There is a perennial philosophical question about whether the “ultimate reality” (which means more than one thing) is static or dynamic. The debate spills over into politics (should our laws be fundamentally immobile, or should they strive to constantly change with the times?) into biology (does evolution show that any stability in species is merely apparent?) and it certainly can’t be kept out of theology (process theology represents one extreme in the debate). In the ancient world, Parmenides advocated the static nature of ultimate reality, whereas Heraclitus more appreciated the unstable character of at least some ultimate things (Heraclitus never advocated a completely universal flux, but he did appreciate the unstable character of things in a way that others did not).This dispute comes to an impasse in Plato, who argues both for the utter stability of ultimate things as forms; and for the dynamism of ultimate things as products of soul, which is essentially self mobile.
Aristotle’s great insight into this debate was that stasis or dynamism did not of themselves have the characteristic of being ultimate. What is ultimate is what is complete or perfect, and stasis or dynamism are only perfect relative to the thing that is static or dynamic. Dynamism is good for joints and bad for bones; stasis is good for a knife edge and bad for a heartbeat; and at different times stasis and dynamism might be good for the same thing. For Aristotle, what is ultimate just is perfection. Perfection- which of itself and in its very notion transcends and contains both stasis and dynamism- is the ultimate ground of things. This perfection, which St. Thomas tended to call actus but which he repeatedly insisted was a synonym of perfectio, is the absolute bedrock of Aristotelian-Thomistic thought. There is simply no other concept underneath this one.