As it is a serious matter, however, to accept a view of the real which such a thinker as Locke could not reconcile with the reality of relations, and which logically implies that knowledge is not of the real; and as on the other hand there is something in the opposition between the real and the work of the mind which seems to satisfy an imperative demand of common-sense; it becomes important to enquire whether we interpret that demand aright. Is there not a conception of the real behind the opposition in question, which seems to require us to accept it, but which in truth we misinterpret in doing so? (§ 21 ¶ 1)

We constantly find Locke falling back on the consideration that of simple ideas we cannot make one to ourselves. They force themselves upon us whether we will or no. It is this which entitles them in his eyes to be accounted real. The work of the mind, on the other hand, he considers arbitrary. A man has but to think, and he can make ideas of relation for himself as he pleases. Locke thus indicates what we may call the operative conception—operative as governing the action of our intelligence—which underlies the opposition between the real and the work of the mind. This is the conception which we have described already as that of a single and unalterable system of relations. It is not the work of the mind, as such, that we instinctively oppose to the real, but the work of the mind as assumed to be arbitrary and irregularly changeable. (§ 21 ¶ 2)