Berkeley's aim in the first dialogue is to prove that materialism is false—that is, that we have no reason to believe in the existence of mind-independent material objects. With this end in mind, he launches a two-staged attack against the thesis. He attempts to prove first that we have no immediate perception of mind- independent material objects, and then that we have no basis on which to infer the existence of mind- independent material objects from our immediate experience. Since Berkeley is an empiricist, establishing that we do not obtain evidence for the existence of mind-independent material objects in either of these two ways, amounts in his eyes to proving that we do not obtain evidence for mind-independent material objects, period. For an empiricist, all knowledge must either come directly through sensory experience or else be inferred based on such experience.

To prove that everything we perceive in our immediate experience is mind-dependent, Berkeley presents us with two arguments. Grounding both arguments is the seemingly unobjectionable claim that what we immediately perceive of the world is sensible qualities (such as color, taste, smell, heat, shape, size, and so on). In the first of these arguments, he tries to get us to admit that our experience of the world (at least our experience of color, taste, sound, heat, and smell, as opposed to size, shape, and motion) fundamentally involves pleasure and pain, and that these sensations cannot exist in material objects.

By hooking up all of our sensations of secondary qualities with pleasure and pain, then, he forces us to admit that none of these sensible qualities can exist outside of mind. Berkeley uses the following line of reasoning. Imagine that you are experiencing intense heat, he instructs us. How do you experience this? As pain, naturally. But can pain exist in an insentient object? Of course not. So, pain cannot be in material objects; pain can only be in a mind. But if we feel intense heat as pain, that means that intense heat also cannot exist outside of mind. So intense heat is mind dependent. This means that all heat must be mind-dependent since intense heat is obviously the same kind of thing as all other degrees of heat.

The argument from pleasure and pain only applies to secondary qualities, but Berkeley must also prove that primary qualities are mind dependent if he is to prove that everything we receive through immediate experience is mind dependent. His second argument, therefore, applies to primary qualities as well. Here Berkeley points to instances of perceptual relativity, such as the fact that colors can look different in varied lighting conditions or that a piece of wheat can be big to a mite and small to a human.

Given that we have these highly variable experiences of both primary and secondary qualities, Berkeley concludes that what we are experiencing cannot be anything mind-independent. After all, material objects are supposed to be stable things, and if they are not changing constantly, then they cannot be what we are experiencing as changing so frequently. With these two arguments, Berkeley feels he has shown that everything we immediately perceive (i.e. all sensible qualities) is mind-dependent. In other words, he thinks he has shown that we get no evidence of mind-independent material objects from our immediate experience.

If we do have any evidence for the existence of mind-independent material objects then, this must come from some sort of inference that we make based on our immediate experience. Berkeley's next task, therefore, is to show that no such inference is warranted. He shows, first, that we cannot infer the existence of matter as some sort of support for sensible qualities (i.e. as a substratum), because this notion is incoherent; next he shows that the idea of material objects as the archetypes for our ideas is equally incoherent. He does the same for the thesis that material objects are the cause of our ideas. Since he believes that these are the only three inferences one might make, once he has shown that these are unwarranted, he believes that he has conclusively shown that we have no evidence at all for the existence of mind-independent material objects.

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