A common argument in today's news is that:

  1. Someone commits a heinous crime by shooting a bunch of people.
  2. Anyone who commits a heinous crime must be insane.
  3. Sane people cannot apply rational thought to explain what motivates the insane.
  4. Therefore, one cannot ascribe a cause or catalyst to a heinous crime.

Is there a fallacy in this logic? If so, what is it?

  • 15
    If 3 is true, the whole of clinical psychology would be doomed. It is like saying humans cannot apply human thought to explain what motivates nonhumans. Or that the thinking cannot apply thought to explain the behavior of inanimate matter. We can observe.
    – user9166
    Dec 1, 2015 at 18:13
  • 6
    Also, if 2 is true then the whole of clinical psychology is doomed, for it has no way to differentiate between crazy and evil. The two are not synonymous, popular Hollywood depictions notwithstanding. Dec 1, 2015 at 18:55
  • 2
    I don't know why it bothers me, but your point 1 shooting is a heinous crime, is not relevant to your conclusion of 4, which utilizes only point 2 and point 3.
    – dsollen
    Dec 1, 2015 at 20:14
  • 1
    @dsollen I think 1 interacts with 2 informally by qualifying what is meant by "heinous crime." Perhaps what is bothersome is that it is only informally linked to the argument but has a side effect of tying the question to a very politically charged current event. When I look at how 1 interacts with 2, 3, and 4, it seems like its intent is to sway the logical argument with external details which, in a perfect world, would not apply to the argument at all.
    – Cort Ammon
    Dec 1, 2015 at 22:05
  • 4
    There is no logic in this fallacy. 2 is clearly false. 3 is clearly false. You cannot draw a valid conclusion from two invalid propositions.
    – Trevel
    Dec 2, 2015 at 18:02

10 Answers 10


The second premise is false unless "heinous crime" and "insane" are defined to make it true by definition, in which case the definitions are question begging. But because people committing heinous crimes are convicted despite the insanity defense, premise 2 fails at least on the legal definition of "insanity".

The third premise is also false; otherwise clinical psychiatrists are either insane or engaged in a futile endeavor.

This would make the argument unsound, but not a fallacy since a fallacy is supposed to derive an erroneous conclusion even if a fallacy's premises are granted.

But there is still a genuine fallacy in this argument because of the substitution of cause for motivation in the conclusion. Even if a maniac is so insane as to be impenetrable even to a most insightful psychiatrist, the maniac's behavior can still be analyzed rationally, by treating the maniac as a black box. It doesn't take understanding of motivations to surmise that poking one with a sharp stick would provoke an outburst, in which case poking would be the cause no matter how convoluted the motivation that mediates between that and the outburst.

Finally, even without the substitution the core of the intended reasoning seems to be that "sane people just can not understand what motivates the insane". This is They're Not Like Us type of ad hominem fallacy, and involves equivocation on "understand". It is also related to what Pasnau calls the content fallacy, the content of mind is conflated with the state of mind to conclude that only insane minds can grasp their likes. We can understand arguments (externally) without sharing their premises or logic but adopting them for the sake, but we can not 'understand' them (internally) since that would involve the sharing. The same goes for the workings of insane mind, even if we can not share them we may still be able to explain them rationally by external reasoning.

  • 1
    nitpick on your terminology, from a logician not a philosopher. while I agree 2 is a large leap in logic I disagree that 2 must be a tautology to be true. He is saying that if criminal then insane, or C -> I. If C and I are true then the statement is true. If C is false and I is true (maybe non criminals are all insane too!?) then it's false. Since there is a satisfiable negation then C -> I is not a tautology, even if it is satisfiable. That he is interested in only the satisfiable case of C & I being true doesn't change the fact that a satisfiable negation exists
    – dsollen
    Dec 1, 2015 at 20:11
  • @dsollen I agree, calling something like "if bachelor then a man" tautologically true is using it loosely, I guess the technical term would be analytically true, but it doesn't sound right colloquially. I rephrased it though.
    – Conifold
    Dec 1, 2015 at 22:13
  • 1
    I agree with your reasoning, although I believe there is something you haven't covered, which can explain how one person may be applying the most absolutly correct logic, and still be deemed illogical. It's when you have false premises. For example, in a twisted kind of way, Saw is a great basis for this. You have 2 guys in a room, with a dead body. An entity then tricks them into doing several actions despite the key that can free is already lost. According to their premises, they were doing everything right. X key exists and can free them. If they do Y they get the key, therefore, Y = free)
    – Oak
    Dec 3, 2015 at 20:31
  • 1
    When in truth, the key is lost, and therefore one of the premises is false, and thus, they are merely torturing eachother, essentially being insane, due to assuming a false premise as true.
    – Oak
    Dec 3, 2015 at 20:32
  • @Conifold "self-evident" or "axiomatically true"
    – MmmHmm
    Mar 12, 2017 at 21:36

I think the fallacy is something along the lines of:

Because we cannot provably apply rational thought to what motivates every insane person, every time, we can never apply rational thought to the insane in any situation.

