How men's words fail when they stand for Substances.
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“He that applies his names to ideas different from their common use, wants propriety in his language, and speaks gibberish. And he that hath the ideas of substances disagreeing with the real existence of things, so far wants the materials of true knowledge in his understanding, and hath instead thereof chimeras. 32. How men's words fail when they stand for Substances. In our notions concerning Substances, we are liable to all the former inconveniences: v. g. he that uses the word TARANTULA, without having any imagination or idea of what it stands for, pronounces a good word;” source