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I'm reading something on the topic of logic and one of the exercises asked me to convince myself that a contradictory statement was true. I could not convince myself of this and now I am curious about whether this illustrates some innate characteristic of noncontradiction in the human mind.

  • Isn't that just a disingenuous statement? Can you truly believe something like that? – James Jun 29 '14 at 0:36
  • That was quick. I deleted my comment and made it an answer. I don't regard that as disingenuous at all. When the OP asked about contradictions that are true, I thought of real life. It's clear you can't find examples in domains such as logic or math, by definition. As far as asking if I believe what I wronte ... Didn't you ever love and hate anything at the same time? – user4894 Jun 29 '14 at 0:41
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    I think a quick glance at politics on any day indicates that humans believe contradictions just fine... – commando Jun 29 '14 at 0:42
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    I don't think it is possible to believe that I love someone and hate them at the same time. Perhaps there are words other than 'love' and 'hate' that would better capture that kind of emotion without appearing to be contradictory. Taking that statement at face value must lead to a contradiction. – James Jun 29 '14 at 0:52
  • Recommended reading: Ruth Barcan Marcus is known for holding the view that contradictory beliefs are impossible. See her papers "Rationality and Believing the Impossible" and "Some Revisionary Proposals about Belief and Believing", both reprinted in her collection Modalities, NY 1993. For a recent reply to her arguments see Mark Richard: "Marcus on Belief and Belief in the Impossible". Theoria 78 (2013), 407-420. You can download this paper from Richard's homepage. – sequitur Jun 29 '14 at 13:39

10 Answers 10

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You need to distinguish at least three cases here.

Case #1: To believe consciously, at the same time , and with full understanding A and not A. In other words, this is the case where simultaneously believe that the world is flat and the world is spherical at the same time. This seems difficult if not impossible and might represent a feature of the human mind that we call "rationality." This is what Kant believed.

Case #2: To believe A and B which happen to be contradictory. This is called "cognitive dissonance" and can happen all the time. This is a classic problem in the philosophy of language. Specifically, it's actually a joke about Sartre where they ask if you can simultaneously hold to the claims:

(A) I love the author of a set of novels
(B) I hate the author of a set of philosophical works

Where it turns out that they are the same. The question that arises and this relates to Case #1 is whether you can hold these beliefs even in light of knowing that they are the same person. There are several different ways of accounting for this but I think the easiest one is to qualify what you hate and love and realize the content of the novels and philosophy differ in a meaningful regard.


A second version of case 2 is Hesperus and Phosphorus. These are two names for Venus which refer to the evening star and morning star respectively (the Greeks believed they were different). The problem in the philosophy of language is again whether reference matters. Is everything true of one true of the other? Frege writes on it extensively, Kripke has his own idea of a solution too. The basic problem has to do with what is going in naming.

Case #3: To believe approximation A which we know to be false. This actually seems perfectly rational and is common behavior in science. I for instance would use classical orbital theory when describing most types of chemical bonds (at least ones that involve the common non-metals), but I know it is not in fact true.


So really it's going to be hard to believe Case #1 type contradictions and that might say something about our minds. But we can also be quite resilient to drawing logical inferences when in Case #2 circumstances. Witness the large number of people who stay in abusive relationships.

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    For the second case there's also a nice classic morning star/evening star example. – user132181 Jun 29 '14 at 7:24
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    Yes the Hesperus and Phosphorous one. I know Kripke uses it. In philosophy of language, it goes back at least to Frege. – virmaior Jun 29 '14 at 8:06
  • I wonder whether cases 2 and 3 are related, with the approximation in case 2 being, "a person can be judged by their works" ;-) – Steve Jessop Jun 29 '14 at 11:38
  • @SteveJessop at best they are only tangentially connected. Case 3 often involves the conscious use of an abstraction that one knows is inadequate but efficient. Case 2 often involves being unaware (not necessarily unconscious) that one thinks is incoherent in a certain area. – virmaior Jun 29 '14 at 12:02
  • I think that in practice there's a degree of conscious approximation. When I say, "I hate Thomas Hardy" I'm very aware that I don't know Thomas Hardy, and that if by some accident of time travel I met him in a pub I couldn't confidently predict that I would find him unpleasant. His writing leaves me with an impression of the writer and I'm aware that such impressions are unreliable. But I certainly agree with you that case 2 need not always be this way. – Steve Jessop Jun 29 '14 at 12:18
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There's an ongoing discussing here between comments and answers about the definition of contradiction as asked by the OP. Since the question asked about the realm of logic, I'm going to provide an answer assuming that contradiction means the fact of statement A and not A to be held true at the same time.

