There are certain claims that I accept as obviously true without (much) evidence. For example:

  • Most people don't like to be hit on the head with a hammer.
  • Donald Trump ate dinner some time last week.
  • There has yet to be a whale on the moon.

I don't even feel a need to find evidence before accepting these claims. But if someone decided to challenge me for evidence to support these claims, I would be hard pressed to come up with any. I could probably come up with some "thought exercises" to argue these things are true, but no empirical evidence.

These claims are also fairly inconsequential. If I'm wrong about such claims, it simply doesn't matter.

Question: Why do I accept some inconsequential claims as "obviously true" without evidence?

  • Comments are not for extended discussion; this conversation has been moved to chat. – Geoffrey Thomas Feb 20 '20 at 19:11
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    It takes energy to chase evidence. If one were to refuse to accept anything as an interim truth without evidence, one would be paralysed from the hundereds of micro-claims one faces daily. When the stakes are high enough, people feel the need for further research, to upgrade and solidify those interim truths. The default is acceptance, not rejection. – Rohit Feb 21 '20 at 14:21
  • I don't think the hammer example is a good one. Do you really lack evidence to support that belief? – Philosopher of science Oct 11 '20 at 13:18

First, because they are "inconsequential". Nothing hangs on it for you, there is no need to act on them and accept the consequences also, it is a "cheap", easily swayable "acceptance". But this still leaves the question as to why accept rather than reject, as easily, perhaps at random.

Which brings us to the second because: they are not accepted without much evidence, there is plenty of evidence for them, in fact. It is just not processed into the conclusion consciously. They are inductive surmises from long ordinary experience condensed to a point where the inference made is subconscious. That people dislike being hit comes from observing people's reactions when they are, one's own empathy with the resulting pain, imagining it done to oneself, background knowledge about damage it might cause, etc. Same with people eating dinners, at least once in a while, or background knowledge about the whales and the moon, implied by mere familiarity with what the words mean. When such surmises are reflected upon their origin is colloquially labeled as "common sense".

Peirce thought a lot about what scholastics called logica utens, practical "implicit" logic. I'll quote his opinion on another famously accepted "inconsequential" claim, the one Descartes accepted so much as to believe it the indubitable foundation of all reasoning, upon which he tries to build chains of inferences leading to equally "indubitable" conclusions. It is his cogito, anticipated, to an extent, by Augustine. According to Peirce, "I think, therefore I am" is not an indubitable foundation, certain "in itself", but an instinctive surmise from a multitude of other less abstract ordinary acceptances. It is their intertwining with it, like strands in a cable, which holds it in place as "indubitable":

"There are, however, cases in which we are conscious that a belief has been determined by another given belief, but are not conscious that it proceeds on any general principle. Such is St. Augustine's "cogito, ergo sum." Such a process should be called, not a reasoning, but an acritical inference.

[...] Descartes thought this "très-clair"; but it is a fundamental mistake to suppose that an idea which stands isolated can be otherwise than perfectly blind. He professes to doubt the testimony of his memory; and in that case all that is left is a vague indescribable idea. There is no warrant for putting it into the first person singular. "I think" begs the question. "There is an idea: therefore, I am," it may be contended represents a compulsion of thought; but it is not a rational compulsion.

[...] Philosophy ought to... trust rather to the multitude and variety of its arguments than to the conclusiveness of any one. Its reasoning should not form a chain which is no stronger than its weakest link, but a cable whose fibers may be ever so slender, provided they are sufficiently numerous and intimately connected." [quoted from Collected Papers of C. S. Peirce]

Another philosopher who famously reflected on our countless applications of common sense was Moore. In his Defence of Common Sense he gives many other examples of easily accepted truisms, not necessarily inconsequential, now called Moorean certainties:

"I begin, then, with my list of truisms, every one of which (in my own opinion) I know, with certainty, to be true... There exists at present a living human body, which is my body. This body was born at a certain time in the past, and has existed continuously ever since, though not without undergoing changes; it was, for instance, much smaller when it was born, and for some time afterwards, than it is now. Ever since it was born, it has been either in contact with or not far from the surface of the earth; and, at every moment since it was born, there have also existed many other things, having shape and size in three dimensions...

