variety of ideas: for in response to whatever it meets, the living and active Soul ideates, or gives rise to a representation. Thus, while the soul is one, its ideas or representations are many. Taken separately, they each express the psychic self-conservation. But brought in relation with each other, as so many acts or self-affirmations of the one soul, they behave as forces, and tend to thwart or check each other. It is as forces, as reciprocally arresting or fostering each other, that ideas are objects of science. When a representation is thus held in check, it is reduced to a mere endeavour or active tendency to represent. Thus there arises a distinction between representations proper, and those imperfect states or acts which are partly or wholly held in abeyance. But the latent phase of an idea is as essential to a thorough understanding of it as what appears. It is the great blunder of empirical psychology to ignore what is sunk below the surface of consciousness. And to Herbart consciousness is not the condition but rather the product of ideas, which are primarily forces. But representations are not merely in opposition,—impinging and resisting. The same reason which makes them resist, viz. that they are or would fain be acts of the one soul, but are more or less incompatible, leads them in other circumstances to form combinations with each other. These combinations are of two sorts. They are, first, complications, or “complexions”: a number of ideas combine by quasi-addition and juxtaposition to form a total. Second, there is fusion: ideas presenting certain degrees of contrast enter into a union where the parts are no longer separately perceptible. It is easy to see how the problems of psychology now assume the form of a statics and mechanics of the mind. Quantitative data are to be sought in the strength of each separate single idea, and the degree in which two or more ideas block each other: in the degree of combination between ideas, and the number of ideas in a combination: and in the terms of relation between the members of a series of ideas. A statical theory has to show the conditions required for what we may call the ideal state of equilibrium of the “idea-forces”: to determine, that is, the ultimate degree of obscuration suffered by any two ideas of different strength, and the conditions of their permanent combination or fusion. A mechanics of the mind will, on the contrary, deal with the rate at which these processes are brought about, the velocity with which in the movement of mind ideas are obscured or reawakened, &c.