Bar-Lev (2021): An Implicature Account of Homogeneity and Non-Maximality #
@cite{bar-lev-2021}
An Implicature Account of Homogeneity and Non-Maximality. Linguistics and Philosophy 44:1045–1097.
Core Contribution #
Bar-Lev derives homogeneity, universality, and non-maximality for plural definites from a single mechanism: exhaustification with subdomain alternatives via the Exh^{IE+II} operator of @cite{bar-lev-fox-2020}.
The key ingredients:
∃-PL (existential pluralization): The basic meaning of a plural definite like "the kids laughed" is existential: at least one kid laughed. This operator is defined in
ExistentialPL.lean.Subdomain alternatives: Replacing the domain variable D with subsets D' ⊆ D generates alternatives that are NOT closed under conjunction — structurally parallel to free choice disjunction (@cite{fox-2007}).
Exh^{IE+II}: The same exhaustivity operator that derives free choice from ◇(A ∨ B) derives universality from ∃-PL. Since the subdomain alternatives are not closed under ∧, no non-prejacent alternative is innocently excludable, and all are innocently includable.
Structural Parallel with Free Choice #
This file proves that the Exh^{IE+II} derivation for homogeneity is
structurally isomorphic to the free choice derivation in
Phenomena/Modality/Studies/BarLevFox2020.lean:
| Free Choice | Homogeneity |
|---|---|
| FCWorld (5 worlds) | HomWorld (4 worlds) |
| ◇(A ∨ B) (prejacent) | someLaughed (∃-PL) |
| {◇(A∨B), ◇A, ◇B, ◇(A∧B)} | {someLaughed, kellyL, janeL} |
| ◇A ∧ ◇B ∉ ALT | kellyL ∧ janeL ∉ ALT |
| IE = {◇(A∧B)} | IE = ∅ |
| II = {◇A, ◇B} | II = {kellyL, janeL} |
| Free choice | Universal reading |
Asymmetry of Positive and Negative #
A key prediction: the positive and negative cases are not symmetric.
- Positive "the kids laughed": existential basic meaning, strengthened to universal by Exh^{IE+II} (implicature).
- Negative "the kids didn't laugh": ¬∃ = ∀¬ from basic semantics alone — no strengthening needed.
This asymmetry is derived in negative_universal below.
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- BarLev2021.instDecidableEqHomWorld x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯
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- One or more equations did not get rendered due to their size.
- BarLev2021.instReprHomWorld.repr BarLev2021.HomWorld.both prec✝ = Repr.addAppParen (Std.Format.nest (if prec✝ ≥ 1024 then 1 else 2) (Std.Format.text "BarLev2021.HomWorld.both")).group prec✝
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- BarLev2021.instReprHomWorld = { reprPrec := BarLev2021.instReprHomWorld.repr }
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- BarLev2021.instInhabitedHomWorld = { default := BarLev2021.instInhabitedHomWorld.default }
Kelly laughed (subdomain alternative for D = {Kelly}).
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Jane laughed (subdomain alternative for D = {Jane}).
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The prejacent: ∃-PL_{D={Kelly,Jane}} P (the kids) = "some kid laughed." This is the basic existential meaning of "the kids laughed."
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Grounding in ExistentialPL.lean #
The propositions above are instances of the existPL operator from
ExistentialPL.lean. We make this connection structural: each proposition
is provably equivalent to existPL applied with the appropriate domain
variable D.
The two atoms of the plurality "the kids".
Instances For
Equations
- BarLev2021.instDecidableEqKid x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯
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- BarLev2021.instReprKid.repr BarLev2021.Kid.kelly prec✝ = Repr.addAppParen (Std.Format.nest (if prec✝ ≥ 1024 then 1 else 2) (Std.Format.text "BarLev2021.Kid.kelly")).group prec✝
- BarLev2021.instReprKid.repr BarLev2021.Kid.jane prec✝ = Repr.addAppParen (Std.Format.nest (if prec✝ ≥ 1024 then 1 else 2) (Std.Format.text "BarLev2021.Kid.jane")).group prec✝
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- BarLev2021.instReprKid = { reprPrec := BarLev2021.instReprKid.repr }
The predicate "laughed" as a function of atoms and worlds.
