Leibnitz had not carried out the standpoint of idealism to its extreme. He had indeed, on the one side, explained space and motion and bodily things as phenomena which had their existence only in a confused representation, but on the other side, he had not wholly denied the existence of the bodily world, but had recognized as a reality lying at its basis, the world of monads. The phenomenal or bodily world had its fixed and substantial foundation in the monads. Thus Leibnitz, though an idealist, did not wholly break with realism. The ultimate consequence of a subjective idealism would have been to wholly deny the reality of the objective, sensible world, and explain corporeal objects as simply phenomena, as nothing but subjective notions without any objective reality as a basis. This consequence the idealistic counterpart to the ultimate realistic result of materialism—appears in George Berkeley, who was born in Ireland, 1684, made bishop of the Anglican Church in 1734, and died in 1753. Hence, though he followed the empiricism of Locke, and sustained no outward connection with Leibnitz, we must place him in immediate succession to the latter as the perfecter of a subjective idealism.

Our sensations, says Berkeley, are entirely subjective. We are wholly in error if we believe that we have a sensation of external objects or perceive them. That which we have and perceive is only our sensations. It is e. g. clear, that by the sense of sight we can see neither the distance, the size, nor the form of objects, but that we only conclude that these exist, because our experience has taught us that a certain sensation of sight is always attended by certain sensations of touch. That which we see is only colors, clearness, obscurity, &c., and it is therefore false to say that we see and feel the same thing. So also we never go out of ourselves for those sensations to which we ascribe most decidedly an objective character. The peculiar objects of our understanding are only our own affections; all ideas are hence only our own sensations. But just as there can be no sensations outside of the sensitive subject, so no idea can have existence outside of him who possesses it. The so-called objects exist only in our notion, and have a being only as they are perceived. It is the great error of most philosophers that they ascribe to corporeal objects a being outside the conceiving mind, and do not see that they are only mental. It is not possible that material things should produce any thing so wholly distinct from themselves as sensations and notions. There is no such thing as a material external world; mind alone exists as thinking being, whose nature consists in thinking and willing. But whence then arise all our sensations which come to us like the images of fancy, without our agency, and which are thus no products of our will? They arise from a spirit superior to ourselves—for only a spirit can produce within us notions—even from God. God gives us ideas; but as it would be contradictory to assert that a being could give what it does not possess, so ideas exist in God, and we derive them from him. These ideas in God may be called archetypes, and those in us ectypes.—In consequence of this view, says Berkeley, we do not deny an independent reality of things, we only deny that they can exist elsewhere than in an understanding. Instead therefore of speaking of a nature in which, e. g. the sun is the cause of warmth, &c., the accurate expression would be this: God announces to us through the sense of sight that we should soon perceive a sensation of warmth. Hence by nature we are only to understand the succession or the connection of ideas, and by natural laws the constant order in which they proceed, i. e. the laws of the association of ideas. This thorough-going subjective idealism, this complete denial of matter, Berkeley considered as the surest way to oppose materialism and atheism.