This question arose during contemplation of whether free will and/or moral responsibility might ever be proven real or illusory.

Galen Strawson has proposed a proof for the impossibility of moral responsibility, which also seems to address the impossibility of free will. Another accessible argument against free will can be found here.

Suppose for a moment that these arguments are robust. Is logical argument alone ever enough for us to accept claims which can't (yet?) be demonstrated?

Cosmologists employ physics and math to develop highly accurate predictions which - when/if proven true - change our understanding of the world. But do we accept any of these theories (eg: the existence of black holes) before we observe their existence?

Are there any instances of humans accepting consequential claims (claims which impact the ways in which we think about the world and/or operate within it) via logic alone; in the absence of observation?

Mathematical proofs are of interest, but primarily insofar as they might demonstrate less abstract/complex truths.

(By 'observation', I'm referring to phenomena which might be observed scientifically, not merely by the naked eye).

The answers might well be obvious to many in this community, but I'm just a beginner and I'm hoping this question will be of broad interest.

  • 4
    Logical arguments are demonstrations, and are always enough for us to accept their conclusions. That is, if we accept the premises first. That no "consequential" premise about the world comes out of "logic alone" is another matter, and Strawson's "nothing can be causa sui", etc., is no exception. As for humans accepting consequential claims "by logic alone", they have been accepting them even by no logic at all, in large numbers, just look at most Russians right now. Or, more academically, at Aristotle's surmises about the rock and the feather, or Kant's about Euclidean geometry.
    – Conifold
    Commented Jul 20, 2022 at 9:10
  • 1
    @Conifold. I agree re. your observation, "by no logic at all" (although a rationale of sorts still exists in much of such thinking). Re. always accepting conclusions though, I'm interested - as one example - in whether the logical proof (if it existed) for a black hole was deemed 'enough', or was the observation required? Commented Jul 20, 2022 at 9:42
  • 1
    A "logical proof" cannot exist in principle, it is a non-logical concept. There could be, and was, a mathematical proof, sort of. First, Michell derived the possibility in Newton's theory, and, over a century later, Schwarzschild in general relativity. But no, most physicists did not believe in them until credible empirical candidates were found in 1970s (Cyg X-1). As well they shouldn't have. Such a proof is only as good as the empirical theory it is based on, and, in this case, at the edge of its applicability, at best. Dirac's "by logic alone" magnetic monopoles are still disbelieved.
    – Conifold
    Commented Jul 21, 2022 at 3:30
  • 2
    Btw, I think the term you are looking for is not "by logic alone" but a priori. And I would say that there is largely a consensus today, in analytic philosophy at least, that a priori knowledge of the world, in the non-relative Kantian sense, is not available to us. This does not rule out practical certainty based on projecting integrated past experience, about non-existence of perpetuum mobile, for example.
    – Conifold
    Commented Jul 21, 2022 at 3:38
  • Are you Asking there for anything more than a simple list? Commented Jul 29, 2022 at 21:04

8 Answers 8


We use logic to convince ourselves or each other that something is the case without going the extra mile of obtaining direct empirical evidence.

Most people routinely rely on logical inferences to make choices in their everyday life and modern science and therefore modern technology heavily rely on logic, but anyone is free to dismiss logic out of hand and require direct evidence, though I am not sure I know anyone really trying that.

The routine acceptation of logical arguments to make choices in life is a pragmatic move. It save time and energy. It saves a lot of time and a lot of energy. As such it improves our chances of survival, our prosperity, and our prospects of reproducing ourselves. Not just a little bit. A lot. People who dismiss logic out of hand will on average fare no so well, and mostly seriously less well, at least on time scales we are familiar with.

Direct evidence is also nothing like incontrovertible evidence. You wouldn't know God exists if you were looking at him. What you see is not the thing in the world outside your mind you think you are looking at. It is only at best the visual percept only presumably caused by the thing in question. Yet, we normally accept this as sufficient evidence that the thing exists and that it is essentially as we see it. Until science comes along and proves to us that things are really very unlike what we think on the basis of our percepts. We have direct evidence that that the Sun turns around the Earth. We can verify this everyday that we are alive and the Sun is shining. This would be confirmed by 8 billion human witnesses. Yet, science tells us, this is not true.

