Atomism

Atomism is the view that matter consists of discrete, indivisible or fundamental microscopic constituents. Different versions disagree about what those constituents are and how they behave.

Leucippus: A Greek philosopher traditionally credited with founding atomism alongside Democritus. Ancient sources associate him with the earliest Greek formulation of atoms and void.
Atom: A basic unit of a chemical element, with a nucleus surrounded by electrons. Modern atomism identifies ordinary matter's chemical building blocks as atoms.
Atomic theory: The scientific account that matter consists of atoms with characteristic structures and interactions. It turns the broad atomist claim into a testable theory of matter.
Continuum mechanics: A framework that models matter as continuously distributed rather than as discrete particles. It describes material behavior without representing individual atoms.
Democritus: A Greek philosopher who developed an influential account of reality as atoms moving through void. His surviving reputation made ancient atomism its best-known philosophical form.
Void: An absence of matter or physical contents, understood differently across philosophical and scientific theories. Ancient atomists required empty space for atoms to move.
Brownian motion: The irregular movement of microscopic particles suspended in a fluid, caused by collisions with its molecules. Its measurable statistics provided evidence for unseen molecular motion.
Hylomorphism: Aristotle's account of concrete substances as composites of matter and form. It explains material things through form and matter, not only constituent particles.
Epicurus: A Hellenistic Greek philosopher who adapted atomism into a naturalistic account of the world and human life. He made atoms and void central to a systematic philosophy.
Indivisibility: The property of having no parts into which something can be divided. Early atomists defined their fundamental constituents as indivisible.

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