Once, there was a philosopher who unknowingly changed the course of science. His name was Leucippus, and he lived around the 5th century BCE. He was the first to propose something we now take for granted: that all matter is made up of invisible, indivisible particles. He called them atoms. Leucippus paved the way for Democritus, Epicurus, the natural philosophers of the Renaissance, and ultimately the foundations of modern atomic theory.

And yet, from this pivotal figure, nothing survives. No writings. No books. Not even a full fragment. Just a single sentence—preserved by chance in a later commentary on Aristotelian philosophy.

That sentence is:

«Οὐδὲν χρῆμα μάτην γίνεται, ἀλλὰ πάντα ἐκ λόγου τε καὶ ὑπ’ ἀνάγκης.»
“Nothing occurs at random. Everything happens for a reason and by necessity.”

Within this one brief line lies an entire worldview. A belief that the universe doesn’t operate by chance, but by cause and necessity. That behind what appears to be chaos, there is order—unseen, but very real.

Leucippus was likely born in the region of Miletus, as were many other early Greek natural philosophers. Some say he was from Abdera, others from Elea. Ancient historians disagree—and some even questioned whether he ever truly existed or if he was merely a construct of Democritus. But the impact of his thought is undeniable.

Everything we think today about the structure of the universe—electrons, molecules, particles, forces—can be traced back to that one revolutionary idea: nothing happens without a cause. And that idea began with Leucippus.

None of his writings have endured. But perhaps they didn’t need to.
Perhaps that one sentence was enough.