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- One or more equations did not get rendered due to their size.
The plurality "the kids" = {Kelly, Jane}.
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Grounding: someLaughed is the ∃-PL operator applied with full
domain variable D = theKids.
Grounding: kellyLaughed is ∃-PL with singleton domain D = {Kelly}.
Grounding: janeLaughed is ∃-PL with singleton domain D = {Jane}.
The subdomain alternative set.
Full domain variable D = {Kelly, Jane}. Subdomain alternatives arise from D' ⊆ D:
- D' = {Kelly, Jane}: someLaughed (= prejacent)
- D' = {Kelly}: kellyLaughed
- D' = {Jane}: janeLaughed
- D' = ∅: trivially true (excluded as non-informative)
Crucially, the conjunction kellyLaughed ∧ janeLaughed is NOT in this set — the alternatives are not closed under ∧.
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The prejacent: ∃-PL with full domain.
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The subdomain alternatives are NOT closed under conjunction.
kellyLaughed ∧ janeLaughed (= "both laughed") is not equivalent to any member of homAlt. This is the structural property that enables the Exh^{IE+II} derivation, parallel to free choice.
IE Computation #
For φ = someLaughed and ALT = {someLaughed, kellyLaughed, janeLaughed}:
There are two MC-sets (maximal sets of negated alternatives consistent with the prejacent):
- MC₁ = {φ, janeLaughedᶜ} — witness: onlyKelly
- MC₂ = {φ, kellyLaughedᶜ} — witness: onlyJane
The IE set is {a ∈ ALT : aᶜ ∈ every MC-set}. The intersection MC₁ ∩ MC₂ = {φ}, and since φᶜ is never in an MC-set (contradicts the prejacent), no alternative is innocently excludable.
More precisely: kellyLaughedᶜ ∉ MC₁ and janeLaughedᶜ ∉ MC₂, so neither individual alternative is in IE. And someLaughed = φ cannot be IE-excluded by definition.
This contrasts with free choice, where ◇(A ∧ B) IS IE-excludable. The difference: homAlt has only 3 elements (no conjunction member), while fcALT has 4 (including ◇(A ∧ B)).
Nothing is innocently excludable in the homogeneity configuration.
This is the key difference from free choice, where ◇(A ∧ B) IS IE-excludable. Here, the alternatives lack a conjunction member entirely, so neither individual alternative can be consistently excluded from all MC-sets.
II Computation #
Since IE = ∅ (nothing is excludable), the II constraint set is just {someLaughed} (the prejacent, with no IE negations).
All members of homAlt hold at .both, so adding any target to an II-compatible set R preserves II-compatibility (witness: .both).
Result: II = {kellyLaughed, janeLaughed} (and someLaughed, but the prejacent is already asserted).
kellyLaughed is innocently includable.
janeLaughed is innocently includable.
Universality from Exh^{IE+II}: exhaustified "the kids laughed" entails that both Kelly and Jane laughed.
Exh^{IE+II}(∃-PL_C(laughed)(the kids)) ⊢ ∀ x ∈ {K,J}. laughed(x)
This is the homogeneity derivation: the universal reading of a plural definite arises as an implicature, not from basic semantics.
Compare free_choice in Phenomena/Modality/Studies/BarLevFox2020.lean.
Negative asymmetry: Under negation, the universal reading comes for free from the basic (existential) semantics: ¬∃x. laughed(x) ⊢ ∀x. ¬laughed(x).
No exhaustification needed — this is just the classical equivalence ¬∃ = ∀¬. This asymmetry between positive and negative is a key prediction that distinguishes the implicature account from trivalent theories (where both polarities are symmetric).
In a gap scenario (some but not all laughed), the positive sentence is false (universality fails) and the negative sentence is false (existence holds). This non-complementarity IS the homogeneity gap.
Witness: onlyKelly is a gap scenario.
Witness: onlyJane is a gap scenario.
Non-Maximality via Pruning #
@cite{bar-lev-2021} §5 derives non-maximal readings via pruning: when context makes certain subdomain alternatives irrelevant, they are removed from ALT before exhaustification. With fewer alternatives, Exh^{IE+II} produces a weaker (non-maximal) reading.
