An axiom of identity. A single line that dissolves a sham conflict: for the rational being (τῷ λογικῷ ζῴῳ), "according to TERMnature" and "according to TERMreason" are not two criteria but one. In the irrational, nature governs through instinct; to the human being nature gave reason — hence to act rationally just is to act naturally, and conversely. The classical source of the identity is DL VII 86: in rational beings reason "supervenes" as the craftsman over impulse, and life κατὰ λόγον becomes for them life DOGMAκατὰ φύσιν.

Why this line is in the notebook. The formula closes off the self-excuse every tired person reaches for: as though the "natural" (rest, anger, pleasure) were one thing and the "rational" (duty) another, with nature "demanding" a concession. Marcus cuts it off: the rational being has no two natures; to shirk the rational act is not "natural" but unnatural (cf. 06-33 — the toil proper to one's function is not παρὰ φύσιν; 05-01 — the morning "I rise to do a human's work"). At the same time the line is a bridge from the book's physics to its ethics: right after the hymn of the one TERMLogos (7.9) comes its practical corollary — the singleness of the measure of action. The discipline is action.