The real essence of that or any other sort of substances, it is evident, we know not; and therefore are so undetermined in our nominal essences, which we make ourselves, that, if several men were to be asked concerning some oddly-shaped fœtus, as soon as born, whether it were a man or no, it is past doubt one should meet with different answers.
1959 , John Locke, chapter 6, in An Essay Concerning Human Understanding, vol. 2, New York, N.Y.: Dover Publications, Inc., page 77