Theophrastus (372/1–282/1 Bce)

Language and Logic

Theophrastus made contributions to the theory of the syllogism (e.g., on the relation between the second and third figures), and he revised Aristotle's modal logic, suggesting that the conclusion has the same modality as the weaker premise, not the major premise (a weakest-link principle). He also proposed revising the system of dialectical predication, subsuming the four predicables under definition, perhaps to create "a single universal method" (frag. 124A–B), and he provided us with a definition of the dialectical topos" (not found in Aristotle) as an argumentative strategy or principle (frag. 122B). He is said to have introduced a doctrine of hypothetical syllogisms, possibly in collaboration with Eudemus of Rhodes (350–290 BCE). True to his reputation as a good speaker, his comments on language advance grammar and style, and he makes a notable effort to use appropriate language in each field.

Physics and Science

Of Theophrastus's work in the sciences, we still have two major works on plant taxonomy (Enquiry into Plants) and explanations for plants (De causis plantarum [Causes of plants]), famously influential on Carl Linnaeus (1707–1778); nine short tracts on the inanimate (e.g., winds, stones) and physiology (e.g., sweat, dizziness, fatigue); and fragments pertaining to meteorology, biology, epistemology, and psychology.

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