George Berkeley's A Treatise Concerning the Principles of Human Knowledge explains the rationale behind his view that the very concept of a mind-independent object is necessarily incoherent. In this radical departure from John Locke's empiricism, Berkeley uses a host of arguments that nonetheless rest upon solidly Lockean ideas.
By mind, Berkeley means a thing “entirely distinct from” ideas “wherein they exist,” a non-physical receptacle containing thoughts. Berkeley reveals his Lockean empiricist underpinning in his understanding of the word object, or “things we perceive by sense,” To Berkeley, the term meaning through sight, touch, smell, palate, and hearing.mind-independent object refers to objects that exist “distinct from their being perceived.” and “strangely prevailing” The foundations of this sceptical argument break down into simple deductive logical form. Berkeley's first premise, that objects are what we perceive, is added to his second premise, that ideas are the only things we perceive. If we are to accept these premises, Berkeley's conclusion, that objects are ideas, is unavoidable. The idea of something that must be perceived by sense existing separately from its being perceived indeed seems indeed contradictory and incoherent, and it is thus not hard to see the cause of Berkeley's scepticism; he abhors this “repugnant” concept.
The conclusion derived from the implicit logic that follows seems airtight: objects are ideas, the concept of a mind-independent idea is unfathomable, and thus the concept of a mind-independent object is equally incoherent. However, Berkeley leaves us an avenue for escape. Although to accept this logic is to accept Berkeley deduction that objects are ideas, he does not prove that objects are ideas and only ideas; objects may possibly be perceived by sense and simultaneously exist in a mind-independent world. Berkeley represents this potentiality as “things like [ideas in the mind] whereof they are copies or resemblances, which things exist without the mind, in an unthinking substance.” However, Berkeley immediately attacks this avenue of thought with two related arguments.
In the first of these arguments, Berkeley's challenge, he attempts to show the reader that it is impossible to conceive of a mind-independent object. In daring the reader to conceive it possible for “a sound, or figure, or motion, or color, to exist without the mind, or unperceived,” Berkeley points out the obvious: no one can think of something that isn't being thought of. The equally obvious counter-argument, however, to posit that the readermight imagine something that could exist without being conceived of, does not undermine Berkeley's position. To think of such an object, Berkeley insists, requires the reader to “fram[e] in your mind certain ideas,”to conceive of the object in terms of the reader's own understanding. As an empiricist, Berkeley believes that this understanding is necessarily grounded in sense perception, and, thus, permits his reader no option but to think of the imagined object in such sense-based terms.
To support his challenge, Berkeley clarifies his position in Lockean terms with a second argument, attacking the distinction between the primary and secondary qualities of objects. Primary qualities, which materialists hold to “exist without the mind, in an unthinking substance which they call matter,” are, Berkeley asserts, no different from secondary qualities, which exist only in the mind. As Locke would view them, in an inert and senseless substance, primary qualities cannot exist. Berkeley believes it impossible to conceive, in his own mind at least, “any sensible thing or object distinct from the sensation or perception of it.” He opens the question to the reader as well, asking “anyone to reflect and try [to] conceive the extension and motion of a body [i.e. primary qualities], without all other sensible qualities,” implying that without using such other sensible qualities, the reader is left with no idea at all. Thus, when answering Berkeley's challenge, the readercannot use primary qualities alone, since, as Berkeley has established, these are indistinguishable from secondary qualities; the reader will always arrive at a description of an object in mind-related terms. Berkeley concludes, therefore, that mind-independent objects are in fact fundamentally incoherent, because they are simply indescribable without reference to ideas of mind-relation.
In a Lockean-empiricist framework, then, Berkeley is right that the idea of a mind-independent object is incoherent. However, when we consider the conclusions that Berkeley draws from this position, a powerful sceptical counter-argument arises that forces us to re-examine the basic empiricist assumptions on which Berkeley bases his argument. In his rejection of the coherence of a physical mind-independent world, Berkeley adopts a subjective idealist approach to explain human experience: in his view, all that exists are minds and ideas in the minds of subjects. He forcefully proposes that “there is not any other substance than spirit, or that which perceives.” That which a mind perceives is not, as Locke would posit, in any external world, but instead in “some other mind.”Those ideas that materialists would attribute to the external world are instead, Berkeley declares, “imprinted on the senses by the Author of Nature,” the mind of God.
