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Is there a philosophical notion that stipulates or proposes one of the following statements? Everything that can be imagined could also possibly exist. Everything that can be imagined must necessarily exist.

E.g. because imagining something automatically gives it certain properties of existence / makes it real. Or - and that seems to be fairly fashionable at the moment - everything that does not contradict the basic axioms of mathematics must exist in an ultimate multiverse.

Please excuse me if the explanation of my question seems a bit awkward. I am not at all experienced when it comes to philosophical concepts and would just like to learn a bit more on that topic as a captivating mental exercise. :-)

  • The second statement is ambiguous between: ‘necessarily, if something can be imagined, it can exist’ and ‘if something can be imagined, it exists necessarily’. The second is certainly false and the first is debatable. The question is usually phrased as: does conceivability entail possibility? There’s a lot of literature on this. A good starting point is: plato.stanford.edu/entries/modality-epistemology/#toc – MarkOxford Jun 13 '18 at 11:36
  • The question is particularly important in philosophy of mind, as arguments in that field often assume that ‘such-and-such a being is conceivable and hence possible’. Philosophical zombies are an example: plato.stanford.edu/entries/zombies – MarkOxford Jun 13 '18 at 11:36
  • "because imagining something automatically gives it certain properties of existance" ... specifically what ? What is the definition of "to exist" ? See Existence and Nonexistent Objects. – Mauro ALLEGRANZA Jun 13 '18 at 12:59
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Of the two ideas at play here one is epistemological the other ontological. The first is the imaginability-implies-possibility principle used in arguments for mind-body dualism, for example. Even supporters, like Chalmers, Kripke or Hart, see the inference as strictly speaking invalid but often plausible, a default to be accepted until shown otherwise:

"No-one would nowadays identify the two (except, perhaps, for certain quasi-realists and anti-realists), but the view that imaginability is a solid test for possibility has been strongly defended. W. D. Hart ((1994), 266), for example, argues that no clear example has been produced such that “one can imagine that p (and tell less imaginative folk a story that enables them to imagine that p) plus a good argument that it is impossible that p. No such counterexamples have been forthcoming…” This claim is at least contentious. There seem to be good arguments that time-travel is incoherent, but every episode of Star-Trek or Doctor Who shows how one can imagine what it might be like were it possible."

The second is Leibniz's counter-principle to the Ockham's principle of parsimony (do not multiply entities without necessity), the principle of plenitude: everything that can exist does exist, i.e. possibility implies existence. In the Leibniz's original version the rationale was that the best possible world God created would contain the maximum of possible entities, in a way it was an extension of Anselm's ontological argument's idea of existence as the highest perfection, which God must possess. A more cautious version was proposed by Kant: "The variety of entities should not be rashly diminished". A sarcastic parody of the principle is the "Murphy's law":"Anything that can go wrong will go wrong". The principle is popular with many theoretical physicists, for example Dirac alluded to it after working out the theory of magnetic monopoles:"one would be surprised if Nature had made no use of it". Ford stated it even more boldly:

"One of the elementary rules of nature is that, in the absence of laws prohibiting an event or phenomenon it is bound to occur with some degree of probability. To put it simply and crudely: anything that can happen does happen. Hence physicists must assume that the magnetic monopole exists unless they can find a law barring its existence."

One can see multiverse interpretations of quantum theory as expressions of the same idea (indeed it is a reification of Leibniz's "multiverse"), the controversial anthropic principle (our universe meets conditions for supporting intelligent life because otherwise it would not be observable) implicitly relies on a plenitudinal pool of universes "selected" for emergence of intelligence. But as one can see both principles are mostly offered as defeasible heuristics, not metaphysical postulates, accepted unless and until contrary evidence comes to light.

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Although I’m interested in philosophy, I’m not a philosopher either. But the statement “everything that can be imagined must necessarily exist” seems to be in the philosophical concept of “modal rationalism”. David Chalmers, the leading proponent of this concept has the view that conceivability entails possibility (please read about “modal rationalism” in The Epistemology of Modality and Modal Rationalism and the Mind-Body Problem).

But, personally, I don’t agree with this concept. For example, one can conceive of p-zombies (please see philosophical zombies and zombies-plato.standford.edu), but they can exist only in an imaginary world, not in a real physical world. This is because the definition defines an entity that cannot physically exist: a p-zombie is a being that is physically identical to a normal human except that it lacks qualia and conscious experiences. This is physically not possible.

