Extension, Existence, Actuality

While the existence, proposed by Spinoza in II, viii of the Ethics, of "ideas of particular things, or modes, that do not exist", seems to contradict the Idea-Thing correspondence proposed in the previous proposition, he argues that, to the contrary, it is "evident" from the latter.  Now, the example--'non-existing' rectangles--that he presents in the included Note may be more illuminating than he seems to be appreciate.  For, what he seems to mean by 'non-existent', is 'non-actual', i. e. nevertheless both existing and possessing extension.  In other words, in his system, all the modifications of the Deity's attribute of Thought both exist and are ideas of an extended entity, though not all of them are actualized, a distinction more recently classified by a term to which Spinoza has precluded use, namely 'modal'.  The Theological significance of that distinction emerges later, since it grounds the apparent separation of Mind and Body, proposed in V, xxiii, which, rather than amounting to a reversion to the traditional Supernaturalism that his system challenges, is, more precisely, the separation of a possible Mode from an actual one.