Human beings can only accept and rely on logic because there is nothing else available to the human brain to work out what the real word is. Direct evidence is itself the indirect product of cryptic cognitive processes taking place unconsciously inside our own brain, a brain of which we ourselves usually have no direct evidence that it exists.

We use logic because there is nothing else we could use. The alternative is just extreme scepticism and nobody really wants to try that.


Suppose for a moment that these arguments are robust. Is logical argument alone ever enough for us to accept claims which can't (yet?) be demonstrated?

In the limit case, an individual, as far as I'm aware, can only be certain that they are experiencing something. So to be convinced that one exists in a shared reality with other individuals requires logical argument.

So in that case, I personally find that logical argumentation alone is sufficient to accept a claim. I may not be absolutely certain of that claim, but I'm certain enough that I behave as if that claim were true.

  • 2
    Yes. I tend to agree. It's the way we navigate much of life, as @speakpigeon points out. I guess I was wondering in particular about any 'big' discoveries that have impact upon as all. Ie: Have/do any of these relied/rely upon argument alone? Commented Jul 20, 2022 at 14:41
  • 1
    @Futilitarian that depends on what we mean by "discovery". One could say that philosophical schools or religions are generated by argumentation alone and have had a broad impact.
    – philosodad
    Commented Jul 21, 2022 at 2:10

Are there any instances of humans accepting consequential claims (claims which impact the ways in which we think about the world and/or operate within it) via logic alone; in the absence of observation?

Yes and no. I mean a rather significant amount of our "knowledge" doesn't stem from direct personal experience but from hearsay and "what if" scenarios. Just think about all the ways to die that you know and that you haven't experienced first or even second hand.

So yes we do that all the time. At the same time we don't really do that. Like fully accepting it would mean that we give these things the status of a fact and treat it en par with empirical evidence and first hand experiences and while some people do that, we rather treat that as a disorder then as a sane reaction. Like if you were to discard reality in favor of a theory you'd be labeled insane, so our acceptance for that is limited.

We're rather "agnostic" towards these questions. Meaning as long as we aren't actually effected by these problems, it's kinda irrelevant to us so we might as well accept the consensus or the logical derivation as an ad hoc truth or expectation without being married to it. But once we actually make the observation and are able to actually determine the truth value, we'd not hesitate to revoke our acceptance. While we wouldn't or shouldn't do the same with empirical evidence.

  • 1
    Can you think of any examples of such instances? (Real or imagined is fine). Commented Jul 20, 2022 at 11:43
  • 2
    Religions, Philosophy and as a consequence political movements. How we trust science enough to employ it in engineering, medicine and other domains where the consequences might very well kill us.
    – haxor789
    Commented Jul 20, 2022 at 11:51
  • Religions might very well kill us also, which would be ironic.
    – Scott Rowe
    Commented Jul 28, 2022 at 1:05
  • Really, Scott? How might religions kill us and if they did, how might that be ironic? Commented Feb 13, 2023 at 20:37

Is logical argument alone ever enough for us to accept claims which can't (yet?) be demonstrated?
Everyone is in agreement that logical arguments can lead to acquiring knowledge. The issue is about where the premises, the starting points of a logical argument, come from.

Knowledge that we can deduce before making any observation of the world is called a priori [Latin for 'from what is before']. Two really good examples of a priori knowledge is that "2 + 2 = 4" and "All bachelors are unmarried males." We do not need to observe anything or run any experiments to know that these statements are true; all that is necessary is to understand what the words mean and then to think about them.

The rationalists hold that a priori knowledge is where the premises for a sound argument come from. The empiricists disagree and hold that that sensory experience is where premises come from.

In truth, reputable philosophers always subscribe to positions somewhere between these two extremes and a single author can change between rationalism and empiricism depending on what type of knowledge is being talked about (e.g. Locke claimed that a priori knowledge of morality exists, but not the properties of materials).

But do we accept any of these theories (eg: the existence of black holes) before we observe their existence? Are there any instances of humans accepting consequential claims (claims which impact the ways in which we think about the world and/or operate within it) via logic alone; in the absence of observation?
This is a really interesting question that I am not less sure about. It seems to me that you made a subtle, but massive, change from asking about knowledge to asking about belief. The biggest difference between knowledge and belief is that knowledge is always true, but beliefs are not. For example, lets pretend that a person named Alice released a video about how the Earth is flat. We would confidently say that "Alice believes that the Earth is flat," but we would not say "Alice knows that the Earth is flat."

