Here, then, are our data. The theory of Monism teaches that what we perceive as matter in motion, _x_, is the obverse of what we know as mind, _z_. What, then, do we know of _z_? In the first place, we well know that this is the only entity with which we are acquainted, so to speak, at first hand; all our knowledge of _x_ (which is the only other knowledge we possess) is possible only in so far as we are able to translate it into terms of _z_. In the next place, we know that _z_ is itself an entity of the most enormous complexity. Standing as a symbol of the whole range of individual subjectivity, it may be said to constitute for each individual the symbol of his own personality--or the sum total of his conscious life. Now each individual knows by direct knowledge that his conscious life is, as I have said, of enormous complexity, and that numberless ingredients of feeling, thought, and volition are therein combined in numberless ways. Therefore the symbol _z_ may be considered as the sum of innumerable constituent parts, grouped _inter se_ in numberless systems of more or less complexity. From these considerations we arrive at the following conclusions. The theory of Monism teaches that all _z_ is _x_; but it does not, therefore, necessarily teach that all _x_ is _z_. Nevertheless, it does teach that if all _x_ is not _z_, this must be because _x_ is _z_, _plus_ something more than _z_, as a little thought will be sufficient to show. Thus, the four annexed diagrams exhaust the logical possibilities of any case, where the question is as to the inclusion or exclusion of one quantity by another. In Fig. 1 the two quantities are coincident; in Fig 2 the one is wholly included by the other; in Fig. 3 it is partially included; and in Fig. 4 wholly excluded. Now in the present case, and upon the data supplied, the logical possibilities are exhausted by Figs. 1 and 2. For, upon these data, Figs. 3 and 4 obviously represent logical impossibilities; no part of Mind can, according to these data, stand outside the limits of Matter and Motion. Therefore, if the Ego is not coincident with the Non-ego (or if all _x_ is not _z_, as in Fig. 1), this can only be because the Ego is less extensive than the Non-ego (or because _x_ is _z plus_ something more than _z_, as in Fig. 2). [Illustration: Fig. 1] [Illustration: Fig. 2] [Illustration: Fig. 3] [Illustration: Fig. 4] Of these two logical possibilities Idealism, in its most extreme form, may adopt the first. For Idealism in this form may hold that apart from the Ego there is no external world; that outside of _z_ there is no _x_; that the only _esse_ is the _percipi_. But, as very few persons nowadays are prepared to go the length of seriously maintaining that in actual fact there is no external world save in so far as this is perceived by the individual mind, I need not wait to consider this possibility. We are thus practically shut up to a consideration of the possibility marked 2.