I noticed that in society, people use mental illness labels such as "psychopath", "autist", "narcissist" or "schizo" to dehumanize individuals and invalidate their thoughts, feelings and opinions on the basis that they are crazy and their philosophies are irrational (For example, a psychopath with narcissistic tendencies may try to preach his philosophy of egoism to others and people automatically label him first and assume he has nothing useful to offer)

But mental illness is a subjective concept, right? Mental illness is esentially just a sign of someone's brain-functioning and behaviour deviating from the general pattern of someone "normal". When someone goes to get diagnosed for a mental illness they are "not mentally ill" when they enter the room and "mentally ill" when they leave, so we don't actually know if anyone is mentally ill based on a subjective criteria (Greg might have just been a sad guy before he went to the doctor but now he has clinical depression). And mental illness is also hard to diagnose based off of deception as well. The psychopaths who are diagnosed are usually low-functioning ones but the high-functioning ones are skillful enough to hide it and therefore don't get diagnosed. And thus the image of a psychopath is associated with the low-functioning version, one who is emotionally unstable and impulsive because they are the ones who get caught, I'm sure if we knew what their motives were, many CEOs would be considered severely mentally ill as well. And each individual might see individual behaviours as crazy even though they are not officially mentally ill.

So would these peoples' philosophies still be accepted as valid philosophies by the philosophy community or would they be rejected on the basis that they can't think properly? After all, certain philosophies align with some of these mental illnesses, egoism, for example, aligns with a psychopath's instinct to preserve himself over others. Or a narcissist may hold the philosophy that the self has infinite potential. Or someone with autism may believe that humans have the same intrinsic value as all other objects (materialism?) due to lack of cognitive/affective empathy. Or someone with clinical depression may follow a pessimistic version of nihilism. Where do we draw the line?

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    It's the "illness" part that is subjective so as to whether a deviation from the norm is an illness or just different. So that illness is often not defined as deviation but as something that is harmful to the individual itself. That being said the features associated with that deviation don't need to be subjective.
    – haxor789
    Jan 8, 2023 at 2:34
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    why is everyone using 'subjective' to mean 'skepticism' @haxor789? actually, psychopaths tend to be quite good at moral reasoning. words like "psychopath" do to an extent just mean "i think you are evil", as it is also an informal term. the misuses of clinical terminology like 'borderline' on-line etc. i just find sad. but then i'm really such a depressive (haha)
    – user64154
    Jan 8, 2023 at 3:07
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    Philosophers do not reject or accept philosophies based on name calling or mental deviance, egoism is a perfectly fine philosophy, which is developed, discussed (including by non-egoists and without name calling) and has vast literature written on it. On those rare occasions when "mental illness" is used as more than ad hominem to discount claims, what is meant is not "deviance" but impaired judgment, i.e. that the person is less capable of arguing soundly, and so, given limited resources, it is impractical to have the claims discussed on merits.
    – Conifold
    Jan 8, 2023 at 8:21
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    Does a carpenter's physical illness imply that his furniture is non-functional? It is imaginable that a carpenter might have a physical illness which caused him to make shoddy furniture (and more imaginable that a mental illness might lead a philosopher to an unsound conclusion), but "imaginable" is a long way from "implies".
    – kaya3
    Jan 8, 2023 at 10:26
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    Why discuss person's philosophy with a counselor in a diagnosis room? There are academic journals for that, that is more practical. And persistent antisocial behavior that characterizes psychopathy is often not in one's self-interest (because it prompts massive adverse reactions and leads to inferior outcomes in common "prisoner's dilemma" situations), so consistent egoists themselves have a lot to criticize psychopaths for. Seriously, you'd be surprised how popular thoughtful egoism is among philosophers, read e.g. Mackie's Ethics.
    – Conifold
    Jan 8, 2023 at 11:32

5 Answers 5


To draw a conclusion as to the validity/soundness of a proposition/argument based upon the mental state of the person making it would be to commit a non sequitur.

