The most important topic in logic is deduction which is treated in logical books under the heading of argument. Ancients divided argument into the three classes of syllogism, induction and analogy. As to kinds of and the sort of division of argument some questions has been raised. On the one hand, besides the theory of syllogism which is without doubt Aristotle's masterpiece one of important works of Aristotle's in the field of logic is the topic of "conversion", "contradiction" and "contrast". Of course, in Organon these topics have been treated incidentally. Ibn Sina added some relations to those which Aristotle had introduced and by finding the similarity of these topics brought them together in his logical works. After Ibn sina, logicians by following him introduced these relations under the heading "representative argument". The same topic has been treated in recent books of traditional logic with the title "rules of proposition". This title suggests that these logicians regard "rules of proposition" as a kind of deduction and argument. In this article the author defends the latter view and by assuming the conversion to be a kind of argument and examples like that has proposed a division of deduction in which the place of these arguments has been clearly defined and has no difficulties of previous division.
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