 In doing so, it is helpful to distinguish between fallacies which do and do not have non-fallacious instances. Equivocation, post hoc ergo propter hoc, non sequitor and hasty generalization are commonly classified as forms of argument that are inherently mistaken. In contrast, traditional fallacies like ad hominem, two wrongs reasoning, guilt by association, and appeal to pity are patterns of reasoning which can, when they are constructed in the right way, play a legitimate role within real life reasoning (and are, in view of this, sometimes treated as argument schemes rather than fallacies). 