 The second conviction, also meant to be damaging to Locke’s view about substances, on which Berkeley rests his case in favor of idealism is the more strictly metaphysical claim (2) that “an idea can be like nothing but an idea” (1710: Part I, §8). Although this claim is initially put forward in the context of his well-known criticism of Locke’s primary-secondary-quality distinction, it is equally relevant for his denial that there are things “without the mind”. The reasoning on which this claim is based seems to be the following: For two items to stand in the relation of likeness they must have something in common. However, if an idea is mind-dependent and if ideas are all there is for the mind, then what is “without the mind” must be different in every respect from an idea. Thus a relation of likeness cannot obtain between ideas “in the mind” and things “without the mind”. Berkeley puts this point quite bluntly by appealing to observation: