into account, on empirical grounds, the probability of its colour having changed in the meantime; 2) comparing my present judgment with a description. I wrote down during the first observation; 3) comparing it with the descriptions given by other people.
The criterion of the truth of the judgment is the agreement of all these different propositions; and if we say that the colour is truly the same, that my memory has not deceived me, we mean nothing but that there is this formal agreement between the descriptions based on memory and on observation. This is entirely a matter of structures; we cannot speak of a repetition or comparison of "content".
If we knew of a case in which there were nothing else with which the judgment of our memory could be compared, we should, in this case, have to declare it impossible to distinguish between a trustworthy and a deceptive memory; we therefore could not even raise the question whether it was deceptive or not: there would be no sense in speaking of an "error" of our memory. It follows that a philosopher would be uttering a meaningless question if he were to ask: "Is it not possible that the colour I am seeing now seems to me to be green, while actually it is red?" The sentence "I am seeing green" means nothing but "there is a colour which I remember has always been called green". This recollection, this datum of my memory, is the one and only criterion of the truth of my statement. I recall it so, and that is final; in our supposed case I cannot go on asking: do I remember correctly ? for I could not possibly explain what I meant by such a question.
Thus we see that the question "is the green I see to-day the same colour as the green I saw yesterday?" refers only to the structure of our expressions and not to some content "green" which is supposed to be beyond. Sameness, equality cannot be predicated of content any more than anything else can be predicated of it; and the case of "two data of consciousness in the same mind at different times" forms no exception.
14. Meaning and verification.
In the preceding arguments we have often made use of the principle that the meaning of a statement can be given only by indicating the way in which the truth of the statement is tested. What is the justification
