Thomas Aquinas
That which is stated to be moved by itself is moved primarily. Therefore if one of its parts is at rest, it follows that the whole is at rest … Hence that which was stated to be moved by itself, is not moved by itself. Therefore whatever is in motion must needs be moved by another.
Source details
1259 · Summa Contra Gentiles I, ch. 13 — that nothing moves itself (a defense of the load-bearing premise)
Checked word-for-word against The Summa Contra Gentiles of Saint Thomas Aquinas · 2026-07-18