Idealism Workshop: Moore

In his paper, "Vats, Sets and Tits", Adrian Moore explored some of the relations between Putnam's proof that we could not be brains in vats, a certain form of scepticism concerning set theory, and a radical form of transcendental idealism. An appealing response to Putnam's original argument is to claim that it answers one kind of scepticism only to leave us with another - the worry that we cannot tell whether our thoughts are limited to our "phenomenal bubble" (a limited aspect of how things are). But this kind of scepticism can be answered, thinks Adrian, by pointing out that for the subject to describe his phenomenal bubble as failing to encompass all the things there are, he has thereby thought about all the things there are. One way to respond to this is to move to a radical form of transcendental idealism according to which we can achieve some kind of inexpressible insight into the possibility that my thoughts are only answerable to my phenomenal bubble.

But the existence of such an inexpressible insight does not vindicate transcendental idealism, at best it indicates that for all I know transcendental idealism may be true. As Wittgenstein pointed out, as soon as we try to draw the limits of the thinkable, we will fail (by thinking the supposedly unthinkable). Thus we cannot think of any insight we may have as the insight that our thinking is only answerable to the phenomenal bubble. In this way, we should resist the move to radical transcendental idealism.

In discussion a number of different issues came up. One was how we should think of the Cartesian dreaming hypothesis in relation to the various types of scepticism discussed. Another was whether we should accept that the brain in Putnam's vat can have thoughts at all, since it seems that he would be unable to think about (genuine) propositions, and that looks as though it may be a condition of the possibility of thought. Finally, there is the question as to what conception of thought is being assumed in the Wittgensteinian denial of the possibility of drawing a limit to thought. Might not some "thick" conceptions of what thought about an object requires block such a move?