great error of mistaking the unique position of the ego, which is an empirical fact, for a logical, a priori truth, or, rather, substituting the one for the other. It is worth while to investigate this matter and analyse the sentence which seems to express the egocentric predicament. This will not be a digression, for without the clarification of this point it will be impossible to understand the basic position of our empiricism.
How does the idealist or the solipsist arrive at the statement that the world, as far as I know it, is 'my own idea', that ultimately I know nothing but the 'content of my own consciousness' ?
Experience teaches that all immediate data depend in some way or other upon those data that constitute what I call 'my body'. All visual data disappear when the eyes of this body are closed; all sounds cease when its ears are stuffed up ; and so on. This body is distinguished from the 'bodies of other beings' by the fact that it always appears in a peculiar perspective (its back or its eyes, for instance, never appear except in a looking glass); but this is not nearly so significant as the other fact that the quality of all data is conditioned by the state of the organs of this particular body.
Obviously these two facts — and perhaps originally the first one — form the only reason why this body is called 'my' body. The possessive pronoun singles it out from among other bodies; it is an adjective which denotes the uniqueness described.
The fact that all data are dependent upon 'my' body (particularly those parts of it which are called 'sense-organs') induces us to form the concept of 'perception'. We do not find this concept in the language of unsophisticated, primitive people; they do not say, T perceive a tree', but simply, 'there is a tree'. 'Perception' implies the distinction between a subject which perceives and an object which is perceived. Originally the perceiver is the sense-organ or the body to which it belongs, but since the body itself — including the nervous system — is also one of the perceived things, the original view is soon 'corrected' by substituting for the perceiver a new subject, which is called 'ego' or 'mind' or 'consciousness'. It is usually thought of as somehow residing in the body, because the sense-organs are on the surface of the body. The mistake of locating consciousness or mind inside the body ('in the head'), which has been called "introjection" by R. Avenarius, is the main source of the difficulties of the so-called 'mind-
