<p>Sigmund Freud, New Introductory Lectures on Psycho-Analysis (1933), reprinted in E. Kuykendall, Philosophy in the Age of Crisis, (New York: Harper & Row, 1970), p. 122. To philosophers the above sounds like the kind of move John Locke made when he posited the existence of material substance as an explanatory account for why collections of qualities regularly occur together. To the extent that the move is similar to Locke's, it is, of course, subject to the same types of criticisms.</p>