Personally, I would answer yes, a person can accept belief a "consequential claim" even if there is no empirical evidence supporting this claim. My reasoning is that conspiracy theorist do adopt beliefs and make significant changes to their lives based on those beliefs, even though empirical evidence supporting the conspiracy theory is lacking.

  • Very useful. Re. your 2nd section, you've made me realise I should probably have been clearer, in that by 'the ways we think about the world', I was talking more about claims less at the level of conspiracy theory than at the level of broadly/close-to-universally accepted 'knowledge'. Then again, maybe I'm asking for something non-existent, ie: a scientifically-accepted claim that does not rely upon observation. Commented Jul 21, 2022 at 8:09

The case of black holes is illustrative of the conclusion I am going to offer, so I'm going to dwell on this case to some extent. Now, one might construe our knowledge of black holes as having been a priori in the sense that, before we ever "saw" one, we predicted their existence because the possibility of this existence was as a possible solution to certain deep equations that we accepted (albeit on empirical grounds, so to speak). One interlocutor in such a dialectic might object that making a true prediction is not tantamount to advance knowledge, due to the epistemic nature of predictions. They might quibble that we had "preknowledge," but not knowledge strictly, of black holes, up until recently.

The next counter might be that, besides knowing of black holes' general possibility via the relevant equation-solution, we also were aware of specific dynamics, in our world, that might form them, i.e. stellar evolution over sufficiently massive stars. But then a fringe (hopefully not pseudoscience) researcher might come along and say that our current more "direct" black-hole knowledge is consistent with the possibility of eternally collapsing magnetic objects, and appeal to the alleged theory-ladenness of observational evidence to defend the suggestion philosophically. Similarly, though the prevailing model of active galactic nuclei is as a function of supermassive black holes, there are outliers who ask after boson stars as an alternative model. And then an ecumenicist in physics, so to speak, might go on to propose that black holes are boson stars made of gravitons; or that black holes and other types of boson stars are both possible and might be the AGNs of different types of galaxies.

So for all that, how much apriority was involved in knowledge/preknowledge of black holes? All the "pure reasoning" in defense of these objects was not so pure, after all, requiring empirically-supported priors of various kinds (e.g., again, our largely empirical understanding of stellar dynamics).

But just the same, then, since there was apriority as epistemic proactivity involved, it ends up looking like Kant was on to something in trying to harmonize the motives of rationalism and empiricism. Since "the point generalizes," we might find ourselves thinking that very little is known in total abstraction or entirely due to physical experience ("Necessarily X means not possibly not X," as a representative example on one end, "I am having red-gradient color perceptions right now," on the other).

For technical reasons, I do think ethical knowledge, such as it is (or is supposed to be), would have to be heavily a priori, its empirical supports limited pretty much just to immediate perceptions, on pain of having to derive action-guiding principles from epistemically difficult claims. The old (discredited) notion that the fact of evolution justifies Social Darwinism hearkens to a commandment that Kant said was analytic, viz. "Act according to the truth." So the Social Darwinist would reason that contrary moral perspectives involved acting against the truth of evolution; and we find such specious thoughts in many a moral theorist's repertoire. Whence the speciousness, here? Just in that, if local moral imperatives are connected to universal, eternal moral facts, we'd best not have to learn the latter only after fairly complex observation and research: or else, with respect to evolution (say), we would be asserting that people were obligated to "act according to the truth of evolution" (or whatever) even when unaware of the process. (This is of a piece with the mainline objection to standard formulations of utilitarianism requiring us to perform overly elaborate future-oriented calculations of universal utility functions, which are not practical for us to perform.) But this leaves us with having to be able to recognize moral information a priori; yet if moral principles involve a proactive capacity inside us, and if apriority just is epistemic proactivity, what we are left with is something almost "true by definition" indeed (hence Kant's derivation, in the second Critique, of the categorical imperative).

