Aristotle.

Atomism (Greek atomos, meaning “uncuttable”) is a natural philosophy that developed in several ancient traditions. The atomists theorised that the natural world consists of two fundamental parts: The indivisible atoms and the empty void.

Aristotle said that atoms are indestructible and immutable and there are an infinite variety of shapes and sizes. They move through the void, bouncing off each other, sometimes becoming hooked with one or more others to form a cluster.

Clusters of different shapes, arrangements, and positions give rise to the various macroscopic substances in the world.

References to the concept of atoms date back to ancient India and ancient Greece. Carvaka school of atom-ism may date back to the 6th century BCE. The Nyaya and Vaisheshika schools later developed theories on how atoms combined into more complex objects.

In the West, the references to atoms emerged in the 5th century BCE. Whether Indian culture influenced Greek or vice versa or whether both evolved independently is a matter of dispute.

Of importance to the philosophical concept of atom-ism is the historical accident that the atoms which were thought to be indivisible, were found in the 20th century, to be composed of even smaller entities.

However, the possibility that these too might be composed of still smaller particles cannot be ruled out.

Although the connection to historical atom-ism is at best tenuous, these particles, rather than chemical “atoms”, are roughly analogous to the traditional indivisible objects.