Is every feature of the universe logically necessary? For example, it would be logically necessary that no material object can exceed the speed of light. In other words, there is only one way for the universe to exist, by pure logic alone. What is the name of the view that everything in the universe is logically necessary, and have any philosophers argued for that view?

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    Logical necessity is about arguments, not about material objects. Jan 18, 2023 at 7:54
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    @Rodolfo Wrong. Logic is not tautological. At the base exist observation. Philosophy is not circular reasoning. You have to start somewhere. That somewhere is observation.
    – Atif
    Jan 18, 2023 at 9:17
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    @RodolfoAP -- Kant's claim to apriori knowledge of logic and math was decisively refuted when his go to example, Euclidean Geometry, was shown to not only not be necessary, but not even true of our universe. Math and logic are infinite, and which ones apply to parts of our universe are contingent observations.
    – Dcleve
    Jan 18, 2023 at 14:21
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    Logic is like a machinery that guarantees the validity of deductions w.r.t. some rules of the game (that we can change!), but it doesn't have a semantic content of its own. In FOL, a given formal language can have many interpretations in various structures.
    – Frank
    Jan 18, 2023 at 16:02
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    The entry you point to contains: "in the sense that logical necessity entails metaphysical necessity, but not vice versa, and metaphysical necessity entails physical necessity, but not vice versa" which seems to me to indicate that we are going to move from logic to claims about physical things.
    – Frank
    Jan 18, 2023 at 20:05

7 Answers 7


Logic is not in the business of telling the universe what to do, or even in the business of describing how the universe works. We have science for that. Logic is concerned with the relations of consequence between sentences. Arguably, there is nothing necessary about how the universe works at all. However the universe does happen to work, if it is able to support intelligent life, then rational beings would devise some way to describe it.

Our universe seems to operate pretty reliably and it can be described, at a fundamental level, by fairly few and fairly simple equations. But this does not make anything necessary. The fact that no motion exceeds the speed of light in a vacuum in our universe is, for all we know, just a property of our universe. Maybe it could have been otherwise. Maybe there are other universes where it is otherwise.

As to the view that everything in the universe is necessary in some fashion, this has been held by some rationalist philosophers. Leibniz comes to mind. He thought that God was constrained to create the best of all possible worlds, and so that is what our universe is, and it could not have been otherwise. Whether it is plausible to suppose that this is indeed the best of all possible worlds, I'll leave it to you to decide. Spinoza also claimed that God is necessary and that there is nothing contingent in nature, since everything is determined by the necessity of the divine nature.

Philosophers in the English speaking tradition of empiricism and analytical philosophy have usually not found such claims compelling.

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    I think that point needs reinforcement: logic is "subject-side" and doesn't say anything about nature. For that, you need to probe nature, which is "object-side". Inferences about nature based on logic alone have no epistemological value. They need to meet reality to be verified.
    – Frank
    Jan 18, 2023 at 15:56
  • "The optimist says, 'this universe is the best one possible'. The pessimist... agrees."
    – AnoE
    Jan 19, 2023 at 12:05
  • The weird thing is, there isn't even any logical reason why logic should work. It just does. Jan 19, 2023 at 18:54
  • @MichaelKay Every now and then we get a question on this site about whether it is possible to justify or explain why logic works. It is an interesting question. You might like to look at Conifold's answer to this question: philosophy.stackexchange.com/questions/47819/… and my answer to this question: philosophy.stackexchange.com/questions/52158/…
    – Bumble
    Jan 19, 2023 at 21:58

There is a saying in physics that is called the totalitarian principle (of physics), which holds that anything not expressly forbidden is compulsory.

  • Boltzmann brain has entered chat.
    – Joshua
    Jan 18, 2023 at 18:48
  • Eventually compulsory?
    – RonJohn
    Jan 19, 2023 at 0:09
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    en.wikipedia.org/wiki/Totalitarian_principle "compulsory" in the sense that it has to be included in calculations involving all possibilities of something. Plus of course all the satirical implications.
    – AnoE
    Jan 19, 2023 at 12:08
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    Even if it is, it is a property of the physics of the world we live in; it is not a logical necessity. Jan 19, 2023 at 12:29

The opposite of your presumption is the case. NO feature of our universe is necessary.

All the principles of logic we use, are discovered. There are infinite logics, different ones of which approximately apply to different aspects of our world. Logic itself is therefore contingent, not necessary.

All the laws of our universe are regularities, based on symmetries, which can and do spontaneously break. What those symmetries are, is a contingent feature of our universe. They could have been different. They were not discovered thru reasoning, but by observation, then fitting models to the observed data.

Our current physics is derived from the Standard Model of Quantum Mechanics, which is combined with cosmology observations, leading to approximately 30 contingent constants that our physics is based on. Current physics thinking is that ALL of those 30 constants could have been different. IE our universe is entirely contingent, not necessary.

