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  where he disagreed with Locke’s rejection of innate ideas. Leibniz writes that there is no way all our ideas could come from experience since there are no real causal interactions between substances. In addition, Locke’s claim that the mind was a blank paper at birth violated Leibniz’s Principle of the Identity of Indiscernibles.[[CiteRef::Cook (2013)]] Fellow empiricist George Berkeley was also critical of Locke’s distinction between primary and secondary qualities—Berkeley claimed that primary qualities as well as secondary qualities were a product of the human mind, and not a part of the object.[[CiteRef::Berkeley (1957)]]