“These”, he writes, “are two very different things and carefully to be distinguished:  it being one thing to perceive and know the idea of white or black, and quite another to examine what kind of particles they must be, and how arranged ... to make any object appear white or black.”  “A man infallibly knows, as soon as ever he has them in his mind, that the ideas he calls white and round are the very ideas they are, and that they are not other ideas which he calls red or square....  This ... the mind ... always perceives at first sight; and if ever there happen any doubt about it, it will always be found to be about the names and not the ideas themselves.”

This sounds like high Platonic doctrine for a philosopher of the Left; but Locke’s utilitarian temper very soon reasserted itself in this subject.  Mathematical ideas were not only lucid but true:  and he demanded this truth, which he called “reality”, of all ideas worthy of consideration:  mere ideas would be worthless.  Very likely he forgot, in his philosophic puritanism, that fiction and music might have an intrinsic charm.  Where the frontier of human wisdom should be drawn in this direction was clearly indicated, in Locke’s day, by Spinoza, who says: 

“If, in keeping non-existent things present to the imagination, the mind were at the same time aware that those things did not exist, surely it would regard this gift of imagination as a virtue in its own constitution, not as a vice:  especially if such an imaginative faculty depended on nothing except the mind’s own nature:  that is to say, if this mental faculty of imagination were free”.

But Locke had not so firm a hold on truth that he could afford to play with fancy; and as he pushed forward the claims of human jurisdiction rather too far in physics, by assuming the current science to be literally true, so, in the realm of imagination, he retrenched somewhat illiberally our legitimate possessions.  Strange that as modern philosophy transfers the visible wealth of nature more and more to the mind, the mind should seem to lose courage and to become ashamed of its own fertility.  The hard-pressed natural man will not indulge his imagination unless it poses for truth; and being half aware of this imposition, he is more troubled at the thought of being deceived than at the fact of being mechanised or being bored:  and he would wish to escape imagination altogether.  A good God, he murmurs, could not have made us poets against our will.

Against his will, however, Locke was drawn to enlarge the subjective sphere.  The actual existence of mind was evident:  you had only to notice the fact that you were thinking.  Conscious mind, being thus known to exist directly and independently of the body, was a primary constituent of reality:  it was a fact on its own account.[6] Common sense seemed to testify to this, not only when confronted with the “I think, therefore I am” of Descartes,