Why? Because even a severely mentally ill person might, despite their illness, be more than capable of constructing perfectly cogent claims. A person's mental state is not a reliable predictor of the quality of the claims a person makes. A condition with paranoid and/or delusional traits might lead a person to more frequently make claims that fail to bear up to scrutiny, but the condition alone is a woefully insufficient indicator as to the truth value of individual claims made by a person suffering from such an illness. It would constitute a similar error to conclude that a person of entirely 'healthy mind' (if such a thing exists), will adhere to some imaginary flawless philosophy or will provide only unassailable arguments and irrefutable claims.

A claim is typically best evaluated against evidence and logic. This protects against a whole raft of logical fallacies, such as ad hominem, appeal to authority and appeal to faith (to name but a few).

  • This is technically correct and its basic point could be elaborated easily with many more subtle answers. Such is subtlety I guess haha
    – user64154
    Jan 8, 2023 at 0:07
  • @Crisis. I expanded para 2 slightly, but I'm more interested here in merely identifying the fundamental fallacy. Others may wish to further investigate the intricacies of mental health as it bears upon perception of and assessment of truth claims. Jan 8, 2023 at 0:31
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    This only applies to a third person. But what if you have a mental illness? Should you not take that into account and as such evaluate your judgments more closely? I would argue you should. It seems unreasonable to think a paranoid person wouldn’t let his fear affect his reasoning from time to time
    – user62907
    Jan 8, 2023 at 0:34
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    @temptrt. The question is, "Does mental illness imply that a person's philosophy is invalid?". The answer is clearly no, and I hope I've provided a relatively succinct explanation of why. The question of whether or not a person who suffers from a mental illness is capable of assessing their own claims is a different one. Jan 8, 2023 at 0:36
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    One notes that even invalid reasoning does not preclude a valid conclusion.
    – Mary
    Jan 8, 2023 at 1:11

So far the discussion has taken quite a "Mentalistic" approach - that since the conditions are enumerated in phenomenological terms that might be prone to societal or contingent trends, the proposed link from mental illness to illegitimate philosophical theorising can't be maintained.

However, a more "physicalistic" approach to this question would seem to hold some thought around evading this line of argument. Let's take, for example, Alzheimer's disease. Alzheimer's has a very clear physical interpretation - the sufferer's brain cells are dying, the brain is atrophying, and this is giving rise to the cognitive degeneration that is most clearly evident in their behaviours.

It seems uncontroversial to me to say that someone whose physical brain has degenerated to the point of being incapable of logically coherent thinking can no longer be held to be intentionally producing philosophical insights, however tragically far they may have fallen from their previous capability in the field. The parallel here is with other physiological disability conditions like blindness, deafness, paralysis - you are simply no longer capable of perceiving or acting in ways you were before, and so you are e.g. correctly not trusted to drive as a blind person until corrective surgery or some other form of rehabilitation takes place.

So, the question now becomes, what physical conditions do we include in this list? It seems incorrect to merely say that someone exhibiting sociopathic tendencies is automatically disqualified from weighing in on moral agency - however, if someone literally does not have a part of their brain that performs certain ethical calculations, shouldn't we at least recognize that their positions are going to be limited in their scope and application by this incapability?

Moving the discussion to the realm of the physical seems to evade the "subjectivity" opposition that would dominate in a purely mental conception of the personal subject.

  • "If someone literally does not have a part of their brain that performs certain ethical calculations, shouldn't we at least recognize that their positions are going to be limited in their scope and application by this incapability?". It may not be wise to rely upon them for ethical insight, but it remains a fallacy to discount any claim they make on the basis of their incapacity alone. The claim should generally be weighed upon its logical merits and evidentiary support. Jan 8, 2023 at 12:15
  • @Futilitarian, one could also make the same argument of randomly computer generated sentences, but the problem is how this contributes to the development of substantial philosophical positions, not just the truth value of an individual sentence. I'm not going to off-hand dismiss the potential truth in something my grandfather suffering from advanced dementia might say, but to defer to him as a source of philosophical authority in any coherently constructed area would be a very unwise decision.
    – Paul Ross
    Jan 8, 2023 at 12:38
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    To defer to anyone as a source of philosophical authority on the basis of anything but the demonstrable quality of their work (again, evaluated against logic and evidence) would be a mistake. No matter how bad his dementia is, if his arguments stand up on their merits, so be it (although this might of course be unlikely). When I read a philosopher's claims (no matter how great their reputation), I am assessing the claims alone, not any presumed or actual state of mind, or any professional status. Jan 8, 2023 at 12:51
  • The problem is exactly evidence, right? If someone is physiologically separated in some way from the body of facts that are at stake in the discourse, then even if they happen to say interesting sounding things, is what they're talking about the same thing? I'm not aiming to draw this line here in respect to metaethics or any other philosophical field, but to say that all that matters is the quality of the position invites the potential for some conditions to physiologically impede the formation of good positions, and if this question is to be resolved, that's where to look.
    – Paul Ross
    Jan 8, 2023 at 13:04

