Logical fallacies are errors in reasoning that undercut an argument or thesis. On the surface, fallacies may seem to strengthen an argument, but in fact they rarely hold up to critique or rebuttal. Logical fallacies are often identifiable by a lack of evidence to support their claim.
There are several dozen logical fallacies, which can be roughly divided into formal and informal. Formal fallacies are those in which the error arises from the form in which the argument takes. For example, an appeal to probability is an argument in which something is assumed to be universally or always true because it is usually or probably true. Informal fallacies, on the other hand, require the examination of the argument's contents rather than its form. For example, an argument from silence describes a fallacy in which a conclusion is drawn based on the absence of evidence to disprove a certain point rather than evidence to prove a point.
The earliest remaining record of logical fallacies is Aristotle's "Sophistical Refutations." This text identifies 13 logical fallacies and categorizes them as Fallacies in the Language, or those created by deliberately misusing or obscuring words, and Fallacies Not in the Language, or those created by failures of reasoning or argument.