It also presumes that an explanation one's actions has to be necessary and sufficient, rather than merely a way to convey information.

There's also plenty of arguments that you cannot always apply rational thought to the actions of the sane, but that's another beast.

EDIT: It is, however, an effective way of distancing ones self from the actions of another. It attempts to make the claim "normal people can't possibly ever think this way," reinforcing any desire the speaker has to convince themselves that they are better than that, and would never do such a thing.


There are multiple problems with these statements.

First, insane is not a boolean state. Sanity is a spectrum.

Second, I don't know of anything that says that everyone who commits a heinous crime is insane (even by this very liberal application of the term). There are many heinous crimes committed where the criminals are not insane. Gang murders, rapes, hate crimes, etc.

That aside, I don't think it follows that sane people cannot study insane people. Adults can study children. Humans can study animals. Just because we don't currently have all the models necessary to accurately predict every behavior of the insane does not mean that we can never do so. We simply lack the resources necessary to provide every person with a complete sanity profile, dig into root cause analysis, and apply the appropriate safeguards. In fact, we have multiple protections in place to keep that data out of government hands so it isn't abused.

And the last statement is blatantly and demonstrably false. Many heinous crimes have known motivations. Timothy McVeigh published a letter explaining why he bombed the Oklahoma City Federal Building. Osama Bin Laden published his reasons for orchestrating the 9-11 attacks. I can't imagine a definition of heinous where those crimes are not considered such.

  • 2
    Many people who are regarded as insane have well-thought-out logical reasons for the things they do. My aunt's neighbour's nephew saw the devil looking out of her eyes and the voices told him to kill her. He found this quite reasonable. If you believe in devils and hear voices then it probably is.
    – RedSonja
    Dec 3, 2015 at 13:18

I believe that would just be petitio principii, mistranslated as "begging the question." And doing it twice.

First, you assume the insanity after the fact, based on the evidence of the act, which is defined as insane. Likewise for conflation of "insane" and "inexplicable."

But I am not good at naming fallacies, so there may be a more precise attribution. I'm sure someone can provide. And worth doing. You rightly point out an annoying political response to violent acts. People are only officially "mentally ill" after the act... yet the "solution" becomes preventative measures against "the mentally ill." Bit of "red herring," and closing the legal barn door "after the horses are out."

I might add that Foucault and Derrida had a long debate about the possibility of "reasoning" one's way into "logic" of the "insane." Derrida thought it impossible by definition, I believe. Sorry can't recall reference.


I will take your question, and answer in-line where I can:

A common argument in today's news is that:

1 Someone commits a heinous crime by shooting a bunch of people.

  • Only possibly heinous, as it stands it could be a heinous act or an act of compassion, good, necessary evil depending on context and subject

2 Anyone who commits a heinous crime must be insane.

  • Again not necessarily: motivation and rationale would determine insanity

3 Sane people cannot apply rational thought to explain what motivates the insane.

  • Also not necessarily correct: a sane person could apply a rationale which worked to explain the motivations of an insane person at a given moment or for a given action, that however does not mean that the same motivation would stand for all actions.

4 Therefore, one cannot ascribe a cause or catalyst to a heinous crime.

  • Again not necessarily correct: if the so-called heinous crime were committed for valid (or even invalid) reasons, there may well be a clear catalyst or cause; whether that clear catalyst or cause is valid or justified would be a separate matter, but it could definitely be clear.

Is there a fallacy in this logic? If so what is it?

Heinous: this word can mean hateful, odious, abominable, totally reprehensible, utterly wicked. None of these necessarily infer that they are random, insensate, irrational or non-cognisant acts.

Insane: this can mean in a state of mind which prevents normal perception, behaviour, or social interaction; seriously mentally ill; possessed of divergent reason and logical processes.

However both these terms are sociologically and societally weighted, and are defined in relation to socially accepted norms, and hence highly subjective and variable by location, era, etc..

The fallacy is innate to the style and is based on the presumptive and assumptive nature of presentation; the language of news and media is primarily driven by sensationalism (some further evidence/reading in regards of media sensationalism:1,2,3,4,5) and propagandism: made overly dramatic and emotive and presented as absolute truism, with little or no presentation of alternative possibilities put in place, unless they aid the sensationalism or propagandism.

As with any communication one should strive to understand the meaning and motivation behind it as well as intended aims, that will lead to a better understanding of what is being communicated as well as how it is being communicated.


Insane acts are not always so insane if you have the whole picture. It all depends on context and the availability (or lack) of information. If you lack information or if you even are fed the wrong information anything could be made to seem inexplainable or outright evil.

It seems to me that 3) is a convenient blame to not having to bother to dig up that information if it exists.

Edit clarification: Saying that something seems insane (to me) is saying that "I can't make sense of this - given the information I have". But saying "I lack information - therefore it would not make sense to gather more information" - then the image of the crime as being an act of insanity becomes a self-fulfilling prophecy.

