---
slug: deontic_modality
name: Deontic Modality
one_liner: "The modal status of actions or states under a normative system — classifying them as obligatory, permitted, forbidden, or optional — with an anatomy that mirrors alethic possibility/necessity but ranges over norms rather than truth."
type: prime
schema_version: 2
status: density_v2_draft
categories: [structural, social, computational]
origin_domain: logic
alternate_origin_domains: [law, ethics, artificial_intelligence, game_design]
aliases: [deontic_logic, obligation_permission_prohibition, normative_modality, deontic_status, obligatory_permitted_forbidden]
related: []
solution_archetypes: []
review_flags:
- "OPERATOR-DERIVED (op-06 modalization, flavor 6c mandatory→default) — the modal-structure prime obtained by lifting the normative from a flat fact to a modal classification of actions/states as OBLIGATORY / PERMITTED / FORBIDDEN / OPTIONAL under a norm system, mirroring alethic necessary/possible over norms rather than truth. Surfaced from `taboo` and the 6c normative cluster. Discovered 2026-07-03. MODERATE hold (verified absent from corpus; established named construct — von Wright 1951, deontic logic). STATUS: HOLD pending owner keep/cut."
- "Created 2026-07-03; STUB ONLY (frontmatter + Core Idea + Notes). SI/SF/similarity are PROPOSER ESTIMATES pending triangulation. Body sections (Structural Signature onward) NOT written."
- "Phase-C action: re-similarity-check vs `normativity` (the genus of the normative — deontic_modality is its MODAL CLASSIFICATION structure, not the broad phenomenon), `mandatory_vs_default_norms` (one axis WITHIN deontic space), and `possibility` (a separate op-06 stub — deontic_modality is the deontic analog of alethic possibility; note the alethic/deontic modal pair and cross-reference it); confirm it is a genuine distinct modal structure and not a restatement of `normativity`; draw a structure-of edge normativity→deontic_modality + an edge to mandatory_vs_default_norms + a deontic-analog-of cross-reference to `possibility`; write a v1 draft and sync the one_liner across v1/v2 per CLAUDE.md before merge."
substrate_independence:
  composite_substrate_independence: 4
  domain_breadth: 5
  structural_abstraction: 3
  transfer_evidence: 4
  reasoning: 'The bare structure — a four-way modal classification of actions/states under a norm system (obligatory = "necessary" under the norms, forbidden = "impossible" under the norms, permitted = "possible", optional = indifferent), closed under the duality obligatory-to-do = forbidden-to-omit and organized by a deontic square of opposition — is a genuinely substrate-neutral modal form that recurs wherever any normative system classifies moves. It appears in law (duties, rights, powers, permissions), ethics (moral obligation/permission/prohibition), normative multi-agent AI and machine ethics (permitted vs. forbidden agent actions), social norms and taboo, game design (legal vs. illegal moves), and access-control / protocol design (permitted operations). These are structurally-unlike siblings sharing only the abstract modal-classification engine, so domain_breadth scores 5. Structural abstraction is 3 rather than higher because, although the obligatory/permitted/forbidden lattice and its duality are pure structure, the core still leans on the vocabulary of "norm," which imports a mild evaluative/institutional cast that keeps it just short of a fully substrate-free statement. Transfer evidence is strong (deontic logic is a canonical, independently formalized construct across logic, jurisprudence, ethics, and AI).'
similarity_to_nearest_existing_prime:
  slug: normativity
  similarity: 0.62
structural_framed:
  label: mixed
  aggregate: 0.4
  criteria: {vocab_travels: 0.6, evaluative_weight: 0.5, institutional_origin: 0.3, human_practice_bound: 0.3, import_vs_recognize: 0.4}
  rationale: 'Reads structural-to-mixed. The obligatory/permitted/forbidden/optional classification, its duality (obligatory-to-do = forbidden-to-omit), and the deontic square are recognized as a modal structure rather than imported wholesale, and they travel cleanly into game rules, access-control, and normative AI without carrying legal or ethical substance. The frame residue is moderate: the "norm" vocabulary imports some evaluative and institutional cast (keeping evaluative_weight and institutional_origin off the floor), because unlike alethic modality the modal source here is a standard that licenses praise/blame rather than a fact about truth. On balance the underlying second structure — a modal classification of actions parallel to necessity/possibility but over norms — is substrate-neutral, placing it mixed and lower-framed than surrounding framed-stratum candidates.'
phase_b_passes_completed: []
---
# Deontic Modality

## Core Idea

Deontic modality is the *modal status of actions and states under a normative system*: the classification of a move as OBLIGATORY (required — forbidden to omit), PERMITTED (allowed), FORBIDDEN (prohibited — obligatory to omit), or OPTIONAL/indifferent (neither required nor barred). It is reached by lifting the normative from a flat fact ("this norm holds") to a *modal classification* of the whole action space — the same lift that takes truth-about-a-fact up to alethic modality (necessary/possible), but performed over norms instead of truth. Where alethic modality asks whether a proposition *must* or *may* be true, deontic modality asks whether an action *must* or *may* be done under the governing norms.