The pruning spectrum for a 2-atom plurality {Kelly, Jane}:
| ALT | Result |
|---|---|
| {φ, kellyL, janeL} (full) | Universal (both laughed) |
| {φ, janeL} (kelly pruned) | janeL excluded by IE |
| {φ, kellyL} (jane pruned) | kellyL excluded by IE |
| {φ} (fully pruned) | Existential (some kid laughed) |
Note: with only 2 atoms, partial pruning yields exclusive readings (IE excludes the remaining alternative), not intermediate non-maximal readings. True non-maximality (e.g., "7 of 10 kids laughed" counting as "the kids laughed") requires ≥3 atoms, where pruning some but not all individual alternatives weakens the II result to something between existential and universal.
In the fire hazard context (NonMaximality.lean), the distinction
between "all kids laughed" and "some kids laughed" is irrelevant,
so ALL individual alternatives are pruned. Exh is then vacuous and
the existential basic meaning surfaces directly.
Fully pruned alternative set: only the prejacent remains.
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With a fully pruned alternative set, Exh^{IE+II} reduces to the basic existential meaning (no strengthening occurs).
The converse: the basic meaning suffices for Exh with pruned alternatives.
Pruning strictly weakens the reading: the universal reading (full ALT) entails the existential reading (pruned ALT), but not vice versa.
Partially pruned alternative set: kellyLaughed removed, janeLaughed retained.
With this ALT = {φ, janeLaughed}, there is a single MC-set {φ, janeLaughedᶜ} (witness: onlyKelly). So janeLaughed ∈ IE, and Exh^{IE}(φ) = someLaughed ∧ ¬janeLaughed. The 2-atom case yields exclusive readings under partial pruning, not weakened universals. True non-maximal readings require ≥3 atoms.
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Partial pruning (removing kellyLaughed) does not yield universality.
Counterexample: .onlyKelly satisfies Exh^{IE+II} (janeLaughed is IE-excluded and someLaughed is II-included) but not the universal kellyLaughed ∧ janeLaughed.
Bar-Lev's theory predicts the full truth-value pattern for the
switches example: universal in ALL, denial in NONE, gap in between.
This matches the empirical judgments in Homogeneity.lean.
Bar-Lev's theory is an implicature account: any theory using the SI mechanism for multiplicity is uniquely identified as the implicature theory. Bar-Lev's exhaustification-based approach is precisely this.
Comparison with @cite{magri-2014} #
Both Magri and Bar-Lev derive universality from exhaustification of an existential basic meaning. The key differences:
Magri: Uses double exhaustification (EXH(EXH(THE))) with non-transitive Horn-mateness to block THE from excluding ALL directly.
Bar-Lev: Uses single Exh^{IE+II} with subdomain alternatives. The key insight is that subdomain alternatives are not closed under ∧, which is what triggers II (Innocent Inclusion).
Bar-Lev's approach is more economical (one application of Exh, not two) and unifies homogeneity with free choice through a shared structural property (non-closure under ∧).
Both theories agree that the basic meaning is existential and the strengthened meaning is universal. The key structural difference: Magri requires two applications of EXH (double exhaustification via non-transitive Horn-mateness), while Bar-Lev requires one application of Exh^{IE+II} (the richer operator compensates for fewer iterations). Bar-Lev's approach also unifies homogeneity with free choice through the shared structural property of non-closure under ∧.
How "All" Removes Homogeneity #
@cite{bar-lev-2021} §8.3: "all the kids laughed" does not display
homogeneity because all universally quantifies over the plurality,
eliminating the domain variable D. Without D, there are no subdomain
alternatives, so Exh^{IE+II} is vacuous — the universal reading is
the basic meaning, not an implicature. Since it's not an implicature,
it can't be weakened by pruning, which is why "all" blocks
non-maximality.
This connects to Homogeneity.lean's HomogeneityRemover.all and to
@cite{kriz-2016}'s removeGap (which collapses the truth-value gap
into the negative extension — a different mechanism but the same
empirical prediction).
