I now pass from the attitude of expositor to the attitude of critic. And first I will attack a quite outstanding position, namely Dr. Stoney’s assumption that Clifford’s hypothesis which he supports and extends is _the_ monistic hypothesis, and by implication that it is the _only_ monistic hypothesis. In opposition to this I venture to affirm that there are several forms or phases of monism. I have not space to discuss the matter; and must content myself with a bare enumeration of some of the logically possible forms of Dualism and of Monism. 1) DUALISM. _A._ _Synthetic Dualism_: according to which there are two entities, the mind and the body; and these _a_) either work side by side, without interaction, in pre-established harmony (_philosophic dualism_), _b_) or interact the one on the other (_empirical dualism_). _B._ _Analytic Dualism_: according to which there are two elements as the result of analysis; _motion_ (with or without a material basis) and _consciousness_; the two elements being related in such a way that consciousness is inseparably associated with certain complex modes of motion. 2) MONISM. _A._ _Synthetic monism_: according to which there is but one entity. And this entity may be: _a_) The body, of which consciousness is a product (_materialistic or physical monism_); _b_) The mind, of which the body in common with the world of phenomena is a fiction (_idealistic monism_); _c_) The conscious organism, exhibiting certain transformations of energy which are felt as psychical states (_scientific monism_). _B._ _Analytic monism_: according to which analysis discloses but one element; and this may be _a_) _motion_, of which (or of one phase of which) consciousness is merely the psychical aspect (_analytic materialism_); _b_) _consciousness_, of which motion is merely the phenomenal aspect (_analytic psychism_); _c_) _x_ (_the unknowable_) of which motion is the physical aspect and consciousness the psychical aspect (_monistic agnosticism_).