OP asked why is it that humans cannot believe in contradictions, in the most literal sense of A and not A at the same time.

My take on it is that minds hold belief systems, complex networks of differently related facts with different certainty levels and relationships. This complexity of the networks is that gives rise to cognitive dissonance: facts that may have relationships to other facts which are contradictory indirectly.

The purpose of this network of beliefs is to be able to understand the world, predict it and interact with it.

Facts are as simple as logic proposes, little bits of knowledge of "X is true" and "Y is false". "X is true AND X is false" provides no information whatsoever, because nothing can be inferred from it, and endangers what related facts mean to it. A implies B, not A implies C, A and not A endangers the causality of A to B and not A to C.

This is why contradictions have this strange feeling into our mind: it endangers most of what we know. If statements are generic enough so that anything could be derived from them, contradictions on these statements are generic enough so that we may question everything we know. "This statement is false." is a great example.

(Notice I include paradoxes in contradictions, because the heart of a paradox is displaying one truth that contradicts itself.)

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"Why can't humans believe contradictions?" is a question of psychology rather than a question of logic. The core reason is cognitive dissonance.

Contrary to the answer by @virmaior, cognitive dissonance is not "To believe A and B which happen to be contradictory." Cognitive dissonance describes "the feeling of discomfort that results from holding two conflicting beliefs." (Although "conflicting" is a broader category than "contradictory", any beliefs that are contradictory are also in conflict with each other.) The essence of cognitive dissonance is not the conflicting beliefs but the psychological discomfort.

A lot of the time we find it difficult to put up with the discomfort and so prefer to change our beliefs. But most of us live through times when we might be aware of the discomfort but not aware of the contradictory beliefs that cause it. At times we are conscious of believing something but the way we act would indicate that we believe it's negation. At other times we might try to deny the discomfort (which creates another contradictory belief because we actually know at some level that we are uncomfortable) or mask it so that the two contradictory beliefs never confront each other in our consciousness.

But putting it simply, humans can believe contradictions but we tend not to because doing so makes us uncomfortable.

  • Very often people hold contradictory beliefs with no discomfort. Often they don't even realize they hold contradictory belief. For example consider the US Congress. Polls consistently show that Americans have an extremely low opinion of Congress. Yet at the voting booths, Americans overwhelmingly return their own Congressmen to office over and over and over for years. That is a classic example of human beings clearly exhibiting contradictory behavior with absolutely no discomfort at all. – user4894 Jun 29 '14 at 23:04
  • ps -- In other words people don't experience discomfort at their own contradictory beliefs. They rationalize them. That's why some contributors here are so offended at my suggestion that contradictions are the essence of real life. They literally do not see their own contradictory beliefs because they have already rationalized them away. With logic you can rationalize anything away. What you can't do is actually make that thing go away. You can only choose not to see it. – user4894 Jun 29 '14 at 23:11
  • user4894, I think you are using too broad a definition of "contradictory beliefs". Your real life examples ("I love you and I hate you", "low opinion of Congress" etc) are about beliefs that contrast with each other in ways that make it hard to predict people's behaviour. But those examples are not contradictions in the technical sense I think the OP is meaning. As @corsiKa pointed out in an earlier response to you, "I love you" and "I hate you" are not contradictory. And there is no contradiction between someone having a low opinion of Congress and voting them in again. – MattClarke Jun 29 '14 at 23:24
  • The OP said: "one of the exercises asked me to convince myself that a contradictory statement was true." Surely I have done my best to do that. I haven't even got an obligation to convince anyone else but at least I'm trying :-) Of course I agree that this exercise takes a bit of imagination. I am never going to convince myself that P & not-P is true. But life is complicated as @NieldeBeaudrap says; and it's in life that we very commonly accept and deal with contradictory beliefs. Any theory of AI, for example, must account for a collection of AI's exhibiting the Congress paradox. – user4894 Jun 30 '14 at 0:27
  • I think you're confusing the experience of cognitive dissonance and the existence of cognitive dissonance in suggesting I'm using the term wrong. Moreover, there's no reason I'm restricted to using the term as it is used in psychology... But the rest of your answer seems little applicable to what I took to be the meat of the question. The OP asked if difficulty (or impossibility) in believing contradictions is a feature of mind. And the answer is that it really depends on what you mean by believing contradictions. – virmaior Jun 30 '14 at 3:30
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Is it really so hard to believe two contradictory things at the same time? It may be irrational to do so - so let's examine some of the irrational moments of life. For example, have you ever experienced:

