To be of sound mind is the greatest excellence and wisdom; to speak and act with truth, detecting things according to their nature” [or constitution]. (Sweet 112; my amendment; DK 112; Kahn 32)
Sweet translates sophronein as “sound mind.” Kahn translates it as “thinking well.” The term is a cognate of phronesis. It indicates being temperate and discrete, having self-control.
On sound mind as telos
There is a longstanding debate among scholars of Heraclitus about correct punctuation, as the punctuation strongly affects the meaning of the quotation: In particular it is not clear whether a comma should come after “greatest” (megiste). If it does not, as in Sweet’s translation, then Heraclitus is speaking of an excellence of humans, a telos. This would be the first such reference to human excellence (arete), understood philosophically, as a fundamental goal in Greek philosophy. Kahn, like Sweet, accepts the interpretation of this passage as entailing a telos. This also makes sense in light of Heraclitus’ view of action being guided in every case (F54) and of there being a “way” (F5) that many lose sight of. Such language hints of a goal or purpose to which we can be guided. Though F55 indicates “human nature has no set purpose,” it also indicates that “the divine nature has.” Sound thinking in accord with purpose then would be thinking in alignment with the divine, the true.
In some passages already explored, Heraclitus also notes that sound judgment is reserved for the gods (F55). In others, he relativizes this saying at least that to know oneself and think well belongs to all people (F29) and suggesting that human purposes can be informed by the divine. Here he appears to highlighting the latter view — the human potential for excellence and wisdom.
Truth in speech and action
It is important that Heraclitus is here connecting the achievement of “sound mind” with speech and action. Truth is not depicted here simply as a theoretical attitude. There is also a true way of acting. Heraclitus here is being a theoretical and practical philosopher. He is speaking of theory and practice. Indeed, the “thinking” pointed to is even manifest in action–“speaking” the truth.
True speaking and acting as Heraclitus here conceives of it involves an orientation toward things with respect to their “nature” or their “constitution.” Here the term used is phusin. It refers to an object’s natural qualities, constitution, or condition (Sweet, p. 49). Robinson avoids the term nature and speaks of “the real constitution of things” instead. This has the virtue of emphasizing the process character of Heraclitus’ thought. The focus of Heraclitus is not on a substance metaphysic, thus so much on “natures” or “essences.” Detecting things according to their constitution requires knowing the principle according to which they are guided (F54). It requires knowing the logos that guides all things in the process of becoming.