1. History. The idea, throughout all its changes of meaning, whether accepted or rejected, is one of the basic terms of Western thought, whose Unity and differentiation it displays in the most concentrated form. ’Ιδέα means first of all appearance, form, character. Plato uses it for the essence, first for that of the virtues in contrast to their distinctive modes of realization in the concrete, then for virtue as such and for the good in itself and the true reality of all beings. These essences (…