them; but actually we make no assumptions of any kind, our reasoning does not rest on any presuppositions about the real world. All genuine philosophy (as I shall have to point out later on) moves entirely in the realm of possibilities — possibilities which will, of course, always be suggested by realities, but may be considered quite apart from their realisation.
In our case what we said about the possibility of expression remains perfectly valid in a universe which contains no living being beside myself (we will not discuss the question whether such a universe would be the ideal of a "solipsistic" philosopher); I can express facts to myself and communicate with myself — in fact, I do so every time when I take down something in my note book or commit something to my memory. In reading my note or recalling the remembered fact my present self receives a communication from my former self. My note book and my "memory" are vehicles carrying through time the description of a fact; the description consists of a series of marks whose meaning must be understood, and there is a possibility of misunderstanding and of faulty transmission. The note in my book may have been changed, my memory may deceive me.
You observe that for the essence of communication it makes no difference whether the note book is what the metaphysician would call "a mere dream", or possesses what he might call "objective reality". The marks in it, whether "real" or "imagined" (whatever that may mean) do express something, either correctly or incorrectly.
As soon as we try to ascertain whether a proposition which has thus been transmitted from an earlier self to a later self is true or false we find that the methods We use for this purpose consist in comparing structures and that there can be no mention of content. When I keep in mind the colour of a green object, and to-morrow I am shown another object and am asked whether it has the "same" colour as the first one, my memory will give a more or less definite answer to the question. The question has a good meaning, of course, but can it be said to refer to "sameness of content"? Most certainly not! This follows from the way in which the answer given by memory is tested. For in a certain sense we must admit that our memory may "deceive" us. When do we say that it has done so? If there are methods of testing its judgment, and if all these methods fail to verify it. Such methods are: 1) looking again at the object in question and taking
