Not what’s true. What has to be true, given that something else is.
Logic doesn’t ask whether a claim is true — it asks whether a conclusion actually follows from its premises, a narrower and more mechanical question that can be checked without knowing anything about the subject matter at all. “All A are B, all B are C, therefore all A are C” holds regardless of what A, B, and C stand for.
Aristotle’s Organon, compiled in the 4th century BC, is the founding text: it introduced the categorical syllogism and dominated Western logical training for roughly two thousand years, absorbed into medieval scholastic education essentially unchanged. That long stability ended in the 19th century, when George Boole recast logic as algebra (logical operations as mathematical ones) and Gottlob Frege built a formal symbolic system powerful enough to express relations Aristotelian syllogism couldn’t touch — a shift so complete that modern formal logic is arguably closer to mathematics than to its own Aristotelian ancestor.
Source: King, C.G. & Raspa, V. (eds.) (2025). Aristotle’s Organon in Old and New Logic, 1800–1950. Bloomsbury Academic.