The conventional wisdom in science is that the modern atomic theory, first formulated by John Dalton in the 19th century, comes from the tradition of ancient philosophical atomists like Democritus and Epicurus. Countless textbooks repeat this as a truism and blame the influence of Aristotle's philosophy for suppressing atomism, and with it scientific knowledge and human progress.1
But the story is vastly oversimplified.
For one thing, modern atomic theory rejects many central ideas of ancient atomism. For another, Aristotle himself believed there were indivisible parts of matter, termed minima.2 Medieval commentators developed the idea within Aristotle's system and important features of their thought found their way into modern atomic theory.
As one history of the concept "atom" puts it,
Dalton conceived the union of the atoms in the compound as a simple juxtaposition. The atoms lie against each other without undergoing any internal change. In this point the founder of the chemical atomic theory did not differ from the philosophic atomists, but simply continued as something quite natural the tradition of the preceding centuries. There is, however, a remarkable point of difference from the ancient philosophical atomism. Dalton's atoms are specifically different for every kind of substance. Even this is nothing new, for the prevailing medieval theory of smallest particles, the minima theory, knew minima of a specific nature, and it was in the circles of its supporters that the first efforts were made towards the more scientifically oriented corpuscular theories of the seventeenth century. The idea of specifically different smallest particles was already so firmly established that the official supporters of Democritus and Epicurus in the seventeenth century had made room for it in their atomic theory.3
The history of the atom, like many of the stories we scientists tell ourselves, is not so much true as a useful abstraction. The problem comes when the usefulness serves not to open us to reality, but to provide an anodyne against "details" that don't quite fit the way we like to see things.
More historical myth busting here: Flat Earth Flat Wrong in which we see that the big lie is not so much the idea of a flat earth, but the idea that anyone believed in a flat earth.
1. E.g., Silberberg, Chemistry, 4e (McGraw-Hill), p. 39. Of course for secularists Aristotle is a convenient whipping-boy for Medieval Christianity.
2. E.g., Physics I, 4, 187b 28-34. See Van Melsen, p. 42.
3. Van Melsen, p. 139.
Andrew G. Van Melsen, From Atomos to Atom: The History of the Concept ATOM, trans. Henry J. Koren, (New York: Harper and Brothers, 1960).