Locke used his own principles only in ways consistent with common sense; Berkeley and Hume both pushed them to paradoxical conclusions. The philosophy of Berkeley, to my mind, has not received quite the attention and respect that it deserves--not that I agree with it, but that I think it ingenious and harder to refute than is often supposed. Berkeley, as everyone knows, denied the reality of matter, and maintained that everything is mental. In the former respect I agree with him, though not for his reasons; in the latter respect, I think his argument unsound and his conclusion improbable, though not certainly false. However, I will leave the development of my own views to a later chapter, and confine myself to Berkeley’s argument. Berkeley contended that when, for example, you “see a tree”, all that you really _know_ to be happening is in you, and is mental. The colour that you see, as Locke had already argued, does not belong to the physical world, but is an effect upon you, produced, according to Locke, by a physical stimulus. Locke held that the purely spatial properties of perceived objects really belong to the objects, whereas such things as colour, softness, sound, etc., are effects in us. Berkeley went further, and argued that the spatial properties of perceived objects are no exception. Thus the object perceived is composed entirely of “mental” constituents, and there is no reason to believe in the existence of anything not mental. He did not wish to admit that a tree ceases to exist when we do not look at it, so he maintained that it acquires permanence through being an idea in the mind of God. It is still only an “idea”, but not one whose existence depends upon the accidents of our perceptions. The real objection to Berkeley’s view is rather physical than metaphysical. Light and sound take time to travel from their sources to the percipient, and one must suppose that something is happening along the route by which they travel. What is happening along the route is presumably not “mental”, for, as we have seen, “mental” events are those that have peculiar mnemic effects which are connected with living tissue. Therefore, although Berkeley is right in saying that the events we know immediately are mental, it is highly probable that he is wrong as to the events which we infer in places where there are no living bodies. In saying this, however, we are anticipating the results of a fuller discussion in a later chapter.