Two prohibitions and a sentence that breaks off. The entry consists of two short conditional periods built exactly alike: εἰ μὴ … μὴ πράξῃς / εἰ μὴ … μὴ εἴπῃς. Deed and word are set side by side and referred to different measures: an act is tested against the TERMκαθῆκον ("what is fitting"), a word against ἀληθές ("what is true"). These are two disciplines, action and assent, brought down to two lines; cf. 12.3, where the same pair appears as participles, and 12.15, where it appears under the names of virtues.

Why prohibitions rather than precepts. Both formulas are negative, and not by accident: a positive rule requires knowing what to do, a negative one only requires recognizing what may not be done. Such a rule is easier to hold in the head and harder to distort; cf. 4.2 — "let no act be done at random."

The break. ἡ γὰρ TERMὁρμή σου ἔστω, "for let your impulse be…", and there the chapter ends. Ὁρμή is a technical term: the impulse, the movement of the soul that issues in action and is the subject of the discipline of action. In Leopold the sentence runs on without a break into 12.18: the impulse is to be directed to seeing the whole and to analyzing the impression into its parts. Long took the place for corrupt and left the break standing: "let thy efforts be-". The governing discipline is action, the sustaining one assent.