kathēkon, often rendered as ‘duty’ (‘Pflicht’), is a key term in Stoic ethics. The idea that it pertains to plants and animals as well as humans is generally accepted. For instance, Long and Sedley (1987, 365) write: ‘The breadth of reference of this term [sc. kathēkon] is indicated by the fact that it includes, at one extreme, activities of animals . . . or even plants as well . . .’
That Stoic physics controls ethics had been the general view prior to Annas (1993: 159-79), who denied any such blanket prioritization. This is the catalyst for Lorenz’s study, a dissertation submitted for a joint degree at the Universities of Cologne and Fribourg, which aims to show that physics does, in fact, drive the concept of the kathēkon (pp. 19-20).
The direction of such an investigation will be steered, to a large extent, by the weight assigned to the available sources, of which the principal ones are Diogenes Laertius, Arius Didymus/Stobaeus, and Cicero, De finibus 3. Lorenz gives preference to DL, who, though lacking in philosophical insight, is generally regarded as reliable in his Stoic book. Stobaeus (= SVF 3.494) is in general less reliable for the early Stoa in that he mixes Stoic doctrines of various periods, though on this topic he is acknowledged to provide useful material for explaining DL (p. 28). As to Cicero, Lorenz points to recent studies (Brunner 2010, Schmitz 2014) that have highlighted Cicero’s limitations as a reliable reporter of Stoic doctrines in Fin. 3. These pertain to certain details of his presentation of the doctrine of oikeiōsis, particularly the introduction of the Peripatetic idea of self-love, but do not necessarily invalidate his account as a whole. Possibly, literary considerations led Cicero to omit plants and animals from the Stoic presentation of oikeiōsis in Fin. 3 because he was reserving them for the Peripatetic version at Fin. 5.39-43. In any case, closer attention to Ciceronian texts might have benefited Lorenz’s argument (see below).
After the Introduction setting out the thesis and sources, the bulk of Lorenz’s book (Chapters II-V) is devoted to explicating DL 7.107, the first sentence of which reads: ‘They [the Stoics] assert that kathēkon is [something] which, once done (prachthen), has a reasonable justification (eulogon apologismon), viz., what is consistent in life (to akolouthon en zōēi), which also extends to plants and animals’. Lorenz highlights the difficulties translators have faced in finding an equivalent for kathēkon that both involves a ‘reasonable justification’ and applies to plants and animals. In this respect a traditional translation such as ‘duty’ (‘Pflicht’) will be too narrow; Long and Sedley, for instance, opt for ‘proper function’.
Lorenz claims that this definition of kathēkon is as a whole applicable to plants as well as animals and humans. He must, however, immediately face the obstacle of the word prachthen in the cited passage, especially since Alexander of Aphrodisias claims that the Stoics reserved prattein for rational actors and used energein for other living things (De fato34 = SVF 2.1002, cited on p. 60). Lorenz argues, however, that the Stoics might, like Aristotle, have used prattein in both a narrower and a wider sense, i.e., of human actions alone in ethical contexts but in a wider sense of actions of all living things in biological contexts. Lorenz documents this semantic system for Aristotle (pp. 65-70), but admits that the material is too sparse to establish a corresponding Stoic dichotomy (p. 66).
prattein and its Latin equivalents agere and facere are among the commonest verbs in the two languages and are used in various contexts and with various objects. It seems doubtful that prachthen at DL 7.107 fits into the kind of Peripatetic ‘praxis-Begriff’ that Lorenz reconstructs. The instances that Lorenz cites for the ‘broader’ usage in the Stoa (p. 64 nn. 11-12) pertain to human infants and animals, not to plants. This fact suggests that Alexander of Aphrodisias may have overgeneralized (or drawn the dividing line in the wrong place), but it does not help Lorenz’s inclusion of plants. The Stoics, unlike Aristotle (De an. 413a25 ff.), denied a soul to plants (cf. SVF 2.708-10; also in the passage of Hierocles cited below); hence their distinction between zōia and phyta (SVF 1.497; DL 7.107; similarly Cicero, ND 2.120-1). The argument in Stoic physics about the connection between possession of a soul and self-movement (cf. ND 2.32) may also be relevant to the question whether, for the Stoics, a plant could be the subject of prattein. Therefore even though Aristotle spoke of the praxeis of plants, it is open to doubt that a Stoic would have done so.
With respect to the next major point in Diogenes’ definition, the eulogos apologismos (‘reasonable explanation’ or ‘defence’), Lorenz faces the similar problem that the definition would seem to be tailored to human behavior, and he adopts a similar approach, invoking Aristotle’s use of eulogos. But eulogos was used by a variety of authors, including Thucydides, Hippocrates, Aristophanes, Plato, et al. (cf. LSJ s.v.). There is no reason to suppose that the word’s appearance in the Stoic definition of kathēkon had a particular relation to Aristotelian usage.
Lorenz also discusses the tense of prachthen, arguing that the underlying situation is that of an observer of nature, who, once an act has been performed, can assess whether it is in accord with the purpose of the organism’s constitution and hence a kathēkon (pp. 109-10). I suspect, rather, that the situation assumed is that of an individual asked to justify or render an account of his/her actions, perhaps a more plausible scenario than the activity of a scientific observer in view of the fact that apologismos is related to apologizomai ‘render an account’. An accounting procedure for retiring magistrates such as existed in Classical Athens could have provided the model. In addition, the ‘reasonable justification’ receives color from hosa logos hairei poiein (‘all the things reason chooses to do’) with examples pertaining to human actions (to honour one’s parents, siblings, homeland, etc.) later in the DL passage.