There is nothing behind me in the dark watching me and wishing me harm.
There IS something behind me in the dark watching me and wishing me harm.

Fears and phobias are irrational aspects of our personalities that can affect us even when we rationally know that there is nothing to be afraid of. Have you NEVER quickened your pace despite knowing full well that there's nothing that could possibly be there to cause you harm? Never laughed at yourself for being silly while still moving towards your destination just a tad quicker than one would call 'leisurely'

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I agree with the other users who believe that the context suggested by the term "contradictions" in this question is too broad. From a standpoint that is more narrow (and more formal), it would be impossible to believe that a proposition that one believes correctly describes a state of affairs in reality (i.e., a proposition that one believes to be true) is, at the exact same time, also not true according to precisely the same criterion for determining truth. It is only possible to believe one or the other of the two alternatives, but (in consideration of the Principle of Non-Contradiction) not both at the same time.

  • I generally agree assuming humans are subject to the law of non-contradiction. It's nearly impossible to actively maintain two claims that are contradictory. – virmaior Jun 30 '14 at 4:28
  • @virmaior Do you believe that it's impossible for any human being to actively experience a contradiction? Or do you mean that you personally cannot experience a contradiction? If the latter, I tell you that I experience contradictions constantly. But if you think your own personal sense of this is actually universal ... then I present myself as a counterexample. It is definitely possible for a person to experience logical contradictions in life. I am one such person. It's why I answered as I did. I'm actually surprised so few people share my view. – user4894 Jul 1 '14 at 18:22
  • I'm not sure what you even mean nor why you are talking about this in a comment thread about someone else's answer. In my comment above, I state "generally agree" and "nearly impossible" meaning I don't commit myself to the universal claim. But there's also several hedges in what you're saying and ambiguities. Referring to my own answer, I think if you simultaneously consciously can believe contradictory things without experiencing severe feelings of cognitive dissonance that you might want to get that checked. It's more likely you mean things you vaguely know are contradictory. – virmaior Jul 1 '14 at 22:18
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As I understand it, the OP question can be answered by the case represented by... I believe the earth is flat, and I believe the earth is not flat. These two statements form a contradiction (by definition). I am a human (by definition). Do I, or don't I, believe in this contradiction? The answers are: 1)I do believe that the two statements form a contradiction. 2)The contradiction, itself, can not be true or false. 3)Each contradictory statement can be true or false. 4) I can freely choose to believe which contradictory statement is true for me, but I can not believe that both (mutually exclusive) statements are true "at the same time" (by definition). This shows that the premise of the main question is false, humans can believe in contradictions.

In regard to convincing myself that a contradictory statement can be true, I can use the same example. For most people living in the 1200s, the statement "the earth is flat" was believed to be true. For most people living in 2014, the statement, "the earth is not flat," is believed to be true. Thus, I convinced myself that a contradictory statement can be true.

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Formally Virmaior is entirely correct. Formally, a contradiction is the joint believe that the statement A is B is both true and false at the same time and in the same respect. Formally A is B means that B is predicated of A, is said of A in some sense of being (with respect to the Aristotelian categories of being; see here for a simple analysis of his categories.

From the point of view of Aristotelian logic, the essential fact is that of the relationship between metaphysics, which addresses the question: 'What is true of reality?' and epistemology, which addresses the question 'How do I know what is true of reality?'. The latter depends on the former, and not the other way round. The nature of reality must (if we wish to avoid error) determine our way of thinking about reality. The law of non-contradiction has therefore two aspects: 1. That reality (or any part of it) is what it is, has an identity determined by its nature. 2. Then to properly grasp or identify the facts of existence, one must grasp the law of identity as primary: A is A. A thing is what it is. Therefore ones epistemology, to avoid conceptual contradictions, must be based on the law of identity.

