A fallacy is simply a faulty argument a pretender.
Formal fallacies deal with the actual form of the argument.
When an argument is structured incorrectly it is fallacious. But even when an argument is formally correct it may still be informally fallacious. The conclusion may not actually follow from the premises due to a faulty gathering of information, circular reasoning, etc. Informal fallacies are the more common of the two types of fallacies, and will be covered below. Informal Fallacies Informal fallacies are the most common examples of faulty reasoning.