Of God and His Creatures

Porphyry wrote in Greek, where phusei ('naturally') is often used in the sense of 'thoroughly' (cf. Eph. ii, 3). It is Shakespeare's 'in grain,' as 'a fault in grain' (Comedy of Errors, II, 3). In a thoroughly wicked man wicked habits have grown into a sort of second nature.

Of God and His Creatures: 3.107