Some 60 years ago, Arthur O. Lovejoy in his famous work The Great Chain of Being proposed to sketch the history of an idea, one he saw as permeating Western thought. The idea Lovejoy dubbed "the principle of Plenitude"; he gave to it the single, deceptively simple formulation that "no genuine possibility will remain forever unrealized". The idea is as classical as any that can be imagined. Lovejoy himself proposed to trace the principle's origins in Plato's cosmology; he went on to point out its workings in Neoplatonist theodicy, in medieval Christian thought and in seventeenth- and eighteenth century metaphysics, to name but a few examples. And subsequent studies have expanded on Lovejoy's insights.1
Though Lovejoy took the principle of Plenitude to be a "unit idea", he distinguished between two basic forms. One involves a maximality of possible kinds of beings, a kind of continuous ontological scale; the other is the temporalized notion of all particular possibilities being realized within the whole of (infinite) time. What Lovejoy took to be two sides of the same coin in fact incorporates a whole range of approaches towards the relation of the possible to the actual.2 A Plenitude of species has, first of all, the dimension of all possible Forms being realized in the divine mind, and then of them all having at least one instantiation in the visible world. The next more specific level comes with the question about whether all possible beings, and possibly all their possible qualities, are maximally realized at any one moment. An affirmative answer provides a further theme in the idea of a Plenitude in creation, one much used in theodicy. Finally, there is the strict temporalized notion according to which the very meaning of something's being possible is equivalent to its sometime being realized. Whereas all the other variations of Plenitude I have mentioned here are Platonic in origin this last one has different, largely Aristotelian origins. It finds its most clear explication in certain early medieval interpretations of Aristotelian modal theory that might be termed "statistical" or "frequential".
These different shades of Plenitude are not necessarily mutually exclusive, but neither are they mutually implicative (contrary to what Lovejoy thought). This becomes clear when one examines the history of a popular notion closely related to statistical Plenitude, that of the eternal being in some sense necessary. What I am attempting to trace is the gradual deterioration of this idea. The introduction of contingency into the eternal was, I will argue, the product of new kinds of modal theoretical ideas being injected into the
Aristotelian framework, ideas which paradoxically had their roots in another variant of Plenitude—the Platonic one of a maximal creation. There was, to be sure, at first no felt conflict between the views: only gradually did it become apparent that frequential necessity and emanationist necessitation do not necessarily gel. In the process, a heightened awareness was brought to bear on the theological problems inherent in the idea of an eternal and unqualifiedly necessary world. Belief in a strictly finite creation in time and/or in an ontologically depicted dependency relation then emerged as the most viable options.
All this is brought out nicely when we examine the evolving interpretation of Aristotle's so-called infinite power argument. Infinite power, in Aristotle ostensibly a purely kinetical notion, came to be understood as a divine attribute with far more wide reaching implications. This made the notion a particularly useful tool in arguing for a specific view of divine creation; Aristotle's proof for a First Mover could then be interpreted in temporal or atemporal, finitist or eternalist, naturalist or emanationist fashion. A look at Averroes' (1126-1198) struggles with the interpretation of the infinite power argument helps point out several key stages in the argument's remarkable history; it also spotlights the argument's ties with the different variants of Plenitude and conceptions of creation involved.3
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