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12 common with many other inquiries, with every inquiry, I mean, instituted for ascertaining the essence and the thing itself, it might hastily be supposed that, as demonstration is the method for studying particular bodies in their accidents, there may be some one special method of investigation when our object is to learn what is the essence of a thing, and that that method ought to be sought for on this occasion. If, however, there is no one common method for ascertaining what any thing in itself is, the systematic treatment of our subject is rendered still more difficult; for, in that case, it will be necessary to adopt, for each particular subject, some one particular method. Although it may be manifest, besides, that the inquiry should be by some kind of demonstration, or division, or other method, there will still remain many difficulties and many liabilities to error in fixing upon the principles from which the inquiry should set out; for the principles of different subjects differ, as those of number are not those of plane surfaces.

It may be well, perhaps, before proceeding further, to distinguish the “genus” to which Vital Principle belongs, and determine what it is—determine, I mean, whether it is a something and essence, or quantity, or quality, or any other of the classified categories; as also, a distinction of no small importance, whether it is among entities in potentiality, or whether rather it is a reality. We have to consider too whether