The evaluation of Athir al-Din al-Abhari’s view on fourth figure of syllogism

Aristotle commences controversial debate with introducing three figures of syllogism. Then, the fourth figure was added to syllogism. In contrast to the other three figures which have a few discuses, the fourth figure has a lot of discussion and disagreements about conclusion conditions. Three controversial difference can be seen in this figure: (1)The worth of it (2) The conclusion conditions (3) the valid types of fourth figure. Some logician Before Athir al-Din al-Abhari (from Ibn Salah Hamedani to Afzal al-Din Khaneji), which are called antecedents accepted five valid types of the fourth figure under specific conditions and some logicians after him accepted eight valid types. It is worth mentioning that Abhari in some circumstances added three valid types to the five accepted types of fourth figure. Some of logicians after him (Taftazani, Hajj Molla Hadi Sabzavari) accepted eight types without any attention to these circumstances. We investigate the background of the fourth figure and its conditions. After approving the primary idea, we concentrate on the rootes of this mistake and show that the misunderstanding about Abhari’s phrases was caused the expansion of his idea in modality syllogism to syllogism in general.