Berkeley’s criticism of Locke’s theory concerning substances is not carried out for its own sake. On the contrary, it is meant to establish what Berkeley thinks to be the unavoidable metaphysical consequences of a position that takes ideas “in the mind” to be the only material for the operations of the mind in its acquisition of knowledge. These metaphysical consequences consist in a thoroughgoing idealism or “immaterialism” with respect to the nature and constitution of things or substances. Be