George Berkeley: Three Dialogues Between Hylas and Philonous

Berkeley’s attack on Locke’s indirect realism: we cannot know the nature of mind-independent objects

Berkeley argues that Locke’s notion of substance could not cause ideas since they are too different. Perceptions are ‘fleeting and variable’ yet according to Locke, substance must be unchanging and fixed. One can also ask (though not Berkeley’s example): how can something invisible like a photon cause something visible, like light?

If Locke’s representational causal theory of perception were true, it could never be known to be true – since one cannot correlate impressions or ideas with the qualities of which they are impressions or ideas in order to give inductive confirmation to the postulated causal connection.

If it is a hypothesis – an inference to the best explanation – then it is not a hypothesis that can ever be confirmed or disconfirmed in experience. (E.g. The existence of Uranus was hypothesised because of the movements of the other visible planets, but even at the time it was [at least in principle] possible to confirm this hypothesis.)

Berkeley’s attack on the primary/secondary distinction

Berkeley argued that the Locke’s primary/secondary distinction was false. He argued that primary qualities are mind-dependent because they are subject to  interpersonal and intrapersonal perceptual variation (objects can appear to have different sizes, shapes, speeds, etc) just like secondary qualities (eg objects can appear to have different colours, tastes, etc) and are therefore mind-dependent.

He also argued that we cannot imagine primary qualities without secondary ones. E.g. You cannot imagine a colourless, tasteless apple. You end up stripping away the apple itself.