[AC] The assumption that these two expressions are or ought to be synonymous is tacitly made by Mr. Mill at the opening of this chapter. He opens it with a passage from the _Discussions_, in which Hamilton says that the existence of _things in themselves_ is only indirectly revealed to us "through certain qualities _related to our faculties of knowledge_;" and then proceeds to show that the author did not hold the doctrine which these phrases "seem to convey in the only substantial meaning capable of being attached to them;" namely, "that we know nothing of _objects_ except their existence, and the impressions produced by them upon the human mind." Having thus quietly assumed that "things in themselves" are identical with "objects," and "relations" with "impressions on the human mind," Mr. Mill bases his whole criticism on this tacit _petitio principii_. He is not aware that though Reid sometimes uses the term _relative_ in this inaccurate sense, Hamilton expressly points out the inaccuracy and explains the proper sense.--(See _Reid's Works_, pp. 313, 322.) The most curious circumstance about this criticism is, that, if not directly borrowed from, it has at least been carefully anticipated by, Hamilton himself. Of the distinction between primary and secondary qualities, as acknowledged by Descartes and Locke, whose theory of external perception is identical with that which Mr. Mill would force on Hamilton himself, Hamilton says: "On the general doctrine, however, of these philosophers, both classes of qualities, as known, are confessedly only states of our own minds; and while we have no right from a subjective affection to infer the existence, far less the corresponding character of the existence, of any objective reality, it is evident that their doctrine, if fairly evolved, would result in a dogmatic or in a sceptical negation of the primary no less than of the secondary qualities of body, as more than appearances in and for us."[AD] It is astonishing that Mr. Mill, who pounces eagerly on every imaginable instance of Hamilton's inconsistency, should have neglected to notice this, which, if his criticism be true, is the most glaring inconsistency of all. [AD] _Reid's Works_, p. 840.