tried to show that this deprives the assertion of its meaning. But there is also a legitimate use of the words mind and matter, or soul and body or mental and physical. There is for, instance, perfectly good sense in my words when I say: "I am suffering from mental and from physical pain" although it may not be an easy task to get a perfectly satisfactory insight into the meaning of such a sentence. Without going into details, for which we have no room here, we know beforehand that the words Mind and Body, when used legitimately must in some way indicate different logical structures, and we may hold that the difference between these structures must reveal itself somehow — or rather, is nothing but — the difference between the logical form of propositions belonging to psychology and of propositions belonging to physical science. (In other words: there are two languages differing in the rules of logical grammar which for the sake of convenience, we prescribe for them, words of which they are formed. The difficulties of the so-called psychological problem arise from a careless confusion of the two languages. You cannot use different rules of grammar incompatible with each other, in one and the same sentence without speaking nonsense.)
Thus, if we use the word Mind in its nonmetaphysical meaning and substitute this in the idealistic phrase, the assertion that everything in the world is essentially mental becomes: "All real facts can be expressed in psychological language". This is a very vague statement because the language of psychology, owing to the primitive state of this science, is exceedingly fragmentary, and the rules of its grammar are rather ill-defined; nevertheless it is a statement from which special verifiable propositions can be derived, empirical propositions which can be tested by observation. Experience, as far as I am aware, does not afford us any reasons to believe that the structure of all physical laws is the same as that of psychological laws, so that the language of the latter could conveniently be used for the expression of the first. On the other hand a great deal of empirical evidence seems to support the statement resulting from the transformation of the "materialistic" thesis that there are no limits to the applicability of the language of physics. It does seem to be true that all facts and events without exception have a logical form which lends itself to an expression by means of physical concepts. Experience seems to show that any process which we usually represent by psychological phrases employing terms like: feeling,
