Logical fallacies

A fallacy is simply a mistake in reasoning. Some fallacies are formal and some are informal. Sometimes, we can define validity formally and thus determine whether an argument was valid or invalid without even having to know or understand what the argument was about. In other words, we could define certain valid rules of inference. These inference patterns are valid in virtue of their form, not their content. That is, any argument that has the same form as a valid argument will automatically be valid. A formal fallacy is simply an argument whose form is invalid. Thus, any argument that has that form will automatically be invalid, regardless of the meaning of the sentences. In contrast, informal fallacies are those which cannot be identified without understanding the concepts involved in the argument.