Nomos and Phusis (Convention vs Nature)

The great fifth-century antithesis between convention/law (nomos) and nature (phusis) — is justice a real feature of the world or a human contrivance? — staged across three Platonic dialogues, most radically by Callicles in the Gorgias. Callicles is a phusis-normativist: conventional justice is "a contrivance of the weak and the many… with their own advantage in mind" (483b) to fetter the strong, but by nature "the superior rule the inferior and have a greater share" (pleonexia, 483d) — so to follow nature is to take more. Against this the Protagoras' Great Speech makes civic virtue conventional but universal (Zeus's gift of aidōs and dikē "to all"), and the Republic's Glaucon gives the social-contract genesis of justice as a nomos the weak covenant to. Plato's reply, in each case, is that nomos rightly understood is not against nature but expresses the soul's real good.

Key Points

Callicles' nature-justice (Gorgias 482c–484c): law is the many's fraud against the strong; nature shows "everywhere" — animals, cities, Xerxes' campaign — that the better rule and have more. Pleonexia (getting-more) is natural right, not vice.
The "stronger/better/superior" slide: Socrates' diagnostic that Callicles cannot fix the referent of kreittōn — the many are collectively stronger, so "the laws of the many" are the laws of the superior, collapsing nature-justice back into convention (488b–489b).
Protagoras' inversion: in the Great Speech, nomos (civic virtue) is not natural endowment but a gift distributed to all and cultivated by teaching/punishment — convention as what saves the species, not what fetters the strong (Protagoras 320c–328c).
Glaucon's social contract (Republic 358e–359b): justice is a nomos, a "mean" the weak agree to, "neither… doing injustice with impunity nor suffering it" — the conventionalist challenge the whole Republic answers.
The Sophistic background: nomos/phusis is the Sophistic antithesis; Plato dramatizes its immoralist (Callicles), its humanist (Protagoras), and its contractarian (Glaucon) versions, then argues each misreads what nomos is for.
The Crito's endorsed (vertical) contract (50a–54d): the personified Laws of Athens voice a vertical citizen↔city contract — obey-or-persuade, the city-as-parent — that Socrates accepts. This is the structural inverse of Glaucon's horizontal contract-of-the-weak (which Plato refutes): the same "social contract" label, opposite valence (endorsed obligation vs. debunking genesis). A standing false-friend — do not conflate, and do not assimilate either to the modern Hobbes/Rousseau horizontal contract.
The Laws' metaphysical reply (Book X): where the Gorgias/Republic answer the conventionalist on ethical-psychological grounds, the Laws attacks the cosmology beneath him — by proving soul prior to body, it makes reason, law, and justice "preeminently natural," so that rightly-grounded nomos governing willing subjects "is not unnatural" (690c). Nomos properly understood just is phusis.
The Minos' barest collapse (a dubium): the Minos identifies true law itself with tou ontos exeuresis — "the discovery of reality" (315a) — so genuine nomos just is the grasp of an unchanging common reality, and the variability of nomoi (Carthaginian child-sacrifice, changed burial rites) is reclassified as failure to discover, not as evidence of conventionality (315b–c). A third, barer answer to the conventionalist than the Gorgias/Republic ethical reply or the Laws X metaphysical one — though its disputed authorship keeps it corroborating, not anchoring. See claims#plato-minos-supplies-the-laws-missing-definition-of-law (live claim).

What the Concept Does

Frames the foundational question of political philosophy — whether justice has a ground in the nature of things or is a human institution serving someone's interest; the answer fixes whether one ought to be just when one can get away with injustice.
Lets Plato separate three distinct theses that "convention" can name — fraud-on-the-strong (Callicles), species-saving gift (Protagoras), contract-of-the-weak (Glaucon) — and answer each differently.
Turns the immoralist's own appeal to nature against him — by showing the "stronger" is whoever actually rules (often the many), so "nature" cannot underwrite the strong individual's license.

What It Rejects

The reduction of justice to the interest of the powerful — whether in Callicles' phusis form or the cynical-conventionalist form of Thrasymachus.
The equation of nature with appetite-maximization — Callicles' picture of the natural life as the unchecked filling of ever-larger appetites, answered by the Gorgias' ordered soul and the leaky-jar image.

Stakes

Nomos/phusis is where the corpus's two "advantage of the stronger" immoralists are best distinguished. Callicles (Gorgias) grounds his immoralism in phusis: the strong ought by nature to rule and take more, so convention is a fraud against nature. Thrasymachus (Republic I) is closer to a cynical conventionalist: justice just is the established interest of whatever power rules. Callicles is the more radical and candid — he says aloud what nomos exists to suppress ("others are thinking but are unwilling to say," 492d) — which is exactly why he, not Thrasymachus, is the harder case the Republic is built to answer. See claims#callicles-thrasymachus-two-immoralisms (candidate).

Connections

is the axis distinguishing callicles from Thrasymachus — phusis-normativism vs. cynical conventionalism. See claims#callicles-thrasymachus-two-immoralisms (candidate).
is answered by the ordered soul — the Gorgias' reply that the good is the due, not the maximal, share; pleonexia is disease, not health.
is inverted by the Great Speech — civic virtue as a universal conventional gift that saves the species, not a natural license for the strong.
sets the challenge for plato-republic — Glaucon's social-contract genesis of justice as nomos is the conventionalist position the Republic must defeat.
contrasts with theory-of-forms — if there is a Form of the Just, justice is grounded in phusis in a sense neither Callicles nor the contractarians allow (the just-itself, not the strong's advantage).
is inverted by the Laws — Book X grounds nomos in the priority of soul, so rightly-ordered law is "not unnatural" (690c): convention rightly understood is nature.
is collapsed most directly by the Minos — true law identified with "the discovery of reality" (315a), so genuine nomos just is the grasp of being and the antithesis dissolves at its barest; a dubium, so corroborating not anchoring (see claims#plato-minos-supplies-the-laws-missing-definition-of-law, candidate).
is given an endorsed (vertical) form by plato-crito — the Laws-of-Athens contract Socrates accepts, the structural inverse of Glaucon's debunking horizontal contract-of-the-weak.

Open Questions

Does Plato have a positive account of natural justice (justice grounded in the soul's real structure / the Forms), or only a refutation of the immoralist's phusis? The Republic's soul-justice is the candidate answer.
Is the historical Sophistic nomos/phusis debate (Antiphon, the Dissoi Logoi) reported faithfully by Plato, or reshaped to be refuted? The wiki has no Sophist primary sources to check against (a source gap).
How does the Protagoras' "conventional but universal and teachable" virtue relate to the Gorgias' rejection of convention-as-fraud — two compatible halves, or a tension?

Sources

plato-gorgias — Callicles' nomos/phusis immoralism, pleonexia, and the "stronger" slide (482c–491d).
plato-protagoras — the Great Speech: civic virtue as a universal, teachable, conventional gift (320c–328c).
plato-republic — Glaucon's social-contract genesis of justice as nomos (358e–359b); Thrasymachus' "advantage of the stronger" (338c).
plato-crito — the personified Laws of Athens; the vertical (citizen↔city) social contract Socrates endorses (50a–54d).
plato-laws — the metaphysical reply: soul prior to body makes nomos preeminently natural (Book X; 690c, 889e).
plato-minos — true law as tou ontos exeuresis ("the discovery of reality," 315a); the variability of laws as failure-to-discover (315b–c). A dubium.