Question. What is the name of the following position?

Everything that is possible, exists. Thus, in particular, every possible universe actually exists, as a concrete reality.

I don't mean Platonism, which adds the possibility of perfection into the mix and e.g. claims that there exists a perfect table, and a perfect chair, etc. I also don't mean multiverse physics; this isn't a theory of physics, its an ontological position, and postulates no particular relationship between different universes; in particular, it doesn't postulate that they're all part of a bigger space called the "multiverse" and can interact to produce new big bangs or anything like that.


Conifold's answer seems right on target. But if not, is the term you are thinking of Lewis's "Modal Realism"?

Also, though Leibniz seems to be saying the opposite, he does in some sense speak of an infinity of divinely "possible worlds" that "demand existence," but are necessarily reduced to one "actual" world as the "best possible" world that can "actually" exist, given God's optimal choices.

Like many things with a 17th-century baroque curvature, this seems almost to reflect into its opposite: the "maximum possible" actualization of all possibilities. Not what you were thinking of, probably, though not impossible.


This is called the principle of plentitude, namely everything that can exist does exist, see also SEP, the term was coined by Lovejoy in 1936. He does trace its roots back to Plato's Timeaus however, and takes Aristotle as rejecting it, "it is not necessary that everything that is possible should exist in actuality". During the middle ages it was a position that directly opposed the Occam's razor, "do not multiply entities without necessity", and Kant was at least sympathetic to it:"the variety of entities should not be rashly diminished".

The principle gained popularity among physicists in the 20th century, for instance the search for magnetic monopoles, black holes and wormholes was motivated by such ideas, and it is implicitly invoked in the anthropic principle explanations of the fine tuning of the fundamental constants, and other traits of our universe. Everett's multiverse also arguably appeals to plentitude rather than Occam's razor. The idea that anything not ruled out by the laws of nature is realized somewhere in nature is generally appealing to scientists, although perhaps more as a methodological ideal than an ontological principle.

  • According to Wikipedia: "The principle of plenitude asserts that the universe contains all possible forms of existence." That's not the position I'm referring to, unless wikipedia's definition of "universe" is completely different to how this term is used in modern science. – goblin GONE Nov 19 '15 at 3:08
  • Also, this term seems to be allied with the concept of perfection: According to Wikipedia, 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." No, I'm not talking about ideals or perfection. – goblin GONE Nov 19 '15 at 3:10
  • @goblin The term outgrew Lovejoy's Platonic associations, including his use of the "universe". SEP article doesn't even mention him and writes "More generally, a principle of plenitude claims that if it is possible for an object to exist then that object actually exists". – Conifold Nov 19 '15 at 18:19
  • I've come across the principle of plenitude when someone argues unconvincingly that since the Universe is infinite (by itself a big assumption), there must be an identical copy of the Earth somewhere "out there", on which an identical copy of yourself exists, etc. – RobertF Sep 7 '16 at 17:46
  • @RobertF Yes, it is standard to invoke plentitude for multiverse scenarios, and more generally to assume that if something does not contradict physical laws it is instantiated somewhere. scientificamerican.com/article/… – Conifold Sep 8 '16 at 17:52

The main contemporary philosopher that takes this position as pointed out elsewhere here, is Lewises Plural Worlds.

Aristotle, in his Physics VIII.1, notes that other philosophers in his time had taken such a position; but does not go into any details:

Some, however, claim that change is eternal; this is the view of all those who say that there are infinitely many worlds and some of these worlds are coming into existence, whilst others are being destroyed.

This, like Smolins notion of the Multiverse, is predicated on change being eternal as opposed to having an origin - which is the position Aristotle takes; though, it may be possible he is theorising the origin of one world amongst many.


You seem to be describing an extreme version of hard causal determinism:

  • Everything has a cause.
  • Each cause has only one possible effect.
  • Therefore the only things that have occurred are those that are possible, and anything that hasn't occurred didn't because it wasn't possible in the first place. There is only one possible causal chain back to the origin of the universe.

Laplace most famously formulated this idea in what later become know as Laplace's demon: If a super being knew everything there was to know about the universe in terms of velocities, masses and positions of each an every particle, then that being would be able to calculate all of the past events that have ever occurred and know all of the future, since there was only one possible past and one possible future per the laws of physics.

Note that this position isn't compatible with current results from quantum mechanics (whether Copenhagen or MWI, or any other non-hidden variable theory).

After comments from the OP, adding a second possibility (pun intended)

The idea that everything that is possible exists (at some point or the other), could be a reference to Nietzsche's Eternal Recurrence.

Eternal Recurrence is a fairly intuitive concept once you accept the basic premise (popular in the 19th century) that time is infinite, but space is finite. Finite space implies a finite set of possible configurations of the material world. If time is infinite, then the universe will go through every possible configuration it can have, and eventually return to a configuration it has already been through before.

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    Honestly I think it's not related whatsoever. I think his question is related to the mathematical fact that in an infinite series of figures that never repeats, like the decimals of PI, you can find absolutely everything. Which means, in an infinite universe, everything exists. Now the condition is that the universe has to be infinite for it to be true. – v.oddou Nov 19 '15 at 1:37
  • No. The position in which I am interested makes no reference to cause-and-effect, and it makes not physical predictions, and can neither be affirmed nor denied by experiment. It's a way of thinking, not a theory of science. – goblin GONE Nov 19 '15 at 3:20
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    @v.oddou it is not known whether every digit sequence occurs in the decimal expansion of pi, only conjectured. It certainly is not true for arbitrary infinite, nonrepeating sequences. – Matt Samuel Nov 19 '15 at 6:09

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