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INSTITUTES OF METAPHYSIC.
PROP. XVII.————
to clear up a very obscure topic in ancient philosophy, and one on which no light is thrown in any history of speculation—the question, namely, What did Plato and his predecessors understand by the substantial in existence? They understood by this expression whatever could exist without anything else necessarily existing along with it. What can only so exist is a point which can be properly enucleated only in the ontology.
Two main ambiguities in the old systems.18. The ambiguities of language which pervade the old philosophies, and have thus prevented their truth from being appreciated or understood, are mainly these two: First, The term τὸ ὄν (true Being) is used both in an epistemological and in an ontological acceptation; this is to say, it is employed to designate both the substantial in cognition and the substantial in existence. This twofold use of the term would have been quite legitimate, had any critical argumentation been employed to prove the coincidence of the known substantial and the existing substantial; but no such reasoning having been resorted to, this double signification could not but be perplexing. In the same way) the term γιγνόμενον is also used indiscriminately to signify both the phenomenal in existence and the phenomenal in cognition, the proper term for the latter being the sensible (τὸ αἰσθητόν). Secondly, A still more serious ambiguity was this: The term