Bar-Lev's theory predicts that "all" removes homogeneity: the
allRemovesHomogeneity datum records that the gap scenario yields
.clearlyFalse for "all the doors are open" (vs .neitherTrueNorFalse
for the bare plural). This aligns with Bar-Lev's mechanism: "all"
eliminates subdomain alternatives, making the universal reading
semantic (not an implicature) and therefore non-cancelable.
Without subdomain alternatives, exhaustification is vacuous:
the prejacent passes through unchanged. This models the effect
of all, which eliminates the domain variable D.
Comparison with @cite{kriz-2016} (Trivalent Account) #
@cite{kriz-2016} and @cite{kriz-spector-2021} derive homogeneity from trivalent semantics: plural predication yields a three-valued denotation (true/false/gap), and non-maximality arises when the gap is pragmatically exploitable. The two accounts differ in:
| Property | Bar-Lev (implicature) | Križ (trivalent) |
|---|---|---|
| Basic meaning | existential (∃-PL) | trivalent (T/F/gap) |
| Universal reading | implicature (Exh^{IE+II}) | semantic (true extension) |
| Non-maximality | pruning alternatives | pragmatic gap exploitation |
| Positive/negative | asymmetric | symmetric |
| "All" removes gap | eliminates C variable | collapses gap (removeGap) |
Key Distinguishing Prediction: Asymmetry #
The most important empirical difference concerns the status of the universal inference under negation:
Bar-Lev: Positive universality is an implicature (cancelable via pruning). Negative universality is semantic (¬∃ = ∀¬, no implicature involved). The two polarities are fundamentally asymmetric.
Križ: Both positive and negative universality arise from the same source (gap collapse). The gap is symmetric: it exists for both "the kids laughed" and "the kids didn't laugh." Non-maximality is available for both polarities.
This asymmetry is captured by negative_universal above: under
negation, the universal reading follows from basic semantics without
exhaustification. Križ's trivalent account would instead derive both
through the gap mechanism symmetrically.
The positive–negative asymmetry: positive universality requires exhaustification, while negative universality does not.
This is a distinguishing prediction of the implicature account:
universality needs the full Exh^{IE+II} machinery, but
negative_universal is a simple logical entailment. In the trivalent
account (@cite{kriz-2016}), both arise from the gap structure.
The §11 prose comparison is upgraded here to a kernel-checked divergence
theorem: lift the BarLev Set HomWorld predicates into Bool-valued versions,
instantiate Križ's barePluralTV over them, and demonstrate that at the
gap-world onlyKelly:
- Križ's bare-plural is
.indet(gap), and its Strong-Kleene negation is ALSO.indet(gap). So Križ'sgap_enables_nonmaxmakes non-maximal use of the negation available in principle. - Bar-Lev's
negative_universal(above) makes¬someLaughedstraightforwardly bivalent — atonlyKellyit's FALSE (since some kid did laugh). No gap to exploit, so non-maximal use of negation is forbidden.
The two predictions cannot both be right: this is the kernel-visible form of the §11 polarities-symmetric vs. polarities-asymmetric disagreement.
At onlyKelly, Križ's bare-plural denotation of "the kids laughed" is
a homogeneity gap (.indet) — Kelly laughed, Jane didn't.
Križ's Strong-Kleene negation of a gap is also a gap. So the negation
"the kids didn't laugh" at onlyKelly is .indet under Križ.
Bar-Lev's negative_universal derives ¬someLaughed as bivalent:
at onlyKelly, ¬someLaughed .onlyKelly is FALSE (Kelly laughed).
Križ vs. Bar-Lev formal divergence on negative non-maximality.
At the gap-world onlyKelly:
- Križ: negation of "the kids laughed" is
.indet(Strong-Kleene preserves the gap). Sogap_enables_nonmaxmakes non-maximal use of the negation in principle available — symmetric with the positive. - Bar-Lev:
¬someLaughedis straightforwardly bivalent (¬∃ = ∀¬). AtonlyKelly,¬someLaughedis FALSE — no gap to exploit. The negation cannot be used non-maximally — asymmetric with positive.
The two clauses below cannot both be the right semantics for "the kids
didn't laugh" at onlyKelly. The theorem's existence packages the
formal disagreement that §11 §positive_negative_asymmetry describes
in prose.