/ˈlɒdʒɪk/
[noun] The study of clear and correct reasoning, or a particular way of thinking about something that makes sense and follows clear rules. It helps people decide if an argument is good or bad.
Logic's Greek root 'logos' meant not just reason but the entire fabric of the universe — the hidden order holding all things together.
The story of 'logic' begins in ancient Greece, with one of the most powerful and wide-ranging words in any language: logos. For Greek thinkers, logos was far more than a word for reason or argument. It referred to the underlying principle of order in the cosmos — the rational structure that made the universe intelligible. When the philosopher Heraclitus wrote that all things follow the logos, he was saying that reality itself is organised according to a kind of deep, rational pattern. The word came from the Greek verb legein, meaning 'to speak' or 'to gather', suggesting that reason and language were, for the Greeks, inseparable activities.
From logos, Greek built the adjective logikos, meaning 'of or relating to reason or speech'. This gave rise to the phrase logike tekhne, literally 'the art of reasoning', which is the direct ancestor of our word. It was the philosopher Aristotle who, in the 4th century BCE, turned logic into a formal discipline. His collection of works on the subject, later called the Organon or 'instrument', laid down the rules of deductive reasoning and the syllogism — the idea that if two premises are true, a conclusion must follow. Aristotle did not use the word 'logic' himself as a title, but his systematic approach gave the concept its permanent shape.
The Greek logike passed into Latin as logica, keeping its meaning intact. Latin was the language of scholars across medieval Europe, and through it the concept of formal reasoning was transmitted to the universities of the Middle Ages. Medieval scholars debated logic ferociously — it was considered one of the three foundational arts of educated thought, alongside grammar and rhetoric, forming the trivium that every student had to master. The word logica travelled across Western Europe bundled inside this educational tradition.
English received the word in the 14th century, most likely through Old French logique, which itself came directly from Latin logica. So the full chain runs: Ancient Greek logike → Latin logica → Old French logique → Middle English logik or logique → Modern English logic. At first, the English word referred almost entirely to the academic discipline — the formal study of valid argument taught in universities. It was the language of scholars and theologians, not of everyday conversation.
Over the following centuries, the word gradually broadened. By the 17th and 18th centuries, as science and philosophy flourished, 'logic' began to be used more loosely to describe any kind of clear, systematic thinking — not just the formal rules in a classroom. You could speak of the 'logic' of a business decision or the 'inner logic' of a story. This metaphorical widening reflects how deeply the concept had been absorbed into English-speaking culture. Today we use it both in its strict philosophical sense and in everyday speech to mean little more than 'common sense' or 'a reasonable explanation'.
Perhaps the most surprising thing about the word is how much its root, logos, spread into English through other routes simultaneously. The suffix -logy — as in biology, geology, and psychology — comes from the same Greek logos, meaning 'the study of'. So does the word 'dialogue' (Greek dialogos → Latin dialogus → Old French dialogue → English dialogue), meaning a reasoned exchange between two people. Even the word 'logarithm' carries logos inside it. Logic, in other words, is not just a word about reason — it is a root that has quietly organised a large part of the English language itself.