[...] Among the things which have, in this sense, formed part of its environment (i.e. have been either in contact with it, or at some distance from it, however great) there have, at every moment since its birth, been large numbers of other living human bodies... and many of these bodies have already died and ceased to exist. But the earth had existed also for many years before my body was born; and for many of these years, also, large numbers of human bodies had, at every moment, been alive upon it; and many of these bodies had died and ceased to exist before it was born".

Later he distilled it into a famous "hand argument":""I can prove now, for instance, that two human hands exist. How?. By holding up my two hands, and saying, as I make a certain gesture with the right hand "Here is one hand" and adding, as I make a certain gesture with the left "and here is another."". Wittgenstein was so taken by Moore's musings that he devoted his last work, On Certainty, to them. And he found some of Moore's truisms to be so consequential as to dub them hinge propositions, around which all other empirical reasoning revolves:

"That is to say, the questions that we raise and our doubts depend on the fact that some propositions are exempt from doubt, are as it were like hinges on which those turn.

But it isn't that the situation is like this: We just can't investigate everything, and for that reason we are forced to rest content with assumption. If I want the door to turn, the hinges must stay put." [OC 341,343]

  • This is the right answer. tl;dr: "You don't care." – VSO Feb 19 '20 at 23:31
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    Relevant xkcd: xkcd.com/2129 – Sebastian Lenartowicz Feb 20 '20 at 10:52
  • @SebastianLenartowicz Theorum: There is always at least one relevant XKCD . || The calorie context of the supplies would give some insight into expectations on self sufficiency, and knowing what one does with that much vinegar would be enlightening if not actually life changing. Probably. . – Russell McMahon Feb 20 '20 at 15:46
  • @RussellMcMahon vinegar has always had lots and lots of uses from cleaning to food preparation and preservation. At the time it also took months to produce. If there was a list of required supplies, it isn't surprising vinegar would be on it. It was a staple of life. – Mr.Mindor Feb 20 '20 at 16:15
  • @Mr.Mindor Some yes. I know it has its uses, but .... . It's a byproduct of alcohol production 0 essentially its alcohol that's oxidised. The other material is interesting by dint of its sheer mass. A US bushel is about 34 litres dry mass. So 10 bushels of meal and 4 gallons of liquids. SG rolled oats about 0.36 so meal say 0.4 - 0.5. So 34l x 10 bushels x 0.4 , + liquids = 130 - 150 kg of food/person. || Say 3 cal/g (as not pure dry matter) or about 500,000 kCal or about 1500 kCal/day for a year. Survivable but needs supplementing. ie maybe a years food supplies. (VERY rough) E&OE. – Russell McMahon Feb 20 '20 at 19:39

These are simple conclusions from inductive reasoning.

