Anti-realism states that the existence of all objects depends upon human perception: ‘to be is to be perceived’. Idealism states that the immediate objects of perception are mind-dependent, what we today would refer to as sense data but Idealist George Berkeley referred to as ‘ideas.’ The theory suggests that perception is reality meaning that there is no external world to be perceived directly or indirectly.
The first evidence Berkeley used to back up his theory was his attack on John Locke’s theory of primary and secondary qualities. Indirect realism needs to make a distinction between primary qualities such as extension and position and secondary qualities like colour, taste or smell because there has to be some mind-independent primary qualities still attached to an unperceived object for it to continue to exist mind-independently in an external world. Berkeley claimed however that shape and size also depend on perception for example an object appears smaller when viewed from a greater distance. If there are no primary qualities then there can be no external world left. However, I don’t recognise this evidence as being of great significance as this was not what Berkeley believed to be his greatest argument. Berkeley’s strongest argument in support of his idealism was The Master Argument: you cannot conceive of an external world so how can you assume it exists. He used the example of trying to conceive of an unperceived tree but you cannot because through the act of picturing the tree you perceive the tree. However, this argument does not stand as there is an important distinction to be made between the thought of the tree and the tree itself and you only perceive the thought of the tree.
So far I have argued that there are no significantly convincing arguments to