In the Essay Berkeley has two principal aims. The first is negative. Raising the question how and why we make by vision — as on the whole we make pretty successfully — our everyday judgements of the sizes, distances, and positions of objects, Berkeley first contends — contrary to much current theorizing of his day — that such judgements are not made on the basis of a knowledge of optics. It may for example be true that, as an object recedes from us, the angle at which the optic axes converge upon it decreases; but since we do not see those axes or the angle at which they converge, that cannot explain why we judge the object to be receding. His point here, surely a correct one, is that the everyday visual judgements we all make of distance and size must be in some way based on how things look to us, not on theorems of optics which, however sound in their own sphere, cannot constitute direct visual evidence and for that matter are often totally unknown to persons of perfectly sound visual competence.
Berkeley then turns to the question of how it comes about that 'how things look' does enable us to make, on the whole, reliable judgements as to how things are. And here he offers the double contention that the connection between visual 'clues' and actual states of affairs; first is learned only by experience, not calculable a priori, and second, is completely contingent, and indeed arbitrary. In support of this contention he argues that objects are, strictly speaking, tangible objects only; they are not, strictly, literally seen — or, for that matter, heard. The 'proper objects' of hearing are sounds, and only indirectly or by inference the things that make sounds. Similarly, he holds, there are purely visual 'proper objects' of vision; and we learn only by experience to make inferences from these 'proper objects' to states of (tangible) things. States of things are, as we learn by experience, fairly reliably correlated with the occurrence of distinctive purely visual objects, but these correlations, however reliable, are fundamentally quite arbitrary — like, for instance, the link between the word 'red' and the colour red. God maintains these correlations for the benefit of his creatures, so that the objects of vision can be said to constitute a 'divine visual language' by which, once we have learned it, we are 'told' about the tangible things in our environment.
Readers of the Essay must have been struck, even in 1709, by one conspicuous omission from it. John Locke's many admirers, for example, would have agreed with Berkeley that the direct objects of vision were purely visual 'ideas', and that these were properly quite distinct from what they would have called 'external bodies'. But why say that the connection between visual ideas and states of things is arbitrary, maintained purely at God's pleasure? For surely it is causal. Was there not a well-established, or at any rate widely accepted, theory as to the causation of perception, according to which visual ideas, and for that matter all 'ideas of sensation', were the causal products of states of things and of their action upon our sense organs? Why is this theory, which at least appears to offer a unified, non-arbitrary explanation of the connections between our ideas of sensation, not even mentioned by Berkeley?
Berkeley's total rejection of that theory — Locke's so-called 'causal' or 'representational' theory of perception — is made clear in the Principles. The theory was that the universe is, fundamentally, a system of solid bodies in mechanical interaction; that the objects of everyday experience are themselves systems of 'corpuscles', 'insensible particles', in mechanical interaction; and that, in perception, these bodies act mechanically upon our various sense organs, causing ultimately, by way of causal chains in the nervous system and brain, 'ideas of sensation' to occur 'in the mind'. Such ideas are the 'immediate objects' of perception, and inform us — or, so Locke held, in some cases misinform us — as to the existence and character of the 'external' bodies that are their originating causes.
Berkeley's chief grounds for rejecting this theory were these. First, he took it to be self-defeating — if true, it could not be known to be true. For if the contents, the 'immediate objects', of perception are all, and only, ideas, what ground could there be in perception for supposing the existence of anything else? Second, and for much the same reason, he regarded the theory as ontologically redundant. Given observers ('spirits') and the ideas that they have, which actually constitute their experience, why add a supposedly distinct 'external' world which forms no actual part of anyone's experience at all? Experience would be just the same if no such world existed: why, then, suppose that it does exist? Now the answer to that question was supposed to be that the existence of 'external bodies' causes and therefore explains the occurrence of ideas in our experience; but Berkeley's third contention is that that cannot be so. For, he asserts, only an active, animate being can be a cause; the only true case of causation is volition, intelligent agency, so that the mere mechanical happenings postulated in Locke's theory could in principle neither cause nor explain anything.
Berkeley's own views in the Principles could be said to take the form of a generalization, to all sensory modes, of the account of vision put forward in his Essay. He had held there that the 'proper objects' of vision are purely visual ideas 'in the mind', generated by the direct action of God so as to 'tell' us about tangible objects 'in circumambient space'. In the Principles he dispenses with those objects. Every sense, he now holds, even the sense of touch, has its own 'proper objects', all 'ideas', all 'in the mind'; there are (besides minds or 'spirits') only ideas; and God's work is now said to be, not merely that of informing his creatures by 'visual language' of independent things, but of so maintaining the complex correlations between all ideas, of all the senses, as to sustain in the experience of us all the apparent unity, continuity, and coherence of a common world. He claims for this extraordinary doctrine, first — surprisingly enough — that it accords with common sense. Locke, with his 'scientific' theory, had been obliged to shock us by concluding that the world is in many ways not as it appears; Berkeley holds that, on his view, the world is exactly as it appears — for, in fact, it is 'what appears', no more and no less. Then his doctrine is also, he claims, ontologically economical, non-redundant: to describe our experience we need nothing more than 'spirits' and 'ideas'; and Berkeley makes no further, gratuitous existential assumptions. Then, since the cause of ideas, in Berkeley's doctrine, is the will of God, he has, he claims, a real cause, a truly explanatory agency — and, last but for Berkeley not least, one that firmly entrenches theism in the nature of things, as the ground of all being.
What then of the 'scientific' theory of perception, according to which 'particles' acted on sense organs to cause sensation? Berkeley was at first inclined to dismiss all such talk as mere rubbish, to be simply abandoned. But later he contrived to accommodate this theory also, as not a genuinely causal theory, not really explanatory, and indeed not true, but a possibly useful purely theoretical construct to assist us in predicting how the true cause — God's will — was likely to operate in our experience. This was, indeed, his general account of all scientific theories that postulated entities not accessible to direct observation.
(Published 1987)
— Sir Geoffrey Warnock