  1. I don't like it when I hit my thumb with a hammer.
  2. I don't like it when I bit my head on something.
  3. Even though I haven't been hit on the head with a hammer, I can assume it would hurt just as much if not more than the other things I've hit my head on.
  4. From personal experience and pop culture I know other people experience pain.
  5. I can conclude they too would not like to be hit on the head with a hammer.
  1. Donald Trump is a human.
  2. Humans need and enjoy food.
  3. In Western culture it is most common to eat food in the evening most days.
  4. Unless there were extenuating circumstances, Trump probably ate dinner last week.
  1. Whales live in the ocean.
  2. It is difficult and expensive to get to the moon.
  3. When we visited the moon we didn't find oceans, nor did we find any life at all.
  4. It would be prohibitively expensive to set up an aquarium on the moon, and no government or private company has even sent a human there since 1972, so it's reasonable to assume they haven't sent a whale to the moon when a whale would weigh many times a human and require even more weight in water tanks.
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    @MauroALLEGRANZA surely you don't need much of a sample size to assume it will hurt, if every time you've hit your thumb (or other body part) with a hammer (or similar item) it hurt to some extent. And if you do a bit of DIY you've probably done it a few times. Of course you could deem it to be "hit" if it hurt and "tapped" if it didn't, but that's more semantics than anything else – Chris H Feb 19 '20 at 15:59
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    if you are a normal human - I would concur (Hammer-> thumb) a few dozen times ... it just happens, when you aim next to the nail ^^ and Instantly you remember the pain you felt the dozen times before ..Though - I admit changing the way I hold my hand over time .. to avoid hitting thumb or fingers directly - now I hit the part of the hand between thumb and index-finger - and trust me, although the surface area is bigger thus pressure is lower - the pain is there despite that – eagle275 Feb 19 '20 at 16:31
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    You can arrive at the same conclusions with more steps. It's all about the number of assumptions you'll accept and their strength, based on the evidence you have at your disposal. I don't want to try eating bugs: a) I've never eaten a bug. b) some bugs're eaten in other cultures; however: c) I have a negative, visceral reaction to the sight of bugs d) I'm currently satisfied with my current diet e) I'm relatively adventurous when it comes to trying new foods of other varieties. Therefore, while I might like eating bugs, the evidence and assumptions I have make the prospect undesirable. – John Doe Feb 19 '20 at 18:29
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    Furthermore, these are arguments that our brain is able to make subconsciously. OP likely made similar arguments in her head but did not express them explicitly. This is what is known as intuition. – Nacht Feb 19 '20 at 23:04
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    @RonJohn what exactly is manifestly untrue? Personal experience? Pop culture? Learning from them? Are you claiming that empathy is entirely genetic with no learned component? Citations seriously needed. – barbecue Feb 20 '20 at 16:11

Maybe not so much a philosophical / logic-based argument, but in science there is a very helpful principle that most reasonable people (not only scientists) seem to have internalized:

Extraordinary claims require extraordinary evidence.

(or, to flip it around, not much evidence is needed to support a very mundane claim)

This snappy quote is attributed to Carl Sagan, but it's based on an original principle by Pierre-Simon Laplace.

The underlying assumption here is that we often actually already have a good deal of evidence supporting mundane claims. I don't need a scientific study to tell me that hitting my head with a hammer will hurt, because I have run into heavy objects before and it hurt, and I have heard that other people hit their finger with a hammer and it hurt. No evidence points towards hitting specifically my head with a hammer will not hurt, so why would I doubt the veracity of this conclusion?

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    Strictly speaking, to flip it around, claims that do not require extraordinary evidence must not be extraordinary :P – user253751 Feb 19 '20 at 18:56
  • The principle is sometimes misused: Someone hears a claim he/she doesn’t like and tags it extraordinary in order to demand extraordinary evidence. And the opposite: you like the claim, so you assume it’s true with no evidence, and re-post it on social media. – WGroleau Feb 20 '20 at 15:58
  • How do you determine that a claim is extraordinary? – Mike Scott Feb 20 '20 at 21:13
  • @MikeScott It is, at least to an extent, a tautology. It is essentially saying: "Anything that cannot be demonstrated from common experience requires more than common experience to demonstrate." – called2voyage Feb 20 '20 at 21:32

The obvious answer for this is that we don't require specific evidence because we use reason based on a normative understanding of the world. In other words:

  1. "Most people don't like to be hit on the head with a hammer." As a matter of experience, people generally do not like to be hit on any part of their body with any hard object. Simple deduction yields the specific statement.
  2. "Donald Trump ate dinner some time last week." Humans require food for continued survival, and Donald Trump is (ostensibly) human and (ostensibly) alive. Further, while humans can survive for more than a week without food, they generally do so only for specific reasons. Donald Trump is not impoverished, does not seem to be trying to lose weight, and is not given to spiritual or philosophical fasts. Therefore it is reasonable to assume he ate dinner within the last week.
  3. "There has yet to be a whale on the moon." Whales are terrestrial creatures who have not (so far as we know) developed space flight. No human spacecraft has carried a whale to the moon (again, so far as we know), and there would be no obvious purpose to blasting a multi-ton aquatic mammal into an environment in which it could not possibly survive, so therefore it's reasonable to conclude no whales have gotten there.

