A standard form categorical syllogism has two negative premises (a negative premise is any premise of the form 'No S are P' or 'Some S is not P').

Examples

1. "No Manitobans are Americans, and no Americans are Canadians, therefore, no Manitobans are Canadians." In fact, since Manitoba is a province of Canada, all Manitobans are Canadians.

Proof

Assume that the premises are true. Find an example which allows the premises to be true but which clearly contradicts the conclusion.