People would find normal to plainly use reason in a lot of situations such as at work, designing a marketing project, writing a scientific article, drafting an architectural plan for a house, or in private, such as preparing a shopping list, planning their holidays. Politicians and CEOs are expected to act and decide rationally. In this case, by using reason, they think and rethink, edit, extend, cut, reorganize their judgments and decisions (sometimes at first stemming from intuition and emotions), looping from taking a global perspective on the situation, then focusing on details; and this many times.

Meanwhile, for other things, sometimes people believe that reason is unhelpful, even detrimental; for example when making friends, dating boyfriends or girlfriends, judging the action of other people, or the veracity of outlet news, speaking up in public, arguing with subways travellers, relying mostly on intuition or emotion, without much cognitive analysis/processing of their intuition and emotion.

The situations in the second paragraph are more inter-relational, and so people may say "emotions help to make (authentic) connections". Yes, and indeed empathy is made in part of being able to feel the other person's feelings (psychopath, in particular so-called "primary psychopaths", are emotionally deficient). But on the other hand, only reason help to take the view of the other person or party, and therefore not be selfish, socially awkward, or inappropriate, in these inter-relational settings.

Why should reason be used some times but not others?

(The same question would be applied to figures of intellectual and cultural movements who ambiguously disregard reason such as postmodernism, or romanticism, but who still obviously use it when they write their books and poems).

P.s.: As alluded in my question, I don't discard or ignore emotions and intuition (neither any Enlightnement thinkers ever did, AFAIK, even Spinoza and Descartes wrote entire books investigating emotions), just saying that emotions and intuition when used blindly without the recourse of proper cognitive scanning can be harmful.

  • @RodolfoAP I would say the contrary, emotions are always used, reason is not
    – Starckman
    Commented Apr 5, 2023 at 9:33
  • Look up 'cognitive ease' and the 'illusory truth effect', which describe powerful psychological mechanisms, one or both of which are often in play when "making friends, dating boyfriends or girlfriends, judging the action of other people, or the veracity of outlet news, speaking up in public, arguing with subways travellers" and at other times when we have an interest in believing things that is more powerful than our desire for accurate conclusions. Commented Apr 5, 2023 at 9:35
  • Cognitive Ease. Illusory Truth Effect. Commented Apr 5, 2023 at 9:43
  • 1
    Sorry, typo. When emotions differ from reason, it means that reason, which is based on logic, is not able to be logically consistent with instinct, which applies a different type of logic: that based on body signals of survival. No one is better than the other, surviving implies logical consistency between both. If both are consistent, individuals tend to survive. If both are not consistent, individuals tends to harm himself, and even risk death. For example, a lot of people are rational communists and emotional capitalists, and such inconsistency usually leads to poverty.
    – RodolfoAP
    Commented Apr 5, 2023 at 9:44
  • First, people do not decide when to use reason by using reason. It is not necessarily that it shouldn't be used when it isn't, it is just that it isn't. And second, reason can only be used when it has something to work with, factual and normative premises. In situations where norms are muddled and/or facts are obscure it may well be best to rely on habits, emotions and intuition than to have reason work garbage in, garbage out. "A little knowledge is a dangerous thing", as Pope is misquoted to say, the story of "scientific communism" is a historical illustration.
    – Conifold
    Commented Apr 5, 2023 at 10:24

4 Answers 4


I suggest there are a handful of practical considerations here.

Human instincts have evolved over millennia to be a useful tool for making rapid assessments, so if you need to make a quick decision- or one with with a low-stakes outcome- go with your instinct.

Many decisions have no basis in reason- do I want to listen to Beethoven now or Elvis? Such questions are purely a matter of personal preference.

There are countless circumstances in which human instincts and emotions are not capable of reaching a sensible conclusion. For example, designing a silicon chip, determining the effectiveness of a vaccine, etc etc. For those, reasoning is essential.

  • "so if you need to make a quick decision- or one with with a low-stakes outcome- go with your instinct." Sometimes there also be some laziness at stake right? Processing emotions and intuitions can be deleting
    – Starckman
    Commented Apr 5, 2023 at 9:01
  • Isn't deciding to listen to Beethoven or Elvis actually a very simple example of reason at play? Don't you decide because of the desire to do one more than the other? Ie: 'I want to listen to Elvis, therefore I will listen to Elvis. Commented Apr 5, 2023 at 9:39
  • 1
    @Futilitarian I think you can do that if you wish, but you will obscure rather than illuminate by drawing a veil of contrived reason over everything. I find the smell of roses creates a certain sensation in my mind therefore I will find it pleasant. I have an irrational fear of heights therefore I won't go near that drop. The striking of my knee by a doctor with a hammer has caused a certain reaction in my leg therefore I will jerk it. Everything can be made an example of reason at play in that sense. It is meaningless. Commented Apr 5, 2023 at 9:47
  • Isn't identifying the fact that there is a difference between desire and decision meaningful? Surely avoiding such a conflation is not meaningless. I'm no expert, but my limited experience suggests philosophers have gone to some trouble to investigate the nuances of will vs decision etc. Finding the smell of roses pleasant is not rational, but then choosing to buy some because of that smell is rational. The irrational fear of heights does not take away from the fact that to avoid heights because of the fear of falling is rational. The hammer on knee is reflex, and hence non rational. Commented Apr 5, 2023 at 9:52
  • I guess what I'm getting at is your comment, 'Many decisions have no basis in reason'. I find that interesting and would sincerely like to know more, because it's not something I've though about a great deal and I'm struggling to think of decisions we make that aren't made for a reason. Unless perhaps we're talking about deterministic/random situations or perhaps some kind of mental illness? Commented Apr 5, 2023 at 9:54