This is one of the trickier things about scientific reasoning that people often get wrong. Statements of this sort are null hypotheses — statements that reflect a current norm of understanding — and as such do not require proof, evidence, or justification. They simply are, as a kind of sociocultural tautology. Such normative statements are subject to refutation, of course, and that's usually the best response you can give to people who demand evidence on a null. For instance, if someone contradicts the first statement, shrug amiably and suggest that if they want to say that people do like being hit on the head with a hammer, that is a valid empirical claim they should test against the null hypothesis that people do not like it. They should find a randomly selected group of volunteers, buy a hammer, and hit each volunteer on the head with it, recording their responses. After that — and a bit of statistical analysis — they will have evidence that supports or refutes their alternate hypothesis.

Note that I'm not being sarcastic. That is precisely what they should do if they truly want to object to the normative idea that people dislike being hit on the head with hammers. If they are not serious enough to do their due diligence, then the objection they raise is silly and tendentious, and not serious enough to be given any credit.

It takes a decent amount of discrimination to know when you have work to do to defend your argument and when other people have work to do to refute it. Clearly if you are saying something novel you have an obligation build a case for it, and you shouldn't slack on that. But be aware that there are a lot of people who — although otherwise largely incapable of rational thought — are wily enough to cast doubt on what you say simply by raising absurdist objections and demanding evidence for things that are normatively established. Don't fall into the trap.

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    How long can a lizard person survive without food? – user253751 Feb 19 '20 at 18:57

The skeptics would argue that you accept these because you eventually have to. A common argument is the Münchhausen trilemma it is focused on the idea of "proving" statements via rational means, and argues that all rational arguments must eventually end in one of:

  • A circular argument (I know X is true because X is true)
  • A regressive argument (I can prove any X is true by first proving X+1 is true)
  • An axiomatic argument (X is true because it assumed to be so)

We typically frown upon circular arguments and regressive ones in our society. We prefer the axioms. Regardless, the skeptics argue that you will always have to come up to one of these pesky cases eventually.

Once we accept that our rational argument must eventually be founded in one of these, it isn't such a bad thing that we bring one into play. Which axioms we assume (such as whether an individual doesn't like being hit with a hammer) is a pragmatic question. Several of the other answers provide excellent arguments as to why we pick specific axioms.

The other argument I tend to make, which is along similar lines, I that rational thought is not free It consumes resources, and at some point the costs outweigh the benefits. This is a utilitarian argument, of course, but its founded on the skeptical approach which says that no matter how much we spend, we'll never escape these three arguments, so one must approach things pragmatically.

  • Beyond pragmatism and energy conservation, I have tried to justify axioms by arguing that some set of them precede knowledge and logical thought. We evolved from inanimate objects (basic chemistry, etc) and thus there is some connection between the laws of nature and our physical structure through the filter of evolution. The root of knowledge is really a physical correlation between brain-state and environment which hooks us in to reality in a deterministic way. That is also a utilitarian argument in a sense, but it changes the criteria to natural-selection which seems more reliable, somehow. – user3646932 Aug 14 '20 at 8:29

Question: Why do I accept some inconsequential claims as "obviously true" without evidence?

Answer: Because you do not understand your own biases and thought processes and what conclusions they allow you to draw. You should be accepting (at least these three example) inconsequential claims as "most likely true" until you learn of contradictory evidence. But most importantly, you should think before accepting them as such, so you understand why you do it.

Sorry if this seems a bit confrontational, but I want to show you that you've included in your questions three examples of conclusions that are not at all obviously true from the information that a regular person would have access to and the premises they can establish from that information.

