Abstract

Some scholars have claimed that Avicenna was the first logician to prove the Barcan formula, its converse, and the Buridan formula. However, I will show that this is not the case, and that Avicenna was not particularly concerned with implications between de re and de dicto modality. It is likely that Khūnajī was the first Arabic logician to explicitly endorse some implications between the de re and de dicto modality as well as the so-called Barcan formula, its converse, and the Buridan formula. In this paper, I have examined Khūnajī’s account of these implications.