"I spat in my pasta while cooking it, it turned out good, therefore spitting in my pasta is beneficial to the result."

What is the name for such fallacious reasoning?

It seems like A happened before B, and someone deduced A contributed to B.

  • 16
    Post hoc ergo propter hoc. Dec 2, 2019 at 12:07
  • @MauroALLEGRANZA that's it, thanks!
    – effeffe
    Dec 2, 2019 at 12:28
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    – J D
    Dec 2, 2019 at 16:47

4 Answers 4


This kind of reasoning is not necessarily fallacious, at least if framed a little more cautiously, e.g.:

"I spat in my pasta while cooking it last time, it turned out good, and for all I know spitting in it was essential to it tasting good, so I'm going to spit in it again this time, just because I really want it to taste good again this time."

Nevertheless, there are several distinct though related reasons why we might consider the reasoning fallacious -- which also helps to clarify when it is perhaps not fallacious, when the conditions for those reasons don't hold.

(1) Strong prior reasons to not believe the hypothesis. Given our prior broader knowledge about, and theory of, how the world works, we have strong reasons to believe that spitting in the pasta will not make it turn out better, even before ever attempting to cook pasta. Even a little bit of evidence, such as a few prior occasions where spitting in the pasta seemed to correlate with it turning out well, should not outweigh this prior belief. People who let such correlations outweigh strong prior beliefs about how the world works are often labeled superstitious ("It helps my sports team if I wear this shirt."). ... but, if you are, say, a cooking robot that nobody told anything about how the world works, then perhaps it's a reasonable inference.

(2) Overly complex hypothesis (overfitting / no feature selection). Once we start taking into account whether spitting in the pasta helps, we might as well take all kinds of other things into account -- what time of day it is, whether it is sunny outside, etc. When taking so many things into account, it is not surprising that some of them are going to correlate perfectly with the results of a few trials, just by fluke. Ideally we consider only things that we have prior reasons to believe are relevant (see 1). ... but, if there aren't that many things that vary in the environment, and we don't have prior reasons to exclude spitting in the pasta as something likely to be relevant, then maybe it is reasonable.

(3) Being too quick to jump to conclusions / too unwilling to experiment (closely related to the more cautious rephrasing above). Just that we spat in the pasta once and it turned out good is not a whole lot of evidence. To be confident (especially in the face of strong prior reasons to not believe in the effect, see 1) we really should experiment much more, trying it many more times, sometimes spitting, sometimes not (especially if we're considering many hypotheses -- see 2). ... but, if there is no more time left for experimenting and it is crucial that this next pasta turns out right (big date!) and nothing else in the world matters, then maybe it is reasonable.

So, in general, the type of reasoning is not necessarily fallacious; at some level we do it all the time (reinforcement learning -- we look at which actions we take and how good the results turn out to be). But there are certain things that one has to be careful about when doing such reasoning.

  • 3
    Well, just making the hypothesis that spitting may have helped is logically sound (we don't know it didn't help either). However, even without previous knowledge about spitting, asserting it was beneficial still seems wrong to me.
    – effeffe
    Dec 2, 2019 at 16:43
  • @effeffe right, but of course in reality there are all kinds of shades of gray between "it is beneficial" and "for all I know it's beneficial" (for example, "I'm starting to strongly suspect it's beneficial"). I'd say the ultimate question / test in the end is whether you'd act on the hypothesis (spit in the pasta again when you care about the outcome), so maybe that's the best way to interpret my answer -- should I spit on the pasta again? Of course, that's but one interpretation; one might also be inherently interested in how much confidence one has in the hypothesis.
    – present
    Dec 2, 2019 at 18:34

I'd just add a footnote to indicate without any disagreement with present's answer a different way of taking: 'I did it this way, it worked, so what I did is correct'. In the example used, that of spitting, it's assumed that spitting into the pasta while cooking it in some way improved the process of cooking or contributed essentially to the flavour or whatever of the result. The clear implication is that spitting was actually irrelevant. Because the satisfying state of the pizza (X) followed the spitting (Y), therefore Y caused or part-caused X: fallacious, indeed. Post hoc, &c.

I realise this reconstrues the initial statement 'I did it this way, it worked, so what I did is correct' - even if 'this way' (Y), whatever it is, really did work and contribute causally to the process or the result (X), but it would not follow that Y was the correct thing to do. It may have been causally efficacious but only (i.) accidentally so or it may have been causally efficacious but (ii.) inefficient and wasteful of effort or resources and in these senses not have been correct at all. This would typically apply in cases where there is a recognised and reliable technique, correct use of which has not been made.

To repeat, I naturally accept the answer above, but the initial statement can be reconstrued and critiqued as incorrect in terms of means/ end rationality as well. Then the conclusion, 'so what I did is correct', does not follow from the premises by either or both of two norms of rationality, (i.) & (ii.).


The fallacies: "Correlation does not imply causation" + "anecdotal evidence" + "Single Cause fallacy".

The two events are related to the pasta. Experience would indicate this was not the cause, but logically they could be related. Perhaps the sauce would have been too dry. So it's more about the lack of information and jumping to a conclusion (which in this case is likely wrong).

In this case, an extra observation (prior to spitting) would have ruled out the conclusion.


It does not sound as a problem of logic per se.

Let us put it this way: the real world obeys to the laws of the real world, not to the laws of human logical reasoning. There is no way to find out whether spitting in the pasta works with abstract reasoning alone. Humans use observation (and logical reasoning) to try and figure out what the real world might looks like.

So the spitting problem is one of experimentation. There is no absolute certainty there; the best way to prove something in physics, is to work hard to find counter-examples, and fail a sufficient number of times to find any.

So to be "sure" of that spitting in the basta is beneficial, the person would have to repeat the experiment several times with the spitting, to see whether the result is consistently good. But at that point, the person does not know yet how the spitting contributes. For all they know, it could be important, or it would not matter at all.

So the person would have to do the experiment without spitting a number of times, all other things being equal. Do they fail consistently to get better pasta quality than with the spitting? Or is it the same? Or does it start varying wildly (in which case the spitting would perhaps act as a stabilizer)? etc.

Also, the real world is often different, and far more weird and complicated, than what we may have guessed with abstract reasoning.

For an explanation of the difference mathematics and physics, see e.g. the explanation by Richard Feynman.

  • Somebody care to explain what fault they find with this answer? Or did it violate somebody's dogma of "the essence of the universe is all logic"?
    – fralau
    Dec 6, 2019 at 15:00

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