Berkeley argues for idealism by appealing to cases that seem to demonstrate that everything is mind- dependent. First, Berkeley states that sensible things are immediately perceived by sense. Secondly, he states that senseless material substances cannot perceive or be perceived apart from a mind. For instance fire cannot perceive or be perceived as heat apart from the mind. Sugar cannot perceive or be perceived as sweet apart from the mind. Something is not painful unless there is a mind to perceive it. The same goes for pleasure, heat, cold, and sound. Berkeley uses pain, pleasure, heat, cold, sound, colors as case examples to show that apart from the mind one cannot perceive them. In other words, their existence is dependent upon the mind. This leads Berkeley to say that the sensation of matter is also dependent upon the mind. Hence, matter does not exist apart from the mind. However, only ideas are dependent upon the mind. Therefore, the only things that can exist are ideas.
I think the argument for idealism can be stated as follows:
1. Sensible things can only be perceived by the mind.
2. Matter is a sensible thing perceived.
3. Therefore, matter can only be perceived by the mind.
4. Things that can only be perceived by the mind are mind-dependent.
5. Matter can only be perceived by the mind.
6. So, matter is mind-dependent.
7. Things that are mind-dependent cannot exist apart from the mind.
8. Matter is mind-dependent.
9. Hence, matter cannot exist apart from the mind.
The argument seems strait forward, but premise (7) is objected to by Hylas in Berkeley’s dialogues. But the brilliance of this argument is that if the former premises are granted it follows that one ought to accept premise (7).