The pre-Socratic Ionian Greek philosopher Heraclitus (c. 535 – c. 475 BCE) used the word logos ('word') to describe a kind of law which keeps the cosmos in harmony, moving all objects, including the stars, winds, and waves. Anaxagoras (c. 500 – c. 428 BC), another Ionian philosopher, introduced the concept of nous (cosmic mind) as a ordering force.