4.3 Thematic roles and case grammar

Thematic Roles and Case Grammar

Thematic roles describe how participants relate to predicates: who does what, to whom, where, and how. They let you analyze sentence meaning at a level deeper than syntax, capturing semantic relationships that stay constant even when grammatical structure shifts (like active vs. passive voice). This topic also covers case grammar, Charles Fillmore's framework that formalized these semantic relationships into a theory of sentence meaning.

Thematic Roles

Thematic Roles and Semantic Relationships

A thematic role is a semantic category that describes the relationship between a predicate (usually a verb) and its arguments (the noun phrases connected to it). Where grammatical roles like "subject" and "object" tell you about a word's position in a sentence, thematic roles tell you about its meaning in the event being described.

Consider the sentence "The window was broken by the child." Grammatically, the window is the subject. But semantically, it's the thing being acted upon (the patient), while the child is the one doing the acting (the agent). Thematic roles capture that semantic layer.

This matters because:

• Two sentences can have different syntax but assign the same thematic roles ("John kicked the ball" vs. "The ball was kicked by John" — John is the agent in both)
• Thematic roles give you a way to represent meaning independently of word order or voice

Assignment of Thematic Roles

Each thematic role labels a specific type of participant in an event or state. Here are the core roles you need to know:

• Agent: The participant that intentionally initiates or performs the action. In "John kicked the ball," John is the agent. Intentionality is the key feature — agents act on purpose.
• Patient: The participant that undergoes a change of state or is directly affected by the action. In "The vase was broken by the cat," the vase is the patient because its state changes (from intact to broken).
• Theme: The participant that is moved, located, or whose state is described. In "Mary gave the book to John," the book is the theme — it's the thing being transferred. Theme and patient overlap in some frameworks, but theme typically emphasizes movement or location rather than being affected.
• Experiencer: The participant that undergoes a mental or sensory state rather than performing a physical action. In "Sarah loves chocolate," Sarah is the experiencer. No physical action happens; she's in a psychological state.
• Instrument: The object or means used to carry out the action. In "He cut the rope with a knife," the knife is the instrument.
• Location: The place where the event or state occurs. In "The cat is sitting on the mat," the mat is the location.
• Recipient: The participant that receives something as a result of the action. In "John gave the book to Mary," Mary is the recipient.

Thematic vs. Grammatical Roles

This distinction trips people up, so it's worth being precise.

Grammatical roles (subject, direct object, indirect object) are defined by syntactic position and morphological marking. Thematic roles are defined by meaning — the semantic relationship between a participant and the predicate.

The crucial point is that these two systems don't map onto each other one-to-one:

• The same thematic role can appear in different grammatical positions. The agent John is the subject in "John kicked the ball" but appears in a prepositional phrase in "The ball was kicked by John."
• The same grammatical role can correspond to different thematic roles. John is the subject in both "John kicked the ball" (agent) and "John loves Mary" (experiencer), but his semantic relationship to the verb is completely different.

This is exactly why thematic roles are useful — they capture meaning that grammatical roles alone can't.

Case Grammar and Thematic Roles

Fillmore's Case Grammar

Case grammar is a theory proposed by Charles Fillmore in the late 1960s. Its central claim is that sentence meaning is determined by the semantic relationships between a predicate and its arguments, not by syntactic structure alone.

Fillmore argued that every predicate comes with a case frame — a specification of which semantic cases (his term for thematic roles) it requires. These cases were considered universal across languages, even though different languages express them through different syntactic means.

Fillmore's original semantic cases map closely onto modern thematic roles:

A case frame for a verb like "give" would specify that it requires an agentive (the giver), an objective (the thing given), and a dative (the receiver). This frame holds regardless of whether the sentence is active, passive, or restructured in any other way.

Case grammar was influential because it shifted attention from surface syntax to underlying semantic structure. It directly shaped later developments including theta theory (in generative grammar) and neo-Davidsonian event semantics, both of which build on the idea that predicates assign specific semantic roles to their arguments.