An informal fallacy occurs when the contents of an argument's stated premises fail to adequately support its proposed conclusion. In contrast to a formal fallacy of deduction, the error is not a flaw in the form of the argument. Though the form of the argument may be relevant, it is also the content that is implicated in the erroneous reasoning. So while formal fallacies always guarantee that the resulting argument is invalid, an argument containing an informal fallacy might employ a valid logical form while nevertheless remaining rationally unpersuasive.