Berkeley claims that his ontology is a validation of common sense. The common sense view that he believes he is defending consists of four interrelated ontological and epistemological claims:

(1) We can trust our senses;
(2) The things we see and feel are real; 
(3) The qualities we perceive as existing really do exist;
(4) All skeptical doubt about the real existence of things is, therefore, precluded.

The philosophical view Berkeley opposes—espoused by John Locke and René Descartes in particular—distinguishes between subjective ideas, which exist only as the content of our consciousness, and real material things, which exist objectively in the external world and do not depend on their being apprehended by any mind to exist. In this view, it is only the ideas and not the “real things,” of which the ideas are representations, to which we have immediate access (counter to Berkeley’s claim two). Therefore, this view raises the worry of how we can know anything about the external world (counter to Berkeley’s claim four). The philosophical view also draws a distinction between primary qualities (such as size, motion, and shape) and secondary qualities (such as color, sound, taste, and smell). According to the philosophers, primary qualities really exist within the objects of perception, but secondary qualities are nothing more than ideas (counter to Berkeley’s claims one and three).

According to Berkeley's ontology, there are only two types of things existing in the world: ideas and the spirits which have them. He identifies sensible objects such as flowers, chairs, and hands, with those ideas we call "sensations". In other words, he eliminates the philosopher's distinction between the subjective impressions of sense objects and the "real existence" of those objects. The real existence of sensible objects, Berkeley claims, is just their existence as immediate objects of perception. Berkeley's identification of sensible objects with sensory impressions does seem to render trivially true those claims he regards as comprising common sense. We cannot possibly doubt the existence of something we see or touch, since its being seen or touched just is that thing's existence. There is no question, then, of whether we can trust our senses, whether the things we see and feel are real, or whether the qualities we perceive as existing really do exist. There can be no skeptical worry that we do not know the real existence of things with certainty.

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