4.2 Predicate-argument structure

Predicate-Argument Structure

Predicate-argument structure is a way of breaking down sentences into their core semantic components: the main verb (the predicate) and the entities involved (the arguments). This framework reveals the underlying relationships that give a sentence its meaning, regardless of the specific words or syntax used.

Understanding this structure is central to compositionality. Once you can identify the predicate and its arguments, you can see exactly how the parts of a sentence combine to produce meaning.

Predicate-Argument Structure Basics

A predicate is typically the main verb in a sentence. It describes an action or state. Arguments are the participants in that action or state.

• Together, the predicate and its arguments capture the core meaning of a sentence.
• This framework abstracts away from surface-level word choices and focuses on the semantic relationships underneath. For example, "The cat chased the mouse" and "The mouse was chased by the cat" have different syntax but the same predicate-argument structure: chase(cat, mouse).
• Predicate-argument structure is one of the most fundamental tools in semantic analysis because it gives you a consistent way to represent who did what to whom.

Identifying Predicates and Arguments

To find the predicate, locate the main verb that describes the action or state. To find the arguments, look for the noun phrases (NPs) that are semantically tied to that predicate.

Arguments come in two types:

• Obligatory arguments are required for the sentence to be complete. In "John gave a book to Mary," both "John" and "a book" are obligatory. Without them, the sentence doesn't hold together grammatically or semantically.
• Optional arguments (adjuncts) add information but aren't required. In that same sentence, "to Mary" provides the recipient, but "John gave a book" is still a grammatical sentence on its own.

The number and type of arguments a predicate requires is called its valency (or argument structure). "Sleep" has a valency of one (it needs only a sleeper), while "give" has a valency of three (a giver, a thing given, and a recipient).

Compositional Meaning Through Predicate-Argument Structure

Predicate-argument structure is where compositionality becomes concrete. The predicate defines the type of action or state, and the arguments specify who or what is involved. The meaning of the whole sentence is built from these pieces and how they fit together.

Semantic roles describe the function each argument plays:

• The agent is the entity performing the action.
• The patient (or theme) is the entity affected by the action.
• The recipient is the entity receiving something.

In "John broke the window," "John" is the agent and "the window" is the patient. Changing which argument fills which role changes the meaning entirely: "The window broke John" means something very different (if it means anything at all).

By analyzing predicate-argument structure, you can see exactly how meaning is constructed from individual components and their roles.

Applying Predicate-Argument Analysis

Predicate-argument structure can represent sentences of varying complexity using a simple notation where the predicate is written as a function and the arguments go inside parentheses.

Simple sentences with a single predicate are straightforward:

• "Alice sleeps" → $\text{sleep(Alice)}$
• "Bob kicked the ball" → $\text{kick(Bob, ball)}$

Complex sentences with multiple predicates use nested structures:

• "Alice believes that Bob loves Mary" → $\text{believe(Alice, love(Bob, Mary))}$

Here, $\text{love(Bob, Mary)}$ is itself an argument of $\text{believe}$. The embedded predicate-argument structure becomes a component of the larger one.

Sentences with adjuncts (optional modifiers) can also be represented, though adjuncts are typically distinguished from core arguments:

• "Alice runs quickly" → $\text{run(Alice)}$ with "quickly" as a modifier on the event, not a core argument

Some notations represent this as $\text{quickly(run(Alice))}$, treating the adverb as a higher-order predicate that modifies the running event. Your course may prefer one notation over the other, so check which convention is expected.

The key takeaway: predicate-argument structure gives you a systematic way to represent the core meaning of any sentence, no matter how complex, by identifying the predicate and slotting each participant into its proper role.