Principle of plenitude

Principle that if the universe is to be as perfect as possible it must be as full as possible, in the sense that it contains as many kinds of things as it possibly could contain.

The world of nature must be as rich as possible. This is connected with the idea, used by St Anselm (1033-1109) in his ontological argument for God’s existence, that existence is a perfection.

Another version of the principle refers to events rather than to kinds of object. It says that there can be no possibilities that remain as possibilities (and are not foreclosed) but are unrealized throughout eternity; in this form, which goes back at least to Aristotle (384-322 BC), the principle is given some credibility by PROBABILITY THEORY: the probability that the proverbial monkey at a typewriter will type a Shakespeare sonnet straight off may be minute, but if he remains typing for long enough the probability increases indefinitely and it becomes increasingly surprising if he does not type one.

A O Lovejoy, The Great Chain of Being (1936)

The principle of plenitude asserts that the universe contains all possible forms of existence. The historian of ideas Arthur Lovejoy was the first to trace the history of this philosophically important principle explicitly. Lovejoy distinguishes two versions of the principle: a static version, in which the universe displays a constant fullness and diversity, and a temporalized version, in which fullness and diversity gradually increase over time.

Lovejoy traces the principle of plenitude to the writings of Plato, finding in the Timaeus an insistence on “the necessarily complete translation of all the ideal possibilities into actuality”.[1] By contrast, he takes Aristotle to reject the principle in his Metaphysics, when he writes that “it is not necessary that everything that is possible should exist in actuality”.[2]

Since Plato, the principle of plenitude has had the following adherents:

  • Epicurus reiterated the principle in fr.266 Us. His follower Lucretius (DRN V 526-33 ) famously applied the principle to the sets of multiple explanations by which the Epicureans account for astronomical and meteorological phenomena: every possible explanation is also true, if not in our world, then elsewhere in the infinite universe.
  • Augustine of Hippo brought the principle from Neo-Platonic thought into early Christian Theology.
  • St Anselm’s ontological arguments for God’s existence used the principle’s implication that nature will become as complete as it possibly can be, to argue that existence is a “perfection” in the sense of a completeness or fullness.
  • Thomas Aquinas accepted a modified form of the principle, but qualified it by making several distinctions that safeguard the freedom of God.[3]
  • Giordano Bruno’s insistence on an infinity of worlds was not based on the theories of Copernicus, or on observation, but on the principle applied to God. His death may then be attributed to his conviction of its truth.
  • Spinoza, according to Lovejoy, “expressed the principle of plenitude in its most uncompromising form” and “represented it as necessary in the strict logical sense”.[4]
  • Kant believed in the principle but not in the possibility of its empirical verification.
  • Leibniz believed that the best of all possible worlds would actualize every genuine possibility.

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