The Development of Modal Theory in Medieval Islamic Philosophy

From Ibn Sina to Nasir al-Din al-Tusi

Abstract

This Paper is intended as an investigation of the ‘Modalities (jihat)’ which were dealt with by Ibn Sina (d. 1037) and three post-Ibn Sin-an logicians, Abu al-Barakat al-Baghdadi (d. Ca. 1164), al-Suhrawardi (d. 1191) and Nasir al-Din al-Tusi (d. 1274).
The theory of ‘temporal modalities’, which Ibn Sina systematically constructed, is one of the important contributions in Islamic logic. In his Al-Isharat wa-al-Tanbihat he explained this theory at the end of the chapter on propositions and according to the components of proposition classified the ‘temporal modalities, ’ while he never classified modalities according to situation (amr).
Almost all the post-Ibn Sinan logicians received the concept of Ibn Sina's ‘temporal modalities.’ But al-Baghdadi introduced newly the distinction between ‘modality de re’and ‘modality de dicto’, which was used in medieval Latin philosophy, and by the concept of ‘cause (sabab)’ connected these two concepts from an natural philosophical point of view. al-Suhrawardi also distinguished these two concepts. But he went further and insisted on the thesis that all modalities de dicto are necessity (darura). This thesis can be explained by his plan of a ‘intuitionist logic.’
These two logicians, contrary to Ibn Sina, laid stress on situation (amr) and the epistemological value of modalities. Nasir al-Din al-Tusi, on the other hand, attached importance to the structure of proposition like Ibn Sina and proposed the theory of ‘triple modalities.’ He did not disregard the distinction between ‘modality de re’ and ‘modality de dicto’, but he did not use this distinction for the analysis of modalities. In fact, he stated that this distinction is important for excluding error about modalities.
In conclusion, among Ibn Sina and posf-Ibn Sinan logicians modal theories are not the same. Especially they are different in the epistemological value of modalities. Generally speaking, al-Baghdadi and al-Suhrawardi, on the one hand, constructed modal theory mainly from the epistemological point of view, and Ibn Sina and al-Tusi, on the other hand, constructed it from the structure of proposition.