  • There's an interesting shift in your answer compared to the question as worded that makes your answer poor. But it also highlights an interesting part of the question -- you shift from heinous acts to insane acts. Insane acts would be by definition be acts without reason on some definition. Heinous acts need not be so. Beyond that, I do think it's fair that there are epistemic issues.
    – virmaior
    Dec 2, 2015 at 8:54
  • Well the main problem as the question is formulated is that insane in it's definition is that "I can't percieve how this would make sense". Another way of putting that sentence would be "I lack the information to make sense of this". Dec 2, 2015 at 8:57

Very often an insane person is insane just in one particular way. For example, if I heard voices telling me that you are an evil alien who wants to destroy the world, and I believed these voices, that would be insane. But I could apart from this minor point of insanity be a completely sane and rational person, whose actions can be perfectly analysed by rational thought. (The rational thing to do would be to try and find evidence to convince others, in case of failure to assassinate the evil alien, or to figure out that I can't do anything about it and live my life ignoring the evil alien among us, and a person with that single one spot of insanity might do one of these rational things).


It is common to say that a person who commits a terrible crime is insane, and that his insanity is due to illness, or a form of illness or something vaguely along those lines. This kind of statement is false. An illness is a chemical or structural abnormality in your body. Such an abnormality can't cause a person to do anything. To say that a person who commits a terrible crime did it as a result of a fault in his body is like saying there is a fault in your television because you find one of the programs on the television distasteful.

A person who commits a crime, any crime at all, does so for a reason. Their reason may be stupid, or wicked, or both, but it is a reason. A person who shoots a load of people can think, as illustrated by the fact that he has to think about where to aim the gun.

Saying that a person who commits such a crime is insane is just a heavily disguised moral judgement. We would be far better off if people stopped disguising their moral judgements in this way. Calling people insane makes it difficult to discuss the behaviour of the criminal properly, and makes it difficult to criticise standards.

For an extended discussion of this issue and many others see "Insanity: the idea and its consequences" by Thomas Szasz.


Is it a fallacy to say that a sane person cannot apply rational thought to the motivations of the insane?

Yes, it is false to say that a sane person cannot apply rational thought to the motivations of the insane. Unlike intent, tho, motivation is imponderable. Imponderables cannot be rationally assessed - a truth value cannot be rendered. Like the conclusions of psychology (e.g. an application of rational thought to the psychopathological), rational speculations regarding motivation are opinions, not the confirmation of hypotheses. This is not to say that rational thought (e.g. logical reasoning) cannot be applied. Some opinions are of course more informed than others... but there is also a funny line between rational thought and rationalization. Often the mind believes it is thinking when merely passing from one metaphor to the next, eh?

It does not follow that a heinous crime is only committed by the insane unless ones presumes only the insane can commit heinous crimes.

The conclusion is also false - cause and catalyst can be ascribed whether the ascription is accurate or not.


Yes, there are two fallacies in this argument. Premise 2 and 4. I will address them in order and attempt to address them to make a similar set of premises.

Firstly, Premise 2 contains a fallacy because one does not need to be insane to commit a heinous act. Here are a few clear examples where this premise is inaccurate; a sadistic who derives pleasure from the suffering of others, a desperate actor where the heinous act was the only option for survival, a devoted follower instructed by the authority commit the act. Since there are a wide range of motives that could drive someone to commit even the most heinous acts, the premise can't stand as is.

If instead, you look at your original Premises 1 and 2 as components of a single clause - defining Person A as insane - we can overcome this issue. Therefore, let's amend the original example to be the following:


1) Person A is insane

2) A sane understanding cannot be applied to the motivations of the insane.


3) A cause or catalyst cannot be ascribed to Person A's actions.

*NEW Premises 2 and 3 were modified so the actor, Person A, is the focus rather than an on-looker and the crime itself.

Examining the NEW Premise 3, there is a fallacy because the state of being insane may be considered cause and catalyst, which would refute the premise. However, I believe you are more focused on whether there is intentionality or responsibility of the actor. This is more difficult to distinguish because there are definitional complexities to it. It is dependent on whether you are talking about social judgment, legal distinction, or medical understanding.

Here are some additional questions that may help you unpack this idea.

  • Are you considering either legal or medical definitions of insanity?

  • Are you concerned with the ethical distinction of the insane compared to the sane, given an equally egregious offense?

  • What are the moral responsibilities and social expectations of an individual identified as insane?

  • Is someone who is not in control of their mental faculties responsible for their actions?

  • Is there a different consideration for someone, in an insane state, who acts in an ethical way in accordance with their insanity? If a person is suffering from a paranoid delusion and acts out in accordance with that delusion, are they ethically responsible?

i.e. Person A believes Person B is the devil, and killing the devil will save the world, is Person A acting ethically?

  • It is a bit hard to follow from your post what exactly your answer is. I would rephrase your post to start with (1) do you affirm it is a fallacy or deny, and then (2) include only what is necessary to show that it is or is not. Much of this post seems to be raising further questions (which, while potentially interesting in themselves, don't address whether the proposition at hand is a fallacy or not). Apr 18, 2016 at 4:00

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