Documentation

Linglib.Features.Accessibility

Accessibility — Ariel's referential-form scale #

AccessibilityLevel: a fine-grained (18-tier) reconstruction of [Ari01]'s Accessibility Marking Scale (least accessible fullNameMod to most accessible zero), with rank, the coarsening toDefLevel to Prominence.DefinitenessLevel, and the GHZ bridge GivennessStatus.toAccessibility. The tier order follows Ariel; the verbalAgreement/zero split refines her single "Extremely High Accessibility Markers" tier.

Accessibility and definiteness are non-monotonically related (full names are less accessible than definite descriptions, yet first/last names are more accessible; names are also more prominent for DOM), so they are separate types and toDefLevel is many-to-one and non-monotone.

Sibling of Features/Givenness.lean (GHZ-6): this classifies forms, GivennessStatus classifies entities. Also here: NextMentionBias and a typicalWeight NP-weight correlate ([AWLG00]).

Accessibility marking scale #

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inductive Features.AccessibilityLevel :
Type

[Ari01]'s Accessibility Marking Scale: a fine-grained ordering of referential form types from least to most accessible.

Each constructor represents a class of referring expressions. Speakers use more reduced forms for more accessible referents.

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    @[implicit_reducible]
    instance Features.instDecidableEqAccessibilityLevel :
    DecidableEq AccessibilityLevel
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    def Features.instReprAccessibilityLevel.repr :
    AccessibilityLevel → ℕ → Std.Format
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      @[implicit_reducible]
      instance Features.instReprAccessibilityLevel :
      Repr AccessibilityLevel
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      @[implicit_reducible]
      instance Features.instFintypeAccessibilityLevel :
      Fintype AccessibilityLevel
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      @[implicit_reducible]
      instance Features.instInhabitedAccessibilityLevel :
      Inhabited AccessibilityLevel
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      def Features.AccessibilityLevel.rank :
      AccessibilityLevel → ℕ

      Numeric rank: 0 (lowest accessibility) to 17 (highest). Higher rank = higher accessibility = more reduced form.

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        def Features.AccessibilityLevel.toDefLevel :
        AccessibilityLevel → Prominence.DefinitenessLevel

        Coarsening: each accessibility level maps to one of the 5 DefinitenessLevel categories used for differential argument marking. This is a many-to-one, non-monotone mapping — names are less accessible than definite descriptions but more prominent for DOM.

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          theorem Features.pronoun_more_reduced_than_name :
          AccessibilityLevel.unstressedPron.rank > AccessibilityLevel.fullName.rank

          An unstressed pronoun is more reduced than a full name.

          Next-mention bias #

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          inductive Features.NextMentionBias :
          Type

          Next-mention bias: how likely a discourse referent is to be mentioned again in the subsequent utterance. Driven by thematic roles, coherence relations, and discourse structure.

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            @[implicit_reducible]
            instance Features.instDecidableEqNextMentionBias :
            DecidableEq NextMentionBias
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            def Features.instReprNextMentionBias.repr :
            NextMentionBias → ℕ → Std.Format
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              @[implicit_reducible]
              instance Features.instReprNextMentionBias :
              Repr NextMentionBias
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              def Features.NextMentionBias.predictedForm :
              NextMentionBias → AccessibilityLevel

              Accessibility prediction: high next-mention bias licenses reduced referential form (unstressed pronoun); low bias requires full form (full name).

              This is the monotone link at the heart of [Ari01]'s Accessibility Marking Scale: more accessible referents → more reduced forms. The same relationship underlies the Probabilistic Reduction Hypothesis (more predictable → shorter/more reduced).

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                theorem Features.high_bias_more_reduced :
                NextMentionBias.high.predictedForm.rank > NextMentionBias.low.predictedForm.rank

                The predicted form for high-bias referents is more reduced than for low-bias referents.

                Weight bridge #

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                def Features.AccessibilityLevel.typicalWeight :
                AccessibilityLevel → ℕ

                NP weight correlate: reduced referential forms are lighter. Approximate number of words in a typical instance of each form. This connects form selection to constituent ordering (heavy NP shift, DLM).

                The same choice that makes a referent "more reduced" also makes it "lighter", linking [Ari01]'s accessibility hierarchy to [AWLG00]'s heaviness effects.

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                  theorem Features.pronoun_lightest :
                  AccessibilityLevel.unstressedPron.typicalWeight ≤ AccessibilityLevel.shortDefDescription.typicalWeight

                  Pronouns are at most as heavy as definite descriptions.

                  Givenness projection #

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                  def Features.GivennessStatus.toAccessibility :
                  GivennessStatus → AccessibilityLevel

                  Ariel's GHZ→AccessibilityLevel projection ([Ari01]): the prototypical accessibility level for each givenness status.

                  Caveat: GHZ's lower statuses (referential = "indefinite this N", typeIdentifiable = "a N") are indefinite, which do not appear on Ariel's accessibility-marking scale (Given/definite forms); the mapping for these two is by approximate accessibility degree, not by form identity.

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