Bad Reasons Fallacy

Taxonomy: Logical Fallacy > Formal Fallacy > Bad Reasons Fallacy*

Subfallacy: Fallacy Fallacy

Form:

Argument A for the conclusion C is bad.
Therefore, C is false.

Exposition:

This fallacy consists in arguing that a conclusion is false because an argument given for it is bad. There are two main ways for an argument to be bad:

  1. At least one of the reasons given for the conclusion is bad―that is, false.
  2. The reasoning of the argument is bad, that is, the reasons given do not support the conclusion strongly enough to meet the burden of proof.

It's always possible to give a bad argument for a true statement, and that doesn't mean that a good argument for it cannot be found.

Exceptions:

In some cases, such as legal trials, where there is a presumption in favor of one side and a corresponding burden of proof on the other, it is legitimate to reason that a proposition is false if all of the reasons given for it are bad. For instance, in a criminal trial in which there is a presumption of innocence, the jury should conclude that the defendant is not guilty if all of the prosecution's arguments for guilt are uncogent. However, it would still be fallacious to conclude that the proposition is false just because one argument for it is bad, unless it is the only possible argument.

Similarly, when dealing with implausible claims that are presumptively false, it is not fallacious to reject such a claim when the evidence offered for it fails to meet the burden of proof. For instance, conspiracy theories and pseudoscientific claims are highly improbable and the burden of proof is on their proponents. Yet, the evidence offered by such proponents is often weak or non-existent, which is why it is not wrong to reject their theories.

Exposure:

One way that a deductive argument can be bad is for it to be unsound, that is, for it to be invalid or to have at least one false premiss. As a result, there are two versions of this fallacy when argument A is deductive:

  1. Argument A has a false premiss. If an argument has a false premiss, then even if it is valid, it fails to prove its conclusion. However, this does not show that the conclusion is false, as it's possible to give false premisses for a true conclusion.
  2. Argument A is invalid. If an argument is invalid, then even if its premisses are true, it fails to prove its conclusion. However, this does not show that the conclusion is false, for it's possible to argue invalidly for a true conclusion.

Since the conclusion of a sound argument must be true, it's tempting to think that the relation between the unsoundness of an argument and the falsity of its conclusion is parallel, that is, that the conclusion of an unsound argument must be false. However, the conclusion of an unsound argument may be either true or false. Misunderstanding this asymmetry between sound and unsound arguments is probably one psychological source of this fallacy.

*Note: Nigel Warburton, Thinking from A to Z (Second Edition, Routledge, 2001), pp. 25-26