  • I hadn't considered ethics when writing the question. Very interesting. Commented Jul 27, 2022 at 13:26
  • 1
    We establish moral judgements by a combination of intuition and applying a moral theory. Intuition is not a priori. It is instead non rational or non conscious detection and inference. The detection is direct rather than indirect realism, hence works differently than most empiricism, but it still is empiricism.
    – Dcleve
    Commented Jul 27, 2022 at 21:54

The short answer is “no”. Philosophers have basically concluded that our world is contingent, and a priori reason cannot tell us what our contingent world will look like. This was the main point of Kant’s The Critique of Pure Reason.

Note Kant separated out a few exceptions, of which he considered Euclidean geometry the exemplar case. Soon afterwards we learned that our universe is not actually Euclidean, so “no exceptions” is now consensus.

More details:

Kant also believed in One True Logic. Current logician views are that logic is pluralist. So — one can postulate a specific logic, and a set of premises, then show that derivations from those premises are true in that logic. But that does not mean that logic applies to our world, either in general, or in one specific instance. Derivations need to reference both the premises, AND the logic set used to do the derivation.

Black Holes. These were not a priori. They were derived, using classical logic, from the Standard Model of Quantum Mechanics. The Standard Model is VERY empirical, it is not based on a theory. The derivation was by noting that gravity is weak, but sums to infinity, while the other stronger forces are short range and cancel out. Hence gravity could eventually overcome the repulsion of the Strong Force, collapsing all matter.

A counter empirical observation is that no singularities had been seen in the universe, despite singularities being easy to create using math and logic. All prior singularities were prevented by some discovered addendum to a general science law, so most physicists assumed that some addendum to the Standard Model would prevent black holes, because the universe does not actually do singularities.

These were two competing theoretical predictions, based off prior empirical evidence. Basically, few physicists expected black holes to exist, as the “no singularities” inference was considered far more reliable. Plus QM often does not follow classical logic, so that was a second black mark for black holes. But now, with empirical evidence, “no singularities” has been refuted, and basically all physicists accept black holes


If I have to start from some premise, I might as well start from the premise that it matters whether what I believe is true.

If I believe that it does, and I’m wrong—what does it matter?


What difference could there be between "(most) important" and other claims?

Do you not think "What, if any, are the most important claims to be considered proven in the absence of observation; ie: claims derived from logic alone…" is up to the author - here, up to you - to explain?

When the question arose during contemplation of whether free will and/or moral responsibility might be proven, did you see no difference between free will and moral responsibility? Did you see it but dismiss it?

If you want to Ask about Galen Strawson's views on the impossibility of moral responsibility, why not Ask about that?

If you think Strawson's views on the impossibility of moral responsibility matter, why not Ask about them?

If Strawson's views address free will or responsibility, why not say how?

If "… another accessible argument against free will…" doesn't reveal bias, why not explain how?

Logical argument is often enough for acceptance of many claims; so what?

Who understands the arguments broadly does accept the theories you hinted at, eg, the existence of black holes, before observing anything. So what?

"Science" is riddled with instances of consequential claims impacting the way we think about and/or operate within the world via logic alone, in clear absence of observation. Why does that seem strange?

When the answers might be obvious, why not show what research you did and where that let you down?

The Question is of broad interest but not,I suggest, in a way relevant or even permitted here.

  • I see no difference between free will and undertaking responsibility.
    – Scott Rowe
    Commented Jul 28, 2022 at 0:47
  • 1
    @ScottRowe You might not see it and you might not care if you did, yet part of the difference is that free will is a tool that might be used to achieve the goal of undertaking responsibility. Commented Jul 29, 2022 at 20:50
  • Ok. I guess it's like the difference between a hammer and hammering?
    – Scott Rowe
    Commented Jul 30, 2022 at 21:29
  • @ScottRowe If that's as close as you can get, go for it! In fact, it's like the difference between the hammer and the object being hammered, not the action of hammering. Does that not work for you? Commented Jul 30, 2022 at 21:46
  • Well, I tend to think in terms of action, not things, verbs instead of nouns. So, "taking responsibility" is something I can relate to, but "free will", as a thing rather than an activity, is just a noise. Things don't really exist as such, so we shouldn't waste so much time nailing them down. Max Tegmark said, "Intelligence is the ability to accomplish goals." If a computer can win at GO with no ideas or definitions, I think it backs up my assertion. Animals can be intelligent without using symbolic logic.
    – Scott Rowe
    Commented Jul 31, 2022 at 12:44

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .