False Premise

All logical arguments are based up initial assumptions, called premises, that must be true for the conclusion to be true. Because the initial assumptions must not be false, it is important to scrutinize propositions before stating them. For instance:

a. All dogs have rabies. (Premise.)
b. Franco is a dog. (Premise.)
c. Franco must have rabies. (Conclusion.)

Because (a) is demonstrably false, (c) has to be false under this argument. That doesn't mean the dog mentioned does not have rabies, but it means you cannot prove it as above.

The real world is rife with this particular logical fallacy. Often this occurs when people make assumptions about the world around them. In the employment context, this might come up in wage claims, when employees extrapolate what happened to other to themselves; or in discrimination claims when employees make assumptions about another person because of their sex or race.

Watch out for these in all drafting employment manuals, too. Assumptions about how and when people act can accidentally impose contract law onto a poorly crafted handbook.