But one's concept formation is open to volitional choice, so there is no physical law forcing our minds to be logical or non-contradictory. However, when we discover that we are holding a contradiction, we have a choice: 'What shall I do about this contradictory set of beliefs?' Again, we are free to choose if, when, and how to resolve such contradictions or not to seek such resolutions. Why choose to resolve contradictions? That depends on how much we value being true to the facts of reality as against how much we value our existing beliefs. Again we must choose. Most important is the fact that reality contains no contradictions, so if we want to achieve true knowledge and the values that depend on such knowledge, we must care about resolving known contradictions insofar as we know them to have direct bearing on our consciously held values. So, in the end, yes. We may choose to hold or ignore contradictory beliefs.

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Here's Aristotle's famous reductio ad absurdum of those who do not follow the principle of non-contradiction (Metaphysics IV 1007b19):

  1. Furthermore, if all contradictories are true of the same subject at the same time, it is evident that all things will be one. For the same thing will be a trireme, a wall and a man, if it is possible either to affirm or to deny anything of everything.
  2. And this is what must follow for those who agree with Protagoras’ view. For if it appears to anyone that a man is not a trireme, it is evident that he is not a trireme; so that he also is a trireme if contradictories are true. And thus there arises the view of Anaxagoras that all things exist together at the same time, so that nothing is truly one. Hence they seem to be speaking about the indeterminate; and while they think they are speaking about being, they are speaking about non-being; for the indeterminate is what exists potentially and is not complete.
  3. But the affirmation and the negation of every predicate of every subject must be admitted by them; for it would be absurd if each subject should have its own negation predicated of it while the negation of something else which cannot be predicated of it should not be predicated of it. I mean that, if it is true to say that a man is not a man, evidently it is also true to say that he is not a trireme. Therefore, if the affirmation is predicable of him, so also must the negation be. But if the affirmation is not predicable of him, the negation of the other term will be predicable of him to a greater degree than his own negation. If, then, the latter negation is predicable of him, the negation of trireme will also be predicable of him; and if this is predicable of him, the affirmation will be too. This is what follows, then, for those who hold this view.
  4. And it also follows for them that it is not necessary either to affirm or to deny. For if it is true that the same thing is both a man and a not-man, evidently it will be neither a man nor a not-man; for of the two affirmations there are two negations. And if the former is taken as a single proposition composed of the two, the latter also will be a single proposition opposed to the former.
  5. Again, either this is true of all things, and a thing is both white and not-white, and both being and not-being, and the same applies to other affirmations and negations; or it is not true of all but is true of some and not of others. And if not of all, the exceptions will be admitted. But if it is true of all, then either the negation will be true of everything of which the affirmation is, and the affirmation will be true of everything of which the negation is, or the negation will be true of everything of which the affirmation is, but the affirmation will not always be true of everything of which the negation is. And if the latter is true, there will be something that certainly is not, and this will be an unshakeable opinion. And if that it is not is something certain and knowable, more known indeed will be the opposite affirmation than the negation. But if in denying something it is equally possible to affirm what is denied, it is necessary to state what is true about these things, either separately (for example, to say that a thing is white and that it is not-white), or not. And if it is not true to affirm them separately, then an opponent will not be saying what he professes to say, and nothing will exist. But how could non-existent things speak or walk, as he does? Again, [according to this view] all things will be one, as has been said before (336:C 616), and man and God and a trireme and their contradictories will be the same. Similarly, if this is true of each thing, one thing will differ in no respect from another; for if it differs, this difference will be something true and proper to it. And similarly if it is possible for each to be true separately, the results described will follow. And to this we may add that all will speak the truth and all speak falsely; and that each man will admit of himself that he is in error. And at the same time it is evident that up to this point the discussion is about nothing at all, because our opponent says nothing. For he does not say that a thing is so or is not so, but that it is both so and not so; and again he denies both of these and says that it is neither so nor not so. For if this were not the case there would already be some definite statement. Further, if when the affirmation is true the negation is false, and if when the negation is true the affirmation is false, it will be impossible both to affirm and to deny the same thing truly at the same time. But perhaps someone will say that this was the contention from the very beginning.

