Note 9 — ÉTUDE SUR STUART MILL

The definition above given of a triangle, obviously comprises not one, but two propositions, perfectly distinguishable. The one is, "There may exist a figure bounded by three straight lines;" the other, "And this figure may be termed a triangle". The former of these propositions is not a definition at all; the latter is a mere nominal defition, or explanation of the use and application of a term. The first is susceptible of truth or falsehood, and may therefore be made the foundation of a train of reasoning. The latter can neither be true nor false; the only character it is susceptible of is that of conformity to the ordinary usage of language.