Predicate-Argument Structure

The predicate—typically a verb, but also a predicative adjective or noun—serves as the relational hub of the clause. It determines the number, type, and semantic roles of its arguments through its valency or arity.

• An intransitive verb like sleep has a valency of 1 (requires a sleeper).
• A ditransitive verb like give has a valency of 3 (requires a giver, a gift, and a recipient).
• The predicate's selectional preferences constrain the ontological category of each argument (e.g., the subject of sleep must be an animate entity).

A fundamental distinction exists between core arguments and peripheral adjuncts. Core arguments are essential participants required by the predicate's meaning to form a grammatically complete clause; adjuncts are optional modifiers adding circumstantial detail.

• In Mary put the book on the shelf, the locative on the shelf is a core argument of put.
• In Mary read the book on the shelf, the locative is an adjunct modifying the event.
• Diagnostic tests like obligatoriness and entailment distinguish the two categories.

Each argument is assigned a thematic role (theta-role) that captures its semantic relationship to the predicate. These generalized categories abstract over specific verbs to enable reasoning.

• Agent: The volitional initiator of an action (John broke the window).
• Patient: The entity undergoing a change of state (John broke the window).
• Theme: The entity that is moved, perceived, or located (John gave the book to Mary).
• Instrument: The means by which an action is performed (John broke the window with a hammer).
• Goal/Recipient: The endpoint or receiver (John gave the book to Mary).

The mapping between thematic roles and grammatical functions (subject, object) is not one-to-one. Diathesis alternations—such as the active/passive voice—rearrange this mapping while preserving core semantics.

• Active: [Agent The chef] cooked [Patient the meal].
• Passive: [Patient The meal] was cooked by [Agent the chef].
• The linking theory component of a grammar specifies the rules governing which thematic role surfaces in which syntactic position for a given predicate.

Arguments can be syntactically unrealized yet semantically present. Null arguments include pro-dropped subjects in languages like Spanish, and implicit objects in English.

• In John ate, the patient argument (the food) is implicit but semantically understood.
• Indefinite null complements (John ate something) differ from definite null complements (John noticed, where the stimulus is recoverable from context).
• Proper interpretation of null arguments is critical for accurate information extraction and question answering.

Two major resources formalize predicate-argument structures for computational use. PropBank annotates verb-specific numbered roles (Arg0, Arg1) mapped to prototypical thematic roles, while FrameNet defines semantic frames with frame-specific named elements.

• PropBank: expect has Arg0 (expecter), Arg1 (thing expected).
• FrameNet: The Commerce_buy frame evokes Buyer, Seller, Goods, and Money.
• These annotations provide the supervised training data for modern neural Semantic Role Labeling systems.

Generalized semantic categories that define the relationship between a noun phrase and the main verb. Unlike verb-specific roles, these are abstract archetypes.

• Agent: The deliberate initiator of an action (e.g., 'Mary' in 'Mary wrote the code').
• Patient: The entity undergoing the effect of an action (e.g., 'the code' in 'Mary wrote the code').
• Instrument: The tool or means used to perform an action.
• Experiencer: The entity that perceives or feels a sensory or emotional state.

The distinction between essential and optional participants in a clause.

• Core Arguments: Required by the verb's meaning to form a grammatically complete clause (e.g., subject and object for a transitive verb).
• Peripheral Arguments (Adjuncts): Optional modifiers providing circumstantial information like time, location, or manner.
• Null Arguments: Implicit participants that are syntactically unrealized but semantically understood, such as the dropped subject in pro-drop languages like Spanish.