Abstract: Berkeley attacked Locke's theory of abstract ideas, partly sound though partly unfair. He held, apparently wrongly, that the issue over abstract ideas generates the other philosophical issues between himself and Locke. He used Locke's supposed view about secondary qualities against him in the debate over immaterialism, but his way of doing so depended on attributing to Locke the textually least visible and philosophically worst of his views on this topic, namely, that secondary qualities are in the mind. On the topic of substance as substratum, Berkeley utterly conflates two distinct issues: substratum that supports qualities, and matter that causes ideas.

Keywords: abstract idea, Berkeley, idea, immaterialism, Locke, quality, secondary qualities, substance,