– Idealism is broadly the thesis that reality is mental – more specifically, reality is constituted by perception (Berkely), and the only things known are what is given in conscious experience.
– An argument for this view could be sketched out as follows: everything we know about reality is based on our own experience, all our experience is mental in nature (given in consciousness and mediated by the mind) therefore, reality is ultimately mental. All we experience or perceive are ideas (or sense-data, to use a more modern term) and bundles of ideas.
– As is commonly noted, this is an extreme form of empiricism.
– A simple objection: from the fact that all we perceive is X (in this case, ideas) it does not follow that all is X (granting for the sake of argument the Way of Ideas). That leap is quite unjustified in this case.
– John Haldane notes another objection:
‘Berkeley maintained that the realist assumption that some things are mind-independent is self-contradictory, since just as an object cannot be both seen and unseen, so nothing can be both conceived and unconceived. There is a difference, however, between the fact of conceiving of something and the content of what is conceived; and it is not contradictory to conceive of something as existing unconceived. Although I may be conceiving it, it is not thereby part of an object’s nature, let along of its being, to be conceived of by me or by anyone else.’
– Issue could also be taken with the empiricist epistemology that undergirds Berkeley’s project, and, for that matter, the Way of Ideas as a whole (the latter could be criticized just by pointing out how many skeptical problems arise when such an idea is entertained).