  Berkeley’s ontology is not exhausted by the ideal, however. In addition to perceived things (ideas), he posits perceivers, i.e., minds or spirits, as he often terms them. Spirits, he emphasizes, are totally different in kind from ideas, for they are active where ideas are passive. This suggests that Berkeley has replaced one kind of dualism, of mind and matter, with another kind of dualism, of mind and idea. There is something to this point, given Berkeley’s refusal to elaborate upon the relation between active minds and passive ideas. At Principles 49, he famously dismisses quibbling about how ideas inhere in the mind (are minds colored and extended when such sensible qualities “exist in” them?) with the declaration that “those qualities are in the mind only as they are perceived by it, that is, not by way of mode or attribute, but only by way of idea”. Berkeley’s dualism, however, is a dualism within the realm of the mind-dependent.