Diogenes Laertius, Stoicorum Veterum Fragmenta: SVF II.38b
Philosophy, they say, is like an animal: logic corresponding to the bones and sinews, ethics to the fleshy parts, physics to the soul. Another simile they use is that of an egg: the shell is logic, next comes the white, and the yolk in the center is physics. Or again, they liken philosophy to a fertile field: logic being the enclosing fence, ethics the crop, physics the soil or the trees…
Themes
Diogenes Laertius was a biographer of the Greek philosophers. Nothing is known about his life, but his surviving Lives and Opinions of Eminent Philosophers is a principal source for the history of Greek philosophy. He is assumed to have flourished in the first half of the 3rd century, during the reign of Alexander Severus (222–235 AD) and his successors