The plenitude principle or principle of plenitude asserts that everything that can happen will happen eventually.
The historian of ideas Arthur Lovejoy was the first to discuss this philosophically important Principle explicitly, tracing it back to Aristotle, who said that no possibilities which remain eternally possible will go unrealized, then forward to Kant, via the following sequence of 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 somewhere else 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.
- 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.
- Kant believed in the Principle but not in its empirical verification, even in principle.
In physics, experimentalists became increasingly positive toward the many-worlds interpretation of quantum mechanics, ‘probably [because] they have recently produced so many “weird” (but perfectly repeatable) experimental results [...] and therefore simply accept that the world is a weirder place than we thought it was and get on with their calculations.’
- Arthur Lovejoy, The Great Chain of Being. Harvard University Press, 1936: ISBN 0-674-36153-9
- Chapter IV "The Principle of Plenitude and the New Cosmography", p. 99–143.
- Chapter V "Plenitude and Sufficient Reason in Leibniz and Spinoza" p. 144–182.
- Arist. Phys. III, 4, 203b25-30
- Caldecott, Stratford (Spring 2003). "Creation as a Call to Holiness". Communio. "God creates whatever exists because it is fitting, not because it is necessary to him, nor because he is constrained by something outside himself."
- Tegmark, Max (1998). "The Interpretation of Quantum Mechanics: Many Worlds or Many Words?". Fortschritte der Physik 46 (6–8): 855–862. arXiv:quant-ph/9709032. doi:10.1002/(SICI)1521-3978(199811)46:6/8<855::AID-PROP855>3.0.CO;2-Q.