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The appeal to common sense – garbage in the guise of gumption

February 6, 2014
It goes without saying that this tactic is a red flag.

How to recognise this tactic

The perpetrator tries to persuade you to accept or reject a claim based on what’s supposedly “common sense”. Look out for key words such as “Obviously, …”, “Naturally, …”, “Everyone knows …” or “It goes without saying that …”.

There is always a well-known solution to every human problem — neat, plausible, and wrong.

H L Mencken, American writer, 1917


How this tactic is supposed to work

This tactic depends on the notion that common sense is the basis of all correct reasoning. Users may even insist that science is really just common sense at heart.  After all, back in 1854, T H Huxley said:

Science is, I believe, nothing but trained and organised common sense, differing from the latter only as a veteran may differ from the raw recruit.

Their line of argument is that if some complex scientific procedure comes out with conclusions that “defy common sense”, then the science must be wrong.

Why do people use this tactic?

People use this tactic when they don’t accept a scientific conclusion and want you to adopt their position. They either don’t understand the science, don’t want to understand it, or can’t muster good reasons for not accepting it. They promote the common sense explanation as temptingly simple, straightforward and authoritative. They try to distract you from delving deeper into the science by priming you to ignore it.

What’s wrong with this tactic

Basic common sense is often wrong. It tells you that the earth is flat, that heavy things fall faster than light ones, that the sun rotates around the earth, that you should throw water on an oil fire and that stress causes hypertension. Science tells us that all of those conclusions are wrong. Common sense doesn’t predict that you can melt ice by throwing salt onto it, that you can get sunburned on an overcast day or that two brown-eyed parents can have a blue-eyed child. Science can explain all those things. Huxley’s idea that science is highly refined common sense has a lot of support. But the “highly refined” part is very important. Physicist John Ziman puts it this way:

… it is in its conformity to the small print of common sense that science is distinctive. … Taken one by one, the cognitive norms that have to be satisfied – accuracy, specificity, reproducibility, generality, coherence, consistency, rigour, and so on – are all perfectly commonsensical: but they are seldom applied simultaneously outside science.

And philosopher Susan Haack expresses it like this:

… inquiry in the sciences is like empirical inquiry of the most ordinary, everyday kind – only conducted with greater care, detail, precision, and persistence, and often by many people within and across generations … … the evidence with respect to scientific claims and theories is like the evidence with respect to the most ordinary, everyday claims about the world – only denser, more complex, and almost always a pooled resource.

Common sense is often fine in very simple situations where there are few factors involved, and relationships between the factors are linear. (Does the amount of sugar I put in my coffee influence the sweetness?). When things get complex, (Will I get dehydrated from drinking coffee?), science is the way to go. When science and common sense seem to disagree, it’s a pretty safe bet that the science has it right.

What to do when confronted by this tactic

The perpetrator is hoping you’ll automatically defer to the common sense argument. Don’t. Be curious. Demand evidence. Ask if the scientific view differs from the common sense view. If it does, try to find out why scientists are confident in their conclusions despite the apparent contradiction. It’s always possible that the science is wrong, but you can only say that after critically examining the scientific argument. Don’t accept the excuse that scientists are scheming to cover up the truth, and look for red flags such as rooster syndrome, cherry-picking and apophenia.

Variations and related tactics

The appeal to common sense is similar to the appeal to common belief or bandwagon fallacy (for example, that antibiotics will cure a cold). The appeal to common belief is a little less persuasive because common sense implies some logical validity, while it is well know that many common beliefs are wrong.


Further reading

Crafty contrarians and wily watchdogs – donning the mantle of shrewdness

Scientific knowledge suppresses but does not supplant earlier intuitions by Andrew Shtulman  and Joshua Valcarcel in Cognition.

Why scientific truth may hurt by Adam Rutherford at The Guardian.

We can’t trust common sense but we can trust science by Peter Ellerton at The Conversation.

You can add to the list of examples by leaving a comment.