See: John N. Deely's Four Ages of Understanding p. 125-126 (§ "How to Deal with Contradictions?").

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According to Eysenck, fascists, racists, all kinds of -ists, can easily believe contradictory things about their victims. They can easily think that one group of people is too lazy to work, and trying to take our jobs away (and that's he says is the difference to the merely prejudiced who can believe bad things about people without evidence, but not contradictory things. And who also can be convinced by evidence that their prejudices are wrong, at least in specific cases).

Convincing yourself of contradictory things is a lot easier when you want to believe both things. "Convincing" has to do with human psychology, not logic. For example, I'm one of the worlds best drivers, probably in the top 10%. On the other hand, the traffic in London is so awful, I would never get in and out of the town alive; I'm just not a good enough driver for that. Especially if you ask me to take you as a favour, and I don't really want to go. See, I can believe these two things simultaneously because one is good for my ego, and one stops me from paying for fuel.

  • I think there was a similar response by some to George Bush -- idiot and criminal mastermind or something like that. – virmaior Jul 1 '16 at 8:24
  • ime right wingers are more likely to respond to losing an argument without noticing, rather than blatant contradiction per se – user6917 Jul 2 '16 at 0:00
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I love you and I hate you. That's a contradiction that's often true. I want this piece of candy and I want to be skinny. That's another. Life is full of contradictions. The very definition of sanity is that you can get up every day and function despite all of life's contradictions.

If you were a complete sociopath you would be uninterested in and unmoved by the collective weight of human suffering.

If you were totally empathic with every living thing, and personally experienced the suffering of every creature in the universe, you'd die of grief the moment you woke up.

A sane person cares about human suffering; but not so much that it affects their own ability to care for themselves. A sane person must be part sociopath and part saint. That's another of life's contradictions.

It's only in abstract realms of thought that contradictions are false. In everyday life, they're often true. If you're told person X is shy, then if you know anything about human nature you know there's an exhibitionist hiding inside. And conversely if you see an exhibitionist, you know that inside they consider themselves shy.

Literally everything in life is the opposite of the way it appears. Everything is a contradiction.

This is why computers can not be conscious. Computers regard contradictions as false. How are you going to program a computer to understand that I'm tired and I don't want to go to bed? That I want to go to heaven and I don't want to die?

Logic is terribly limited in that it can only assign the value of FALSE to a contradiction. Life generally assigned contradictions a value of TRUE. Let's see anyone program that!

  • I don't see why this demonstrates anything about the ability of computers to be conscious. If computers "regard" contradictions as false (and I'm not even sure I believe that), it's only because we've programmed them to do so. There's nothing known keeping us from programming computers that think as we do, beyond the complexity of the task. – commando Jun 29 '14 at 0:41
  • @commando You're right, that claim is a bit of a stretch on my part. But programs are all about behavior; and consciousness is all about surfing the waves of contradictions of life. Maybe I don't have an argument here. If I assign values to eating candy and being skinny, perhaps all I'm talking about is decision theory, which can be programmed. But there really are a lot of contradictions in life and any theory of artificial consciousness does have to account for them. Or perhaps I'm wrong about all this. – user4894 Jun 29 '14 at 0:48
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    The part about computers at the end is plain wrong, along the lines of saying humans can't understand "maybe" because neurons are either firing or not firing. – Izkata Jun 29 '14 at 4:09
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    "I love you and I hate you" is different than "I love you and I don't love you". – corsiKa Jun 29 '14 at 5:28
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    A very empathetic -1. "I want this piece of candy and I want to be skinny" is no contradiction: the two wants are drives or priorities, not facts. They are priorities in conflict to be sure, but they do not entail a contradiction without a theory of how one should/does act on priorities. Life and goal-seeking is incredibly complicated, but one should never mistake complexity for contradiction unless one is prepared to abandon logic, and as an implicit consequence, the use of language as a way to describe distinctions. A post advocating contradictions can have no real place on a Q&A site. – Niel de Beaudrap Jun 29 '14 at 20:26

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