PROP. XVI.————
necessity, known along with it. And this something, whatever it may turn out to be, is known substance, according to the definition. Therefore there is a substantial in cognition; in other words, substance is knowable, and is known by us.
OBSERVATIONS AND EXPLANATIONS.
This proposition proves nothing as to existing substance.1. The words "known" and "in cognition" are here inserted (as on other occasions) in order to guard against the supposition that this definition fixes anything, or that this proposition proves anything, in regard to existing substance. Known substance may subsequently turn out to be coincident with existing substance; but this is not to be assumed, and it is not assumed at this place. All that is defined is known substance, and all that is proved is that there is a known substance, not that known substance is existing substance.
Neither does it declare the nature of known substance.2. The reader is also requested to bear in mind that this proposition says nothing as to what known substance is; it merely states and proves that there is such a thing. What the thing is—in other words, what corresponds to the definition—is declared in the next proposition. This remark is made lest any perplexity or dissatisfaction should be occasioned by the vagueness which necessarily hangs over a statement which merely announces that a certain thing