  The spatio-temporal, material character of particulars also contributes directly to the explanation of their suffering, and seeming to suffer, the compresence of opposites. In the middle period, Plato seems to accept an account of perception that has as a necessary component the interaction of material elements. There may be subsequent or simultaneous psychic  activity,[13]  the judgment part of ‘perceptual judgment’, but there is at least some material intercourse between the body of the perceived object and the sense faculty whose sensory object it is. The qualifications needed to account for a particular's being F and not-F are temporal, or a function of being comparable to other extended material objects, or standing in different relations to  perceivers.[14]  Since material extension is a necessary condition for their perceptibility, no particular could appear to have compresent properties unless it were material.