Aristotle developed the syllogism, a key tool in deductive reasoning. A syllogism reaches a conclusion from two premises, such as “All humans are mortal; Socrates is human; therefore, Socrates is mortal.”
Aristotle gave this form of reasoning its first systematic treatment in Prior Analytics, part of his wider collection of logical works known as the Organon. He analyzed how terms function in premises, identified different syllogistic figures, and distinguished valid argument forms from invalid ones.
The syllogism does not guarantee that the premises are true; it shows whether the conclusion follows correctly if those premises are accepted. This distinction is why deductive logic differs from experimental science, which must also test its starting assumptions.
Socrates and Plato influenced Aristotle’s philosophical thinking, but neither created the formal theory of syllogistic reasoning. Later Greek, Islamic, and medieval European scholars expanded Aristotle’s work, which remained central to Western logic for centuries.