One other piece of evidence may be relevant here. In an excerpt from Hierocles, On Marriage, preserved at Stobaeus, Ecl.4, 502.20-503.10 Hense (cited and discussed by Lorenz, pp. 175-6), a distinction is drawn between the kathēkonta of plants, animals and humans. Here the point is made that plants achieve kathēkonta by nature alone, not by selection and calculation (eklogismōi kai arithmēsei) and not by selection from things that are tested (tōn basanizomenōn eklogais). It looks as though the kathēkonta of plants are being defined negatively against those of humans, i.e., that humans do achieve kathēkonta by selection and calculation and selection from things that are tested. This surely is what is meant in DL’s definition by providing a reasonable account (eulogos apologismos) of one’s actions, and this applies specifically to human beings, not to plants. It is surprising that Lorenz, quoting this passage in Chapter VI apropos of human kathēkonta, failed to see its implications for the problem he addressed in Chapters II-V.
The Stoics also offered an etymology of kathēkon: apo tou kata tinas hēkein. Again, Lorenz must face the difficulty that this would prima facie apply to humans rather than animals and/or plants, since tinas, the masc./fem. indefinite pronoun, is regularly rendered ‘certain persons’ or the like. I would translate the phrase ‘from having come after certain persons’ (cf. LSJ s.v. kata B.III.2, providing parallels for its use with a verb of motion), i.e., the kathēkon seeks out, as it were, persons who play certain social roles (and therefore are expected to fulfill certain functions in society, perhaps an early adumbration of the Stoic theory of four human personae famously expounded at Cicero, Off. 1.105-15). Lorenz, on the other hand, again seeks help from Aristotelian usage, but can merely cite instances in which Aristotle uses kathēkon in scientific contexts of the ‘appropriate’ time for certain things to occur as well as the similar usage by Cleanthes at SVF 1.497. He admits in the end that he can arrive at no satisfying explanation (p. 124).
For those unconvinced by Lorenz’s reading of the Stoic kathēkon through an Aristotelian prism, there is an alternative. One can take the beginning of the definition at DL 7.107 through apologismon to have been framed with reference to human behaviour. It was then spliced by our sources together with to akolouthon en zōēi, a more inclusive version of the definition, with en zōēi, rather than en biōi in the version of the definition specific to humans (SVF 3.494, from Stobaeus). Lorenz acknowledges that the Stoics offered both human-specific and more generalized versions of kathēkon; it should not be surprising if our sources have failed to grasp the distinction and keep the two clearly separate.
Lorenz’s last two chapters (V-VI), respectively on further characteristics of the kathēkon and the kathēkon as applied to human beings, should be uncontroversial. Here he considers such questions as the relation of impulse (hormē) to the kathēkon and the sage as arbiter of kathēkonta and the limits on that figure’s competence to judge. Here he relies a good deal on the work of Tad Brennan, especially Brennan 1996.
One has the feeling that this book may have been brought to completion hastily. In Chapter VI one notices a number of items cited that are omitted from the bibliography, mistakes in quoting Greek and Latin, etc. And the volume lacks an index. Above all, Lorenz might have benefited from reconsidering his earlier argument in light of the material discussed at the end (see above). All in all, a mixed performance, which will perhaps be most useful as a summary of the status quaestionis on the human kathēkon in Chapter VI.
Annas, J. 1993. The Morality of Happiness. Oxford.
Brennan, T. 1996. ‘Reasonable Impressions in Stoicism’, Phronesis 41: 318-34.
Brunner, A. 2010. Totas paginas commovere? Cicero’s Presentation of Stoic Ethics in De Finibus Book III. Budapest.
Harrison, A. R. W. 1971. The Law of Athens: Procedure. Oxford.
Kühner, R. and B. Gerth. 1898. Ausführliche Grammatik der griechischen Sprache: Satzlehre. Vol.1. 3rd ed. Hannover-Leipzig.
Long, A. A. and D. N. Sedley. 1987. The Hellenistic Philosophers. Vol. 1. Cambridge.
Schmitz, P. 2014. ‘Cato Peripateticus’ — stoische und peripatetische Ethik im Dialog Cic. ‘Fin.’ 3 und der Aristotelismus des ersten Jh. v. Chr. (Xenarchos, Boethos und ‘Areios Didymos’). Berlin-Boston.
 Lorenz cites (p. 24 n, 14; cf. 133 n. 11) without criticism Brunner 2010: 304, who writes: ‘I do not see any reason to think that Cicero ever encountered and studied Stoic ethics independently’ (sc. of Antiochus of Ascalon). But this is a mere caricature: Brunner seems to lose sight of Cicero’s testimonies about his education with Posidonius and reading of Panaetius, Posidonius, etc.; cf. ND 1.6 and Off. 1.7, 3.8, etc.
 For details see Harrison 1971: 28-31.
 Lorenz, p. 93, sees this possible difficulty but argues that this material belongs to the exposition of human kathēkonta and not the general definition. But that begs the question whether the general definition itself (through apologismon) is tailored to the human being; see below.
 Cf. also Cicero, Off. 1.59, where he speaks of being ‘good calculators (or accountants) of duties’ (ratiocinatores officiorum) as the goal of (human) moral agents.
 Lorenz, p. 119, claims that the choice of the masculine pronoun is possible when a group of objects of various genders is in question; but since the group consists, according to him, of phyta, zōa, and anthrōpoi, one would expect the neuter to be used as the predominant gender; cf. Kühner and Gerth 1898, §370γ.
 There can, by the way, be no question of the word being used here with a double meaning (‘Doppelbedeutung’), i.e. pertaining to both ethics and natural philosophy, as Lorenz claims (p. 123).