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Appeal to consequences

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Cogito ergo sum
Logic and rhetoric
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General logic
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Dr. Sayer : We know that for a fact?

Dr. Ingham : Yes.
Dr. Sayer : Because?

Dr. Ingham : Because the alternative is unthinkable.
—Steven Zaillian - "Awakenings"

An appeal to consequences (also argumentum ad consequentiam), is a logical fallacy that the perceived outcomes of a proposition can determine its veracity. However, the utility of a belief is independent of its truth-value.

The fallacy is an emotional appeal and an informal fallacy.

Sometimes an appeal to consequences is called a pragmatic fallacy; this is incorrect. A pragmatic fallacy uses an example where something "worked" to argue for its general efficacy, while an appeal to consequences uses the effects of holding a belief to argue for the truth value of a proposition.

Alternate names[edit]

  • appeal to utility
  • appeal to convenience
  • argumentum ad convenientiam
  • appeal to consequences of belief
  • argument from adverse/beneficial consequences


The argument takes this form:

P1: If A is true then it implies, causes, or creates, B.
P2: B is, either subjectively or objectively, bad, immoral, or undesirable.
C: Therefore, A is false.

Or, conversely:

P1: If A is true then it implies, causes, or creates, B.
P2: B is, either subjectively or objectively, good, moral, or desirable.
C: Therefore, A is true.


Truth matters in logical debates; our emotions or feelings about the truth do not. While human emotions, feelings, and values will always influence what we decide to do based on our knowledge of the situation, that knowledge cannot be unduly influenced by our emotions or values if it is to be true knowledge.

This is applied fallaciously in arguing whether something is true or not. Just because something is perceived as having adverse consequences if it is true, does not make it suddenly become untrue — such an idea is just a form of wishful thinking. Conversely, when something is perceived as having good consequences if it is true, this perception does not actually make it true. Any argument from consequences is an appeal to emotion.


Sun Myung Moon:[2]

Some zoologists are saying the monkey is ancestor of the human. Then ask the scholar, "Sir, who is your grandfather? Is he a monkey? Then you are a descendant of a monkey." Will he like that? No way. It will turn him off. Would you like a monkey to be your grandfather?

Legitimate use[edit]

Public policy[edit]

It is generally not fallacious if used in decision making with something that isn't objectively provable, i.e., is this desirable, not is it true. This is found in political decision making, where the consequences, positive or negative, must be taken into account. There is no "real" political position, such as a tax rate or drug policy.

In these cases, the power of arguing from adverse consequences is directly proportional to the strength of the premise: for example, a proposal to discontinue a particular medicine because there are mild adverse effects (e.g. hair loss) in a small proportion of the cases would generally be considered dubious, while discontinuing the medicine because of serious adverse effects (e.g. early death or deformed babies) would generally be considered reasonable.

Since most acts will have both good and bad consequences, many of them unforeseen and unintended, it requires great care to deploy the argument from adverse consequences properly. Even using adverse consequences in decision making can be fallacious in some cases. The most frequent logical fallacy in this regard is when relatively small adverse effects are used to argue against practices with highly significant positive outcomes, e.g. that racial integration is bad because we no longer maintain separate bathrooms and water fountains which results in job losses for plumbers.

Epistemological nihilism[edit]

See the main article on this topic: Nihilism

In "If belief X then consequence Y", while consequence Y doesn't prove X true, consequence Y does prove Y "true" and 'If X then Y' "true". Epistemological nihilism is the idea that you can't know that you ever know or learn anything, e.g., you don't know that the world was created 5 seconds ago and all your memories were created along with it. This idea would indicate that 'if X then Y' can never be proven true, which can be countered with the argumentum ad baculum.

  • Bob argues for epistemological nihilism.
  • Alice throws something at Bob.
  • If Bob ducks, he must have known that not ducking would lead to pain.
  • If Bob does not duck, by his own logic Alice had no way of knowing that throwing things could injure other people.
  • Repeat until Bob stops arguing for epistemological nihilism.

While this doesn't directly disprove epistemological nihilism, it proves no one actually believes it to be true with total certainty. It is possible that someone believes it is true but also believes they could be wrong, and always acts on the assumption that they are. It's even more possible that it is one big exercise in reductio ad absurdum, since logically inferring based on past experience doesn't violate the premise whatsoever — people don't need to be certain before they act, in the way Bob doesn't necessarily know the object will hit him or be large enough to cause pain but might duck on reflex anyway.

Modus tollens[edit]

This is of course not to be confused with argumentation by contrapositive, or modus tollens. It is not a matter that the consequence is subjectively/objectively bad/immoral/undesirable if it does not occur in real life. The argument would go like this:

P1: If P is true then Q would happen/be observable.
P2: Q is subjectively/objectively bad/immoral/undesirable. does not happen/cannot be plausibly observed
C: Therefore, P is false.

An example would be the claims of psychokinesis. Assuming that people can in fact move things with their minds, even in simple acts such as Uri Geller's spoon-bending, there is no way to expect that everyone with such a power would be good or sane. People would be telekinetically snapping each others' necks left and right and we would definitely hear about that sort of thing on the news. Obviously, it can be deduced that, since society isn't a hotbed of psychokinetic violence like in the movies, these powers simply do not exist.

See also[edit]

External links[edit]