This leads to one of the more philosophically noteworthy consequences of physics/cosmology -- the vast majority of the range of those constants would have prevented there being any life in our universe. This is the Fine Tuning Principle -- our universe seems to have been finely tuned for life to exist in it, within the very wide contingent range of physics we could have had. This observation has been seized upon by theists, and atheists have instead been forced to adopt a Multiverse assumption, to which they then apply the Anthropic Principle.


If we assume for a moment that space is a 'thing'; a definable system (whether closed or expanding), then:

Were we to have sufficient powers of description, we would be able to describe - for any given moment - every feature contained within that space.

If any feature - no matter how small - of that space were removed, the precise nature of the entire space would have changed. Any complete description (no matter how minute the change) would be different. The space previously described would no longer exist and a new description would be made necessary. In this sense (to state the obvious), every feature of the universe is necessary to satisfy any description which contains those features.

Every aspect of space - as far as we know - exists in some relation to every other aspect of space (whether close/maximal or distant/minimal). Therefore, if we were to remove (rather than merely modify the arrangement of) some feature of a given space without replacing it with a perfect replica, then the space it used to occupy (a vaccuum) would need to be filled, and this 'filling' would bring about a change in relationship (from the proximal/dramatic to distal/near-insignificant) between all other aspects of space. This change in relationship would not only be spatial, but energetic, for as spatial relationships change, so does the interaction and distribution of relevant energies. A new 'space' would now need to be described, for the quantity of energy necessary to any description of the old space would no longer exist.

In this broad sense, the universe could be described as simply a precise, conserved quantity of energy; a system that has no necessary features; only a necessary amount of energy that is perpetually undergoing spatial rearrangement.

Or, to look at it from a deterministic perspective, there's an argument that the universe at any moment in time could not exist in any other form than the way it is. In this sense perhaps, every feature is necessary. Again, a universe with different features would be a different universe.

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    Our universe cannot be characterized in its state at any point in time, due to Heisenberg Uncertainty Principle. The conservation of energy is a regularity, based on a symmetry which we know to be spontaneously broken, and which is inapplicable at high slopes of time/space change -- so no, conservation of energy is not an absolute for our universe. Plus physics is not deterministic -- for all physics there are cases with multiple solutions to the equations. See philosophy.stackexchange.com/questions/68224/…
    – Dcleve
    Jan 18, 2023 at 14:16
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    It depends what you require of the characterization. For a strong version of characterization, you will meet the HUP. For a weaker version, say, the positions of all the stars, or an approximate characterization, the HUP might not be a blocker.
    – Frank
    Jan 18, 2023 at 16:00
  • No man ever steps in the same river twice.
    – RonJohn
    Jan 19, 2023 at 0:17

Reality is what it is and is not conceivably constrained by the logic of homo sapiens.

However, if you are logical, once you assume that some description is true of reality, then you have to accept that whatever follows logically from the description is necessarily true. This does not mean that whatever follows logically from the description is necessarily true, it just means that if you accept the description as true, then if you want to be logical, you have to accept that whatever follows logically from it is necessarily true.


This question seems to hinge on the anthropic principle.

One interesting observation of physics is that several of the fundamental ways of how the universe works need to be exactly that way, or the universe would be so radically different that it would not be able to develop intelligent life like us that is capable of thinking about how the universe works. This includes things like the number of time and space dimensions, the relative strengths of the four fundamental forces, the ratio of gravity to dark energy, the cosmological constant and many more.

The theists of course love to jump on this and claim it as an argument for the universe being intelligently designed. But that is a sharpshooter's fallacy. The anthropic principle does not postulate that an universe with different properties could not exist at all (although in some cases it might be a very short-lived universe). It only postulates that an universe with intelligent life couldn't exist in a way that is very different from our universe. (or at least one with "intelligence" or "life" as we understand it, which are also topics where the debate is anything but concluded).

We don't know how our universe came to be. We don't know if it is the only universe that exists, has existed or will exist. Because if they exist, then there is no way to interact with other universes (that's the definition of "universe"). Which makes the question about their existence meaningless for anything but thought experiments. So did our universe turn out that way by chance? It might have been unlikely, but it obviously did, because otherwise we wouldn't be here.


X is logically necessary if ~X entails a contradiction.

Is there any feature in the universe, which if it were not the case, entails a contradiction?

The Statue of Liberty, did it have to be NYC?, did it have to be built? I see no logical necessity anywhere i.e. the Statue of Liberty being in Ghana or never having been built at all don't imply a contradiction.

However, there's Determinism, a philosophical position that the past decides the present decides the future. If true it implies there's no way other that the way it is for the universe to be i.e. the universe is logically necessary, every state it's in is determined by a state preceding it and that state by another before it ... ad infinitum. Similarly the future consists of effects whose causes are in the present. Determinism means every state (effect) of the universe is logically necessary given the antecedent state (cause).

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