 To fend off this objection Spinoza must find a way of explaining the possibility of representing something (such as a winged horse) without committing to its existence, while drawing solely on the resources of particular, intrinsically affirmative ideas. His proposal focuses on countervailing ideas: ideas that affirm or posit something that negates or “excludes [tollere]” the existence of an object represented by other ideas. For example, a child “imagining a winged horse, and not perceiving anything else…that excludes the existence of the horse….will necessarily regard the horse as present” (E2p49s [III.B.(ii)]; G/II/134). But, with some schooling, the child’s original idea of a winged horse can be offset by another idea (say, by the rational representation of equine bones as, in general, too heavy to be lifted by feathers). Spinoza’s proposal explains not only how the ordinary experience of mere entertainment of ideas is possible, but, more significantly, it arguably offers a genealogy of negation as a basic mental operation derived from affirmation (cf. Donagan 1988:46).