together into a ‘story of a world’. In other words, you can be a fully fledged solipsist and accept everything Kant says about the necessary existence of an external world.