I'm taking these assumptions:

  • You are a person capable of drawing conclusions from some premises, and are quite good at it
  • You do not possess significantly more or rarer information than an average, educated person
  • You have biases, from your education, upbringing, environment, etc

Most people don't like to be hit on the head with a hammer.

This seems a logical conclusion from the following premises:

  • Being hit on the head with a hammer causes pain for most people (scientifically provable, we can dig deeper if necessary)
  • Most people don't like pain (not immediately provable, but stick with me)

The problem here is your definition of most. If you consider most = over 50% of the world's people (without nitpicking the definition of people), you must realize that you have no direct, verified information about over 50% of the world's people. You only have information about a small sample, and you're using inference to draw your conclusion. This alone should be an intuitive indicator that you might be wrong (even if the chance seems small), but let's think how wrong you can be.

You see, the small sample of people you know might be a very bad representation of the world's population. Did you know that over 50% of the world's population lives in South and South-East Asia? If you've lived all your life in a western country, your sample is a very bad representation of the world's population, so there's a non-negligible chance that you're wrong in your conclusion.

A better analysis would start from these premises:

  • Being hit on the head with a hammer causes pain for most people (scientifically provable, we can dig deeper if necessary)
  • I have some knowledge of the cultures of over 80% of the world's population (80% is an example, but it's doable)
  • I have never heard of a majority of people in those cultures liking pain

Conclusion: it is most likely that Most people don't like to be hit on the head with a hammer.

Donald Trump ate dinner some time last week.

This one's simpler. Some good premises would be:

  • In the US it is customary to eat dinner every day
  • Donald Trump observes US customs
  • Sometimes, people in the US skip dinner
  • Most of the times people in the US skip dinner it's because of an emergency or other, more important engagements
  • Donald Trump is a very busy person

From there, you can see that it's not that unfathomable that Trump skips dinner every once in a while. Say he skips dinner once every 10 days, so 10% of the time. The chance that he skipped all 5 dinners on the last 5 days is (naively calculated) 0.00001, or 0.001%. Very low, but not 0, so already disproving "obviously true". A non-naive calculation would include the realization that if a busy person skipped dinner on a given day, they're more likely to skip dinner on the following day, for example due to an excess of work that isn't resolved in 24 hours.

In this case, you might think you're very familiar with this person's habits, but they might not behave as similar to yourself as you expect.

Understanding how these claims are "most likely true" instead of "obviously true" actually helps you understand why they are most likely true (at least that's what I'm hoping with this answer). Now, for any other inconsequential claim, you can offer evidence as to why you think it's most likely true, and if you've considered your premises and drawn your conclusions right, you'll be right most of the time.

Once in a while, someone will give you some new information that you hadn't considered (for example, someone could comment on this answer "The US has a constitutional amendment that states the US President cannot skip dinner more than three days in a row"), and you'll have to revisit your premises and draw a new conclusion, which might be different or might be the same.

  • I question whether "Donald Trump is a very busy person" is a good premise... – barbecue Feb 20 '20 at 16:14
  • @barbecue he's busy with twitter, at the very least! jokes aside, you mean it's not true, or not useful/relevant? – Blueriver Feb 20 '20 at 16:50
  • I guess if you consider time spent on social media/tv shows to be "being busy" he could be considered busy. I consider busy to mean busy with useful and productive activities. Lollygagging around a racetrack and responding to mean tweets suggests he has plenty of spare time. – barbecue Feb 20 '20 at 17:01
  • Risk management. The probability of being wrong weighted against the gravity of the consequences of being wrong. Maybe we can comfortably guess with 99.999% certainty that Trump had dinner last week at least once, but if the consequence for us being wrong in that assumption was, say, the destruction of the planet, then we might not be satisfied with that level of certainty and would dig for more evidence to cement our certainty. This applies, I think, to most of the examples. – J... Feb 21 '20 at 18:51

These claims are also fairly inconsequential. If I'm wrong about such claims, it simply doesn't matter.

