SENSATIONS AND BLOOD PRESSURE
BEGINNING AT §256 of the Philosophical Investigations, Wittgenstein is pondering the case of a man who has no 'natural expression' for his sensations, but only has the sensations. In §258 he supposes that, to keep a diary of the recurrence of a certain sensation, this person associates it with the sign 'S', and writes this sign in a calender for every day he has the sensation. Wittgenstein notes a number of awkward features of this supposition, but nothing very clearly ruinous, and then considers this possibility:
270. Let us now imagine a use for the entry of the sign 'S' in my diary. I discover that whenever I have a particular sensation a manometer shows that my blood pressure rises. So I shall be able to say that my blood pressure is rising without using any apparatus. This is a useful result. And now it seems quite indifferent whether I have recognised the sensation right or not. Let us suppose I regularly identify it wrong, it does not matter in the least. And that alone shews that the hypothesis that I make a mistake is mere show. . . .
And what is our reason for calling 'S' the name of a sensation here? Perhaps the kind of way this sign is employed in this language game. -- And why 'a particular sensation', that is, the same one every time? Well, aren't we supposing that we write'S' every time?
There is something incoherent about this case, at least the way it is presented. One can hardly say 'I discover that whenever I have a particular sensation . . .', and then go on to say or imply that it does not matter whether I have that particular sensation. That cancels the supposed discovery; and not only that, it leaves us mystified why Wittgenstein should so confidently say, as if the point were perfectly obvious, that it is quite indifferent whether I have recognised the sensation