8 - Validity and Syllogism

Summary

The notion of validity and the systematic codification of valid forms of deductive argument are central to the discipline of logic. This chapter will reconstruct how, in antiquity, Aristotle and the Stoics constructed two different deductive systems meant to capture and codify an especially important subset of valid inferences, which they called ‘syllogisms’.¹ In the process, we will also emphasise some key similarities and differences between the two systems, and between both of them and modern conceptions of validity and formal logic. Because of space limitations we will not include in our presentation other interesting and for the most part subsequent developments in the classification of valid forms of inference.²