We could start with e.g. Kant's Critique of Pure Reason to have a well-known historical reference:


his most influential contribution to metaphysics: the abandonment of the quest to try to know the world as it is "in itself" independent of sense experience.

Then we could modernize our notions by cognitive biases:


In essence, it's not enough to trust reason alone, but reason within some constraints that we learn in relation to the environment.


You should actively not use reason in situations where your ability to reliably reason about the accuracy of your reasoning is known to be deficient.

Our ability to use reason to make a convincing case (to ourselves or others) is insanely higher than our ability to actually make a correct case.

In some areas, we have sufficiently simplified the world (or developed tools that handle the complexity) that reason is a great tool to interact with it.

Look at the cases you judge as being reasonable to use reason:

  • designing a marketing project
  • writing a scientific article
  • drafting an architectural plan for a house
  • preparing a shopping list
  • planning their holidays

Designing a marketing project, we have entire fields of expertise and social systems -- economies -- designed around making the selling of goods and marketing them as easy as we can.

For scientific articles, the goal of science has been to develop a way to reason about the world. Problems that are not suitable to reason about, or that you haven't succeeded in working out how to reason about, aren't good scientific articles; they won't be useful to the consumers of the article.

Engineering and Architecture is also a huge tower human effort into making things simple and effective. We have building codes and patterns and materials and designs that are insanely easier to reason about than the general problem of "I want shelter that is good". You can know the material properties of a steel beam before you even start building your house.

Shopping lists rely on an economy that produces many copies of the same kind of good and stores them in an easy to find and consistent spot for a predictable amount of economic purchasing points. Again, a huge amount of effort, the collective work of billions of humans over 100s of thousands of years, making the problem really really simple.

Even modern holidays rely on huge amounts of tech, from calendars to transportation networks and stable currencies and the like.

Every one of your examples has a tower of human civilization's efforts making the problem amenable to reason. Next to none of them have huge incentives on the other side making people want to avoid making it amenable.

Now, look at your second list:

  • making friends
  • dating boyfriends or girlfriends
  • judging the action of other people
  • the veracity of outlet news
  • speaking up in public
  • arguing with subways travellers

For a bunch of these this is matters of interpersonal trust. Trust is a war; if I can figure out how to make an arbitrary person Trust me using simple and cheap techniques, I can cause nearly unlimited harm to them and use that Trust to take resources from them.

We have structured society in such a way that Trust is insanely easier than it would be without society. We have signifiers of status and identity and community that can be used to make certain kinds of Trust-attacks less likely or more expensive, we have state monopoly on force attempting to make it less dangerous, etc.

But the incentive to exploit Trust means that people are working out ways around the system with lots of incentive. So we can't rely on reason, because we have failed to simplify the system, because people have incentives to keep it from being reliable and easy.

News -- politics -- is a similar Trust game.

The remaining bits looks like social mores and acceptable behavior in public. Here you are mainly signalling you understand the rules of society and abide by them; the actual communication doesn't seem very relevant.

And even the earlier ones - the ones where we have simplified things - remain a battle. Marketing can be viewed as a war to sell useless stuff to marks, scientific articles have to convince reviewers and readers that you should have academic social standing, houses have to look high quality to sell to buyers and advertise their social status, people selling goods would love to sell you worthless stuff for high prices, and the like.

In many cases, we end up with regulation. Grocery stores can't sell rotten food, you can't build a house breaking code, etc. These again attempt to simplify the transaction, and make reason more effective and easier.

In short, humans are great at reason in situations we make reason easy to do. In more complex situations, humans are often overconfident at their ability to reason; they have been trained on the easy situations where reason works well, and project it into harder domains. In those harder domains, using the same reasoning techniques that work fine in the simple domains results in rather poor results.


Whether something is a fallacy in informal arguments depends.

Equivocation, post hoc ergo propter hoc, non sequitor and hasty generalization are commonly classified as forms of argument that are inherently mistaken. In contrast, traditional fallacies like ad hominem, two wrongs reasoning, guilt by association, and appeal to pity are patterns of reasoning which can, when they are constructed in the right way, play a legitimate role within real life reasoning (and are, in view of this, sometimes treated as argument schemes rather than fallacies).


The example of appeal to emotion and dating is a very good example of why. Asserting that all reasoning has to fit the same neo-classical schema is itself poor reasoning, and probably a hasty generalisation.

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