The implications of Locke's dualism

"No one is more emphatic then Locke in opposing what is real to what we 'make for ourselves,' the work of nature to the work of mind. Simple ideas or sensations we certainly do not 'make for ourselves.' They therefore and the matter supposed to cause them are, according to Locke, real. But relations are neither simple ideas nor their material archetypes. They therefore, as Locke explicitly holds, fall under the head of the work of the mind, which is opposed to the real. But if we take him at his word and exclude from what we have considered real all qualities constituted by relation, we find that none are left. Without relation any simple idea would be undistinguished from other simple ideas, undetermined by its surroundings in the cosmos of experience. It would thus be unqualified itself, and consequently could afford no qualification of the material archetype, which yet according to Locke we only know through it or, if otherwise, as the subject of those 'primary qualities' which demonstrably consist in relations. In short, the admission of the antithesis between the real and the work of the mind, and the admission that relation is the work of the mind, put together, involve the conclusion that nothing is real of which anything can be said." -- T. H. Green, Prolegomena to Ethics, pp. 24-25