This paper carries out full analysis on Aristotle s theory on categorical proposition and points out that he introduced,for the first time in logic history,term variable,established opposition matrix,and laid basis for syllogism.

Matching up to the three indispensable conditions to conversion inference of categorical proposition in traditional logic is in fact proved to be the restriction of interrelation between lexical items that the conversion inference concerns, as is visually cleared by Eulerian graph.

Is it universally adequate that the reasoning rule "if a term is not distributive in the premise, it is still not in the conclusion" in the reasoning consisting of categorical propositions? This is a question that has not been resolved in logic.