4.1121 Psychology is no more closely related to philosophy than is any other natural science.
Theory of knowledge is the philosophy of psychology.
Does not my study of sign-language correspond to the study of thought-processes, which philosophers held so essential to the philosophy of logic? Only they got entangled mostly in inessential psychological investigations and there is an analogous danger for my method.
So the work of philosophy is not psychological? Not in the sense of a scientific psychology anyway. But if theory of knowledge, which has dominated philosophy from Descartes through Kant at least, is the philosophy of psychology, then why isn’t psychology closer to philosophy than other sciences? Do other major branches of philosophy correspond to other natural sciences? Surely not. Presumably then the philosophy of psychology is not taken here to be closely related to psychology. Because, despite the obvious relation, it is a wholly different kind of activity. Philosophy is not the science of the mind, or any discipline aimed at producing true propositions about the mind (whatever it might take itself to be aimed at). The inessential and psychological is contrasted here with something else, which I call logical and could be called clarificatory or elucidatory. Old philosophers are also contrasted with Wittgenstein, who presents himself as doing something new. But what is his [new] method? Has he told us? And what is the danger that it faces? Mistakenly mixing metaphysics with logic? Or is that the old danger? Mistaking nonsense for sense? Definitions for facts? Clarifications for discoveries or theories? Perhaps.
Mounce (p. 32): “Psychology is irrelevant to philosophy or logic because it is not a psychological process that gives sense to logical form; on the contrary, it is only logical form that can give sense to a psychological process, that can make it, for example, a genuine thought as opposed to a random succession of images. Thus the psychological activity involved in correlating a mark with an object is in itself entirely meaningless. What gives it a meaning, what makes it a genuine correlation, is the logical structure into which the mark enters.”
Anscombe (pp. 82-86) identifies “Carnap and his school” (p. 86) as people who seem to have fallen into the danger identified here by Wittgenstein.