Changes

Converting a proposition without changing its quantity is called ''simple conversion''. When the quantity is reduced, as in the universal affirmative, it is called ''conversion per accidens''.

Converting a proposition without changing its quantity is called ''simple conversion''. When the quantity is reduced, as in the universal affirmative, it is called ''conversion per accidens''.

<ref>There is another kind of conversion omitted by Aristotle, but included within the scope of Aristotelian logic, called ''conversion by contraposition'', where the term contradictory to the predicate is given as the subject, and the quality of the proposition changed. thus 'All animals are sentient beings, therefore, a non-sentient being is not an animal.'  

<ref>There is another kind of conversion omitted by Aristotle, but included within the scope of Aristotelian logic, called ''conversion by contraposition'', where the term contradictory to the predicate is given as the subject, and the quality of the proposition changed. thus 'All animals are sentient beings, therefore, a non-sentient being is not an animal.'<ref>

===Structure of syllogisms===

===Structure of syllogisms===

The second book concerns the powers of syllogisms. Aristotle shews, in twenty-seven chapters, how many different powerful arguments can be constructed from syllogisms, and what figures and modes are best adapted to each. He also gives suggestions both to the person prosecuting the argument, and to the one who defends. This suggests that Aristotle introduced in his own school the practice of syllogistical disputation, instead of the rhetorical and dialectical techniques which the Sophists used in earlier periods.

The second book concerns the powers of syllogisms. Aristotle shews, in twenty-seven chapters, how many different powerful arguments can be constructed from syllogisms, and what figures and modes are best adapted to each. He also gives suggestions both to the person prosecuting the argument, and to the one who defends. This suggests that Aristotle introduced in his own school the practice of syllogistical disputation, instead of the rhetorical and dialectical techniques which the Sophists used in earlier periods.