From an socio-economic point of view, one reason is Opportunity Cost.

You only have so much time in the day. If you spend time vetting whether or not [checks notes] "ponies aren't baby horses" you're not doing something else more important with that time.

What you deem consequential or not is often influenced by biases and beliefs, needs and wants. One is more inclined to accept as true, or at least not examine too thoroughly, statements which agree with them. We see this used to great effect in propaganda and marketing and con artists.

Your political beliefs will affect how you examine "immigrants are stealing our jobs". If you have a cold that will influence your reading of "NuSneeze will ease your cold symptoms". If you want to make money quick an offer like "give me $10 and I'll give you $50 next week" may get less examination.

When you invert the claim sometimes it remains inconsequential. "Donald Trump did not eat dinner last week". The president's a busy guy, I can easily see reasons for him not having time for dinner for a whole week.

But sometimes its consequences can change dramatically because of how much of your world view has to be wrong for it to be true. "There has been a whale on the moon" envisions an entire secret space program to launch a huge sea mammal to the moon. How?! Why?! What?! Or maybe whales came from space?! This is, in part, why scientists are so concerned with seemingly inconsequential observations; all observations must fit into a coherent model of reality.

"Most people like to be hit on the head with a hammer". I assure you I am not most people. Why do you have a hammer? Stop looking at me like that.


Because the semantic content of these claims is so simple and straightforward that you extrapolate from your personal experience and general knowledge of the world without even noticing that you do so.

The fact that you judge these claims as inconsequential may be misleading. Instead of Donald Trump, you could make the 2nd sentence about your mother or another person near to you, and would almost certainly likewise accept it as true even though it would have consequences you care about if it were false.

(obviously, if that person has a known condition related to food, things change.)

Our brains are interesting things and consciousness twice so. Dennett among philosophers, or any textbook on psychology teach us that it isn't as simple as we think and a lot of thinking is done for us, not by us. Specifically, the parts of your brain tasked with language processing will parse those sentences, and to understand the meaning dig into your memory sections to pull out whatever related concepts are required to make sense of the words. Without even trying they will get the context of, for example, in the 3rd case the Moon Landing, maybe even the date and the name "Armstrong". They will fail to find any connection between "moon" and "whale" and thus the fact that these two things are not related has been activated in your brain. This activation is what makes the negation appear trivially true.

Psychologists would say that your System One is processing the data and giving you an answer from heuristics and simple extrapolation, long before your consciousness is even engaged.

The difference to other statements is that something like "Ammonium Dichromate is bad for your health if swallowed in quantities larger than about one tea spoon." do not appear trivially true or false is that they require much more processing and thus activate the slow System Two, because no trivial connection can be found and you need to dig deeper into what chemical that is and why the tea spoon size may be important or maybe it's a red herring?

(Kahneman describes System One and Two well in his "Thinking, Fast and Slow" book).

Immediate assessment of simple statements and instinctive assignment of truth values is a survival trait and has thus evolved in us humans, because sometimes you need to make a decision right now or something will kill you - but at the same time you can't all day ponder trivially near-impossible possibilities, that would take up too much important processing power.


Note that you probably also accept many extremely consequential (on a personal or general level) claims as true without empirical evidence. Therefore the relevant property of your claims is not that their truth or falseness is inconsequential — that only determines whether we bother to ponder them at all (and unless we perform a philosophical exercise, we typically don't.)

The relevant property making us accept them without further evidence until we have convincing falsification is that they fit well with other claims we have come to regard as true. This is the general principle behind the specific ways mentioned by others. As an example we suppose that others feel like we do, or we perform inductive reasoning. The technical term is coherence. It's a bit like a public key infrastructure.

Carl Sagan's aphorism is actually a popular way to express the need for coherence, if you consider that "extraordinary" means "does not fit well with the rest of what I think is true".

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