"Your argument is invalid because you are X" does not follow, but "Your argument is untrustworthy because you are X" can be a perfectly reasonable inference.

Suppose I observe that the prior probability of people with characteristic X making false conclusions under certain specific circumstances, P(False) is not small.

I observe characteristic X and those specific circumstances.

I observe that I have a nonnegligible false positive rate, P(Agree|False) in identifying true conclusions on cursory examination of such arguments.

I observe that I agree with such arguments in general at a certain prior rate P(Agree) = P(Agree|True)+P(Agree|False).

Calculate the probability that if I consider your argument and agree with it, it is false, using Bayes' theorem:

P(False|Agree) = [P(Agree|False) * P(False)] / [P(Agree|True) + P(Agree|False)]

If the left hand side is not small, it is reasonable for me to ignore your argument, even if I can't identify a flaw in it, if all that I know about you is that you have characteristic X and the circumstances are as specified.


Psychopathy is no mental illness. Its just different wiring of brain. Same for autism. Narcissism can be called mental illness if present in large enough quantity.

Neither of these de-humanize anybody. We don't call a machine narcissist or an animal autistic.

Mental illness is not subjective. There are very objective ways to tell whether a person is clinically insane. The most objective way to tell is whether a person's reasoning is correct i.e. if premises leads to conclusion. We all make logical mistakes but a person for whom not making a logical mistake is a rarity is ofcourse not right in head. Another test is, if the premises themselves are wrong.

For example a person see things others dont and such things have no reason to be there then such a person will be certified insane by a qualified doctor.

"Mental illness is esentially just a sign of someone's brain-functioning and behaviour deviating from the general pattern of someone "normal""

No, thats not how mental illness is defined. Its not fashion. You dont have to go with the crowd. You can be as different as you want. We don't label Einsteins and Newtons of the world insane. Its because they show us what they see and after they have shown us we can usually see too; and their reasoning makes sense because their premises (which we already usually verify) do leads to their conclusions usually (we check the facts about conclusion independently that the results do exist).

If you insist that there is a banana hanging in air and I cannot see it, nor touch it etc, and you are serious, then I will doubt a bit about your sanity. Its because what you tell don't match with data I have.

If you insist that you are getting weak because your late aunt's spirit steal all the food from your stomach then since we see you still making defecating materials we will doubt your sanity. In this case even though your premise is correct (you are getting weak, we can see that) your reasoning is wrong (if food is stolen from your stomach your body wouldn't be making the defecating materials because it need to have something to make something else, you don't make defecating materials on empty stomach, we have seen that many times).

As long as we keep data above we can verify both your premises and your reasoning.

There is another problem in your question. You are not distinguishing moral shortcoming with mental illness. See, you don't have to be insane to kill innocent people. You can be very clever as well as morally corrupt.



Irrationalism is a philosophical movement that emerged in the early 19th century, emphasizing the non-rational dimension of human life. As they reject logic, irrationalists argue that instinct and feelings are superior to the reason in the research of knowledge. The term has often been used as a pejorative designation of criticisms against rationalism as a whole.

The heart has reasons that reason cannot know. ~ Blaise Pascal

Paraconsistent Logic


Contradiction tolerant logics, the two above. The hallmark of "insanity", its pathognomic symptom, was/is contradiction.

A delusion (classic symptom of "madness") was once defined as clinging to a belief despite being offered strong evidence to the contrary (excludes religious & cultural beliefs). The bedrock of philosophy is evidence (re rationality/rationalism).

There's a fine line between genius and insanity. I have erased this line. ~ Oscar Levant

The eccentric genius is an easily recognizable character in many plays, novels, and films. Is it just a stereotype or is there a grain of truth in it?

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