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 sciences; and it bears the same relation to them that mechanics does to the physical.

All this is doubtless true; and yet a very great difficulty has been experienced in condensing into a clear definition the essence of psychology. This is proved by the multiplicity of definitions attempted. They are so many because none of them has proved completely satisfactory. Their abundance shows their insufficiency. I will try to introduce a little order into these attempts, and propose to distribute the definitions of psychology into the following categories:—


 * 1. The definition by substance; the metaphysical definition par excellence.


 * 2. The definition by enumeration.


 * 3. The definition by method.


 * 4. The definition by degree of certainty.


 * 5. The definition by content.


 * 6. The definition by point of view.


 * 7. The definition by the peculiar nature of mental laws.

We will rapidly run through this series of efforts at definition, and shall criticise and reject nearly the whole of them; for the last alone seems exact—that is to say, in harmony with the ideas laid down above.

Metaphysical definition has to-day taken a slightly archaistic turn. Psychology used to be