How to Avoid Common Logical Errors

Avoid Non Sequiturs

• "Non sequitur" is Latin for "it does not follow." When an argument is a non sequitur, its conclusion does not follow from its premise(s). This term is often used to refer to particular types of arguments that clearly do not follow from their premises and never could.

  For example, any argument that takes the following form is a non sequitur:

  Step 1: If I am a goat, I am a hoofed creature. Step 2: I am a hoofed creature. Step 3: Therefore, I am a goat.

  It is clear that this argument does not follow. Even if the premises and conclusion were all true, the conclusion is not a necessary consequence of the premises. This sort of non sequitur is also called "affirming the consequent."

  Another common non sequitur is this:

  Step 1: If I am in Rome, I am in Italy. Step 2: I am not in Rome. Step 3: Therefore, I am not in Italy.

  The speaker could be in many other places in Italy. This sort of non sequitur is called "denying the antecedent."