Briefly explain Berkeley's idealism.

For Berkely, there is not a world with physical objects that is external to us. The sense data we perceive with our sense organs are bundled together as 'ideas'. For example the idea 'chair' is a bundle of sense data such as browness, rods and plank shapes etc. Unlike indirect realists, Berkeley does not think these ideas represent anything outside of our perception; objects only exist when someone is perceiving.