  A further difficulty for the tenability of the Ideas in Schopenhauer’s system is the fact that he often refers to Ideas in the plural. For Schopenhauer, space and time are the principium individuationis; but since the Ideas are independent of space and time, it is not clear how they can be individuated at all. One option for understanding the place of the Ideas in his system would be to see them as playing the role of an epistemic rather than metaphysical bridge between the one will and the many phenomena. This helps to explain their individuated status as follows: In a suggestive metaphor, Schopenhauer likens the Ideas to “steps on the ladder of the objectivation of that one will, of the true thing in itself” (WWR I, 198); if one understands the “ladder”—the ensemble of Ideas—as part of the world as representation, then each Idea—each “step” on the ladder—is a universal perceived in various particular spatiotemporal objects. The Ideas then are the essential features of objects or states of affairs that human beings may perceive when their attention is focussed squarely on the ‘what’ rather than on the ‘why’ or ‘wherefore’ of phenomena. It should be noted, however, that the Ideas are not abstracted by the subject as are concepts on Schopenhauer’s view, but are, rather, perceived directly in them.  In sum, the Ideas seem to make the most sense within his system as “abstract objects”—objects that are not spatiotemporal, which do not stand in causal relationship with anything, and which have not been abstracted like a concept, but rather, are the real, objective, essential aspects of the world as representation as perceived by a will-less subject (WWR I, 234, 236). The crucial role that they play in Schopenhauer’s system is that they are the objects of all aesthetic experience—both of the artist and spectator—and their perception constitutes insight into the essential nature of the phenomenal world.