Letters 113.15

Again, no living thing is part of another living thing. But Justice is a part of the soul; therefore Justice is not a living thing. It looks as if I were wasting time over something that is an acknowledged fact; for one ought to decry such a topic rather than debate it. And no two living things are equal. Consider the bodies of all beings: every one has its particular colour, shape, and size.

Seneca, Letters to Lucilius 113.15, translated by Richard Mott Gummere