H L Mencken’s quote is from “The Divine Afflatus” in New York Evening Mail (16 November 1917). Greg Williams’ Buttered Cat cartoon is from WikiMedia Commons. T H Huxley’s quote is from “On the Educational Value of the Natural History Sciences” (1854). John Ziman’s quote is from Real Science: What it is, and what it means, Prometheus Books, New York, p 314 Susan Haack’s quote is from Defending Science – within reason, Prometheus Books, New York, p iv The Global Temperature and Carbon Dioxide graph is from NCDC. The creationist question photo by is Matt Stopera from BuzzFeed

This is one of ScienceOrNot’s Science red flags. See them all here.
  1. Hi Graham,
    I really like how you are consistently educating for attitudinal change (the hardest of all…)

  2. David permalink

    It seems to me that understanding that “common sense” is often wrong is the first step on the path to critical thinking. If you look at hatred of science, whether it’s on the right (global warming deniers), or on the left (hatred of GMO), both of them are deeply rooted in “common sense”. “Common sense tells you man can’t change the weather”. “Common sense tells you GMO is poison”.

  3. David permalink

    BTW, your article is excellent, and I think everyone that teaches science and wants to enhance the understanding of science would do well to give more attention to this subject. I also think it’s a subject that the average person can get their head around easier than confirmation bias. But if people can be taught not to trust their “common sense”, the result is less confirmation bias.

  4. “If we came from monkeys why are there still monkeys?”

    Thunderf00t has an excellent answer to that one. If a creationist ever uses it, ask them the question back “If Americans came from Europeans then why are there still Europeans?”

  5. So true!! This is a favourite anti-vax technique too – the point of lists of scary-sounding ingredients is that it’s so-called “common sense” that scary sounding things must be bad, and their entire meme-cluster about “injecting neurotoxins” being obviously bad for people rests on the same premise.

  6. Colin permalink

    Agree with the ‘Common sense” fallacy, but I do wonder about how far the people on “Skeptical Science” want to stretch (or, rather, torture) an analogy:

    “The Earth is insignificant, it’s only 3 ppm of the mass of the solar system…”

    Well – in cosmological terms – the earth IS insignificant. From a SUBJECTIVE viewpoint (i.e. Ours) it is significant. But Science isn’t about subjectivity, is it? And the whole arsenic deadly poison compared to CO2 – therefore implying it , too, is a deadly poison, smacks of sensationalism.

    We need to take the fight up to the deniers, but not at the risk of being accused of comparing apples with oranges, subjectivity, subectivity, or gross misrepresentation.

    • You may have a point with the Earth comparison, Colin, but I can’t agree with your take on the arsenic. I don’t think there’s any implication that CO2 is poisonous. As the following sentence says, “Small amounts of very active substances can cause large effects.”. When you’re using analogy, it’s always the case that certain parts correspond and others don’t. In this case, it’s the magnitude of the effects that are similar, but we’re talking about chemical effects for arsenic and physical effects for CO2.

      • Colin permalink

        Well, I’m still not completely convinced that there isn’t – even, perhaps, subliminally – an idea that to get the point across about the imminent danger of CO2 becoming a rampant force in AGW, that it must be made through analogies that emphasise or hint at that danger.

        After all, if proponents of AGW compared the impact of CO2 with, say, ‘trace’ elements of vitamins in the body or via a comparison of CO2 vs N and O2 as proportions of gumballs in a vending machine or some other innocuous measure, it would hardly be controversial or provocative enough to garner the desired response, would it?

        All I am saying is that we need to be careful not to be guilty of precisely the same overblown verbiage and hyperbole that we accuse the deniers of; we must stick completely to facts and be completely objective. Which is what Science is supposed to be about, anyway, isn’t it?

        Frankly, I’d much rather be guilty of not convincing a layperson about AGW because I couched the argument purely in facts, than be accused of ‘gilding the lily’ just to win them over in the way the deniers do.

        • I appreciate your point Colin. However, one of the best ways of debunking the common sense fallacy is to give an example where the claim obviously doesn’t apply. In many cases, the person putting up the argument isn’t able to follow the subtleties of the scientific argument, but may be convinced by an analogy that shows their common sense argument doesn’t hold water. My feeling is that a genuine AGW skeptic will accept the distinction (viz that we’re attacking the fallacy, not trying to say that CO2 is a poison). A straight out denier will probably try to confuse the issue, but what’s new?

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