Syntactic Ambiguity: Temporary Ambiguity and Garden-Path Effects

Temporary syntactic ambiguity arises when an initial substring of a sentence is compatible with multiple structural analyses. The parser must commit to one analysis before the disambiguating material arrives. When the initial commitment turns out to be incorrect, a garden-path effect results: the reader experiences processing difficulty at the point of disambiguation, often visible as longer reading times and/or regressive eye movements.

CC/RC Ambiguity

The best-studied case is the complement clause (CC) vs. relative clause (RC) ambiguity in English (@cite{altmann-garnham-dennis-1992}):

• He told the woman that he'd risked his life for many people ... (CC)
• He told the woman that he'd risked his life for to install ... (RC)

The substring the woman that he'd risked his life for is temporarily ambiguous between a CC complement of told and an RC modifying the woman.

Theoretical Hypotheses

Two hypotheses frame the debate (@cite{paape-vasishth-2026}):

• Context-sensitive attachment: Discourse context modulates first-pass parsing choices. A mismatch between context and disambiguation (e.g., non-unique referents with CC continuation) increases garden-pathing. Predicts a context × disambiguation interaction.

• Context-insensitive attachment: The parser relies on purely syntactic preferences (e.g., minimal attachment), ignoring discourse context during first-pass processing. Context may only affect later reanalysis stages. Predicts a disambiguation main effect with no interaction.

@cite{paape-vasishth-2026} shows the answer is a graded compromise: first-pass parsing is partially context-sensitive, and context also affects reanalysis — "the answer is both."

Cross-references

• Related to FillerGap/: RC analysis involves a filler-gap dependency
• Related to Reference/: The context manipulation involves referential uniqueness (one vs. two potential referents for a definite NP)

inductive Phenomena.SyntacticAmbiguity.Disambiguation : Type

The two readings of a temporarily ambiguous CC/RC string.

• complementClause : Disambiguation

  Complement clause: told the woman [that he'd risked his life for many people]

• relativeClause : Disambiguation

  Relative clause: told [the woman that he'd risked his life for] to install ...

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instDecidableEqDisambiguation : DecidableEq Disambiguation

Equations

• Phenomena.SyntacticAmbiguity.instDecidableEqDisambiguation x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯

def Phenomena.SyntacticAmbiguity.instReprDisambiguation.repr : Disambiguation → Nat → Std.Format

Equations

• One or more equations did not get rendered due to their size.

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instReprDisambiguation : Repr Disambiguation

Equations

• Phenomena.SyntacticAmbiguity.instReprDisambiguation = { reprPrec := Phenomena.SyntacticAmbiguity.instReprDisambiguation.repr }

inductive Phenomena.SyntacticAmbiguity.ReferentialContext : Type

Referential context: whether the discourse makes the definite NP's referent uniquely identifiable without a modifier.

• uniqueReferent : ReferentialContext

  Only one possible referent (e.g., a man and a woman) — a bare definite the woman suffices, so an RC modifier is pragmatically unnecessary.

• nonUniqueReferents : ReferentialContext

  Multiple possible referents (e.g., two women) — a bare definite the woman violates uniqueness, so an RC modifier is pragmatically licensed.

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instDecidableEqReferentialContext : DecidableEq ReferentialContext

Equations

• Phenomena.SyntacticAmbiguity.instDecidableEqReferentialContext x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instReprReferentialContext : Repr ReferentialContext

Equations

• Phenomena.SyntacticAmbiguity.instReprReferentialContext = { reprPrec := Phenomena.SyntacticAmbiguity.instReprReferentialContext.repr }

def Phenomena.SyntacticAmbiguity.instReprReferentialContext.repr : ReferentialContext → Nat → Std.Format

Equations

• One or more equations did not get rendered due to their size.

def Phenomena.SyntacticAmbiguity.contextSupports : ReferentialContext → Disambiguation → Bool

Whether the referential context supports the disambiguation type. Non-unique referents support RC (the modifier is needed to identify the referent); unique referents support CC (no modifier needed).

