Argument from consequences

The Argument from Consequences, also known as (‘Appeal to Consequences’) or argumentum ad consequentiam [1], is a fallacious argument that concludes that a belief is either true or false based on whether the belief leads to desirable or undesirable consequences.  Such arguments are closely related to the fallacies of appeal to emotion and wishful thinking.  They generally have one of two forms:

Positive form

Premise 1: If P, then Q will occur.

Premise 2: Q is desirable.

Conclusion: Therefore, P is true.

 Examples

  • Humans must be able to travel faster than light, because that will be necessary for interstellar space travel.
  • I believe in an afterlife, because I want to exist forever.

Negative form

Premise 1: If P, then Q will occur.

Premise 2: Q is undesirable.

Conclusion: Therefore, P is false.

Examples

  • Free will must exist: if it didn’t, we would all be machines.” (This is also a false dilemma.)
  • Evolution must be false: if it were true then human beings would be no better than animals.
  • God must exist; if He did not, then people would have no reason to be good and life would have no meaning.

Such arguments are invalid because the conclusion does not logically follow from the premises.  The desirability of a consequence does not make a conclusion true; nor does the undesirability of a consequence make a conclusion false.  Moreover, in categorizing consequences as either desirable or undesirable, such arguments inherently contain subjective points of view.

There are two types of cogent argument with which this fallacy is easily confused:

  1. When an argument is about a proposition, it is reasonable to assess the truth-value (whether it is true or false) of any logical consequences of the proposition.  Logical consequences should not be confused with causal consequences; and truth or falsity should not be confused with goodness or badness.
  2. When an argument concerns a policy or plan of action—instead of a proposition—then it is reasonable to consider the consequences of acting on it, because policies and plans are good or bad rather than true or false.

Endnote

[1] Latin for ‘argument to the consequences’

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