The load-bearing anatomy is an isomorphism with alethic modality that runs one level up over norms rather than over truth. *Obligatory* is the deontic analog of *necessary*: what the norms require, and what it is forbidden to omit. *Forbidden* is the analog of *impossible*: what the norms exclude, and what it is obligatory to omit. *Permitted* is the analog of *possible*: what the norms allow. This yields the deontic duality — obligatory-to-do is exactly forbidden-to-omit, permitted-to-do is exactly not-obligatory-to-omit — and a deontic square of opposition mirroring the modal square. The feature that makes this a distinct structure rather than a mere restatement of "there is a norm" is precisely the modal classification of the *action space as a whole*: every action acquires a status, the statuses are inter-definable through negation and omission, and the source of the modality is a normative standard rather than a fact about what is the case.

Read structurally, the same obligatory/permitted/forbidden shape appears wherever a normative system classifies moves, and the siblings are genuinely unlike. In *law*, deontic modality is the space of legal modalities — duties, permissions, prohibitions, and the powers that generate them. In *ethics*, it is the classification of acts as morally required, permissible, or wrong. In *normative multi-agent AI and machine ethics*, it is the explicit tagging of agent actions as permitted or forbidden under an operative norm set. In *game design*, it is the partition of moves into legal and illegal; in *access-control and protocol design*, the partition of operations into permitted and denied. Across these, the shared abstract engine is a modal classification of actions under a norm — the obligatory/permitted/forbidden lattice with its duality — and the legal or ethical case is one species of the genus, with the structurally-unlike siblings showing the genus is the bare deontic-modal structure.

## Notes

**Provenance.** Produced by operator 06 (modalization), flavor 6c (mandatory→default), as the modal-structure prime obtained by lifting the normative from a flat fact to a modal classification of the action space — the obligatory/permitted/forbidden/optional status of actions under a norm system. Surfaced from `taboo` and the 6c normative cluster on 2026-07-03. Established named construct: deontic logic, von Wright 1951 ("Deontic Logic", *Mind*), the obligation/permission/prohibition classification and its square of opposition. Claimed siblings: legal modalities (duties/rights/powers) in law, moral obligation/permission/prohibition in ethics, permitted-vs-forbidden agent actions in normative multi-agent AI and machine ethics, legal/illegal moves in game design, and permitted operations in access-control/protocol design. Verified absent from the corpus. Manifest: MODERATE hold.

**For owner evaluation (keep/cut).** The case FOR: deontic modality is a *canonical, named construct* (deontic logic — not a proposer coinage), verified absent, with a clean modal anatomy — the obligatory/permitted/forbidden/optional lattice, the duality (obligatory-to-do = forbidden-to-omit), and the deontic square — that parallels alethic modality over norms rather than truth, and that the corpus's existing normative primes do not name as such. The RISKS Kurt should weigh: (1) **overlap with `normativity`** — the discriminating claim is that deontic_modality is the specific MODAL CLASSIFICATION structure (the four-way obligatory/permitted/forbidden/optional partition with its duality), whereas `normativity` is the broader phenomenon of standards licensing praise and blame; deontic_modality is the *modal shape of* the normative, not the normative itself. (2) **overlap with `mandatory_vs_default_norms`** — that prime names one *axis within* deontic space (the mandatory/default contrast), a special case rather than the whole classification, so it should attach as a component, not merge. (3) **Whether it should be evaluated together with the `possibility` stub as the alethic/deontic modal pair** — deontic_modality is the deontic analog of alethic possibility/necessity, and Kurt may wish to adjudicate the two stubs jointly to fix the parallel and avoid double-naming the shared modal skeleton. Sharp keep/cut question: *is "the obligatory/permitted/forbidden classification of actions" a distinct prime, or is it just `normativity` restated?* — the proposer's answer is that the modal classification of the action space, with its duality and square, is a level-up structure the flat `normativity` phenomenon does not name.

**At incorporation.** Re-run similarity against `normativity` (nearest genus — the broad normative phenomenon), `mandatory_vs_default_norms` (one axis within deontic space), and `possibility` (the separate op-06 alethic-modal stub — screen for the alethic/deontic parallel and cross-reference) to confirm no collapse. If kept: draw a structure-of edge `normativity` → `deontic_modality` (deontic_modality is the modal classification structure of the normative), a composition/specialization edge relating `mandatory_vs_default_norms` (an axis within) to `deontic_modality`, and a deontic-analog-of cross-reference to `possibility` marking the alethic/deontic modal pair. Add a missing-edge note flagging the `normativity` structure-of relationship and the `possibility` modal-pair contrast explicitly. Write a v1 draft and sync the one_liner across v1 and v2 per CLAUDE.md before merge.