This is because it is the same as we define that a p-zombie is a being that is physically identical to a normal human except that it lacks a pineal gland. This p-zombie is physically impossible to exist because when it lacks pineal gland, it will lack pineal gland effects too. The lack of pineal gland effects makes the phrase “identical to a normal human” impossible.

A human = a being + pineal gland + pineal gland effects

A p-zombie = a being + pineal gland effects (by definition, but physically impossible)

It’s obvious that this p-zombie cannot physically exist (pineal gland effects without pineal gland are not possible). In case of qualia and conscious experiences, just replace pineal gland in the above equations with qualia and conscious experiences. (This discussion and the equations are from p-zombies. And the proof that qualia and conscious experiences have physical effects can be found at 5.4. Effects of qualia in Chapter 5.)

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'Everything that can be imagined could also possibly exist.'

This claim faces a basic challenge :

The central question that must be answered to defend even this ... role for conceivability [imaginability] is why should it be thought that there is any connection at all between what we can or cannot conceive of [imagine] and what is possible. These seem to be two entirely distinct subject matters, one having to do with facts about what we can do in our minds, the other with facts about how things could be. Why should the fact that I can conceive of [imagine] something lead me to think it is possible? Why should we even begin to think that anything that is possible is such that we can conceive of [imagine] it?

Suppose, for instance, that you held that the laws of nature were necessary. Would one consequence of this view be the denial of the claim that we can imagine worlds in which the laws of nature are different? Would it really be surprising that, if the laws of nature were necessary, we could imagine them being otherwise? It seems to me that the necessitarian about laws of nature can simply say that, although we can imagine things being this way, things in fact cannot be this way. ( Paul Tidman, Conceivability as a Test for Possibility, American Philosophical Quarterly, Vol. 31, No. 4 (Oct., 1994), pp. 297-309 :306.

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Most directly, since imaginability, 'can' and 'must' are traditional modes, Modal Realism asserts what you are considering. But it does not determine an actual philosophical position. The question remains open what range of modes you want to take seriously as a point of reference and which mode you mean to consider 'real'.

Your two italicized conditions together constitute a 'mode' in the sense of modal logic. It is the mode of 'actuality'. The two boundaries are not really different, except for being opposite ways of putting the same thing. What we cannot say must not exist is exactly what could exist. But clearly even this is a point on a continuum. We do not mean these things are real in the sense of existing right here and now. Tomorrow morning is real in some senses, and not in others. So there is, in fact, a range of modes around 'the actual' that are not the same.

The notion of what can be imagined is another mode. We can imagine exactly what doesn't break down our ability to imagine it.

A concept of modal realism is the assertion that some two points on the manifold of modes are in fact the same, and the space between them is imaginary or misleading. Two extreme forms state that the whole range doesn't exist. That imagination is somehow physically determined and fixed in scope, having to accord in some way with our physical world, at one end, or that everything that we can even mention exists in the same way as the ground we stand on, at the other.

Imagined possibility in the sense of Kripke is a vague middle space in the realm of modes.

We can move up, bracing in our imagination with constraints and talk about what 'should' exist 'given...'. You can imagine the five ton ants from THEM!, but in reality those could not exist. They are not realistic: they should not exist given the rules of Newtonian physics. Their exoskeletons would not take the weight, they would all crack open and die before reaching this size, or their skins would have to be so thick and the poor things could get no oxygen. At the same time, we can predict a planet just half the size of earth, and be pretty sure this is realistic, even if we can't go out and find one. (And you can move 'up' in slightly different directions, imagining say the facts of physics are facts, and the facts of psychology or chemistry are not. So this is not really just a spectrum, but it is largely so.)

There are people who admit worlds as 'possible' only if they satisfy the requirements of all know and future science. If you add history, observed and unobserved, and you accept determinism, you get the position where this is the only possible world.

We can also move down and talk about what 'would' exist 'if only...'. Things can be considered hypothetically or wished for which may not make sense. For example, When mathematicians consider something like the hairy ball without a cowlick, it is ambiguous to what degree they are actually imagining it, since it is actually inherently self-contradictory. But they are doing something. They are processing it in some way despite its potential (in this case provable) nonexistence. For the duration of the proof of its own inconceivability, it is in some way 'real', in order that we can do the mental actions to it that lead us into the contradiction... And it would be equally so whether we found that contradiction or not.

There are people who demand all of these things are also real. David Lewis has tried to rationalize this position. Meinong has gone way beyond it. Then we have to worry about what modal point they chose to imagine they meant by real. I am not going home to purple unicorns this evening...

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