Notes by Rush Rhees after a conversation: summer 1942

When we are studying psychology we may feel there is something unsatisfactory, some difficulty about the whole subject or study – because we are taking physics as our ideal science. We think of formulating laws as in physics. And then we find we cannot use the same sort of ‘metric’, the same ideas of measurement as in physics. This is especially clear when we try to describe appearances: the least noticeable differences of colours; the least noticeable differences of length, and so on. Here it seems that we cannot say: ‘If A = B, and B = C, then A = C’, for instance. And this sort of trouble goes all through the subject.

Or suppose you want to speak of causality in the operation of feelings. ‘Determinism applies to the mind as truly as to physical things.’ This is obscure because when we think of causal laws in physical things we think of experiments. We have nothing like this in connexion with feelings and motivation. And yet psychologists want to say: ‘There must be some law’ – although no law has been found. (Freud: ‘Do you want to say, gentlemen, that changes in mental phenomena are guided by chance?’) Whereas to me the fact that there aren't actually any such laws seems important.

Freud's theory of dreams. He wants to say that whatever happens in a dream will be found to be connected with some wish which analysis can bring to light.