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 recognising 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 lacuna. ἡ γὰρ TERMὁρμή σου ἔστω — "for let your impulse be…" — and the text breaks off. 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. What exactly it was to be, Marcus did not finish writing or a copyist failed to transmit. Long honestly leaves the break standing: "let thy efforts be-". There is nothing to restore it from, and this corpus restores nothing.

How the entry looked in the source. In the text from which these passages entered the corpus, 12.17 and 12.18 stood run together, and at the seam the Greek numeral ιη′ — "18" — had survived. That is what marked the division: 12.18 begins with εἰς τὸ πᾶν ἀεὶ ὁρᾶν and is a separate entry in the manuscript tradition. The governing discipline is action, the sustaining one assent.