23. Multiplicity and Order. The Idea of the Good. -- Faithful to this extreme realism, Plato gives a corresponding Idea-entity to each and every one of our abstract representations. Not only natural kinds or species of things, but artificial works; not only substances, but even properties, relations, grammatical forms; and, to complete the list, even negations and nothingness itself: all have their corresponding ideas in the suprasensible world.^{1}

The real world being modelled on the world of thought, the Ideas are hierarchically arranged like our representations of them. The Idea of the Good is enthroned at the apex of the ascending scale of essences. Plato lingers with an undeniable sense of complacency and delight in contemplating the Idea of the Good, the archetypal essence, "the sun of the ideal world".^{2} Its role is an all-important one, for it is: (1) the Final Cause of the Universe: the phenomena of the sense-world and the Ideas tend, all alike, towards the Good; (2) especially the Formal Cause of all things. All Ideas, even the Ideas of the True, the Just, the Beautiful, derive their intelligibility and their reality from the Idea of the Good, and have no being except from the Good. Logically followed out, Plato's realism seems to end necessarily in Monism.

{1} We have it from Aristotle that Plato suppressed, later on, the Ideas of negations, relations, and artificial works.

{2} See especially Republic, book vi.