Equations

• Phenomena.SyntacticAmbiguity.contextSupports Phenomena.SyntacticAmbiguity.ReferentialContext.nonUniqueReferents Phenomena.SyntacticAmbiguity.Disambiguation.relativeClause = true
• Phenomena.SyntacticAmbiguity.contextSupports Phenomena.SyntacticAmbiguity.ReferentialContext.uniqueReferent Phenomena.SyntacticAmbiguity.Disambiguation.complementClause = true
• Phenomena.SyntacticAmbiguity.contextSupports x✝¹ x✝ = false

structure Phenomena.SyntacticAmbiguity.Condition : Type

An experimental condition in the CC/RC × context design.

• disambiguation : Disambiguation
• context : ReferentialContext

def Phenomena.SyntacticAmbiguity.instDecidableEqCondition.decEq (x✝ x✝¹ : Condition) : Decidable (x✝ = x✝¹)

Equations

• One or more equations did not get rendered due to their size.

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instDecidableEqCondition : DecidableEq Condition

Equations

• Phenomena.SyntacticAmbiguity.instDecidableEqCondition = Phenomena.SyntacticAmbiguity.instDecidableEqCondition.decEq

def Phenomena.SyntacticAmbiguity.instReprCondition.repr : Condition → Nat → Std.Format

Equations

• One or more equations did not get rendered due to their size.

@[implicit_reducible]

instance Phenomena.SyntacticAmbiguity.instReprCondition : Repr Condition

Equations

• Phenomena.SyntacticAmbiguity.instReprCondition = { reprPrec := Phenomena.SyntacticAmbiguity.instReprCondition.repr }

def Phenomena.SyntacticAmbiguity.Condition.isMatch (c : Condition) : Bool

Whether disambiguation and context match (context supports the actual disambiguation).

Equations

• c.isMatch = Phenomena.SyntacticAmbiguity.contextSupports c.context c.disambiguation

def Phenomena.SyntacticAmbiguity.contextSensitivePrediction : Prop

The context-sensitive attachment hypothesis predicts that context and disambiguation interact: garden-path difficulty depends on whether the context supports the actual disambiguation.

Formalized as: for a fixed disambiguation type, changing context from supporting to non-supporting increases garden-path difficulty. For RC, this means non-unique → unique increases difficulty; for CC, unique → non-unique increases difficulty.

Equations

• One or more equations did not get rendered due to their size.

def Phenomena.SyntacticAmbiguity.contextInsensitivePrediction : Prop

The context-insensitive hypothesis predicts no interaction: the parser always prefers the syntactically simpler analysis (CC), and the same garden-path magnitude obtains regardless of context.

Equations

• Phenomena.SyntacticAmbiguity.contextInsensitivePrediction = True

def Phenomena.SyntacticAmbiguity.disambiguationProfile : Disambiguation → ProcessingModel.ProcessingProfile

RC disambiguation is harder than CC on the processing profile: the RC requires crossing a clause boundary (the relative clause) and involves a filler-gap dependency that increases locality.

Equations

• Phenomena.SyntacticAmbiguity.disambiguationProfile Phenomena.SyntacticAmbiguity.Disambiguation.relativeClause = { locality := 3, boundaries := 1, referentialLoad := 1, ease := 0 }
• Phenomena.SyntacticAmbiguity.disambiguationProfile Phenomena.SyntacticAmbiguity.Disambiguation.complementClause = { locality := 1, boundaries := 0, referentialLoad := 0, ease := 1 }

theorem Phenomena.SyntacticAmbiguity.rc_pareto_harder : (disambiguationProfile Disambiguation.relativeClause).compare (disambiguationProfile Disambiguation.complementClause) = ProcessingModel.CompareResult.harder

RC is Pareto-harder than CC.