Propositional Attitude Verbs
Propositional attitude verbs express mental states directed at propositions. Words like "believe," "want," and "know" all take a that-clause (a sentential complement) and tell you something about how a person relates to the content of that clause. These verbs sit right at the intersection of semantics and pragmatics because they connect the literal content of sentences to the mental lives of speakers and hearers.
They also create real headaches for formal semantics. Inside a propositional attitude context, you can't just check whether something is true in the actual world. Truth depends on what's going on in someone's head. That shift from extensional to intensional reasoning is what makes this topic both important and tricky.
What Are Propositional Attitude Verbs?
A propositional attitude verb expresses a subject's mental state or attitude toward a proposition. The verb takes a sentential complement, a clause that expresses a full proposition, as its argument.
"John believes [that the Earth is round]."
Here, believes is the propositional attitude verb, and that the Earth is round is the sentential complement expressing the proposition.
Common examples include believe, think, know, want, hope, fear, desire, and intend. You can use them to report someone else's mental state ("Sarah thinks the party starts at 8 pm") or to express your own ("I hope you'll join us for dinner").
Semantic Properties of Attitude Verbs
Not all attitude verbs work the same way. They differ along several dimensions.
By type of attitude:
- Belief verbs (believe, think, know) express the subject's commitment to the truth of the complement. "John believes that the Earth is round" tells you John takes that proposition to be true.
- Desire verbs (want, hope, wish) express the subject's preference for the proposition to be true. "Sarah wants to win the race" indicates Sarah has a desire for the state of affairs where she wins.
- Intention verbs (intend, plan) express the subject's commitment to bringing the proposition about through action. "I intend to finish the project by Friday" conveys a commitment to acting in a way that makes that proposition true.
By factivity:
One of the most important distinctions is factivity, whether the verb presupposes the truth of its complement.
- Factive verbs (know, realize, regret) presuppose that the complement is true. If you say "John knows that the Earth is round," you're taking it as given that the Earth is round. If it turned out not to be true, the sentence wouldn't just be false; it would be infelicitous.
- Non-factive verbs (believe, think, suspect) carry no such presupposition. "John believes that the Earth is flat" is a perfectly fine sentence even though the complement is false. It just reports what's in John's head.
This factivity distinction matters because know and believe can embed the same proposition but carry very different commitments about whether that proposition is actually true.
The Role of Propositional Attitudes in Semantics and Pragmatics
Connecting Language and Mind
Propositional attitude verbs are the primary tool language gives us for talking about mental states. They let speakers express beliefs, desires, and intentions, and they let hearers figure out what's going on in a speaker's mind based on what they say.
This matters for the semantics-pragmatics boundary. Consider: "John believes that the Earth is flat." The literal meaning reports John's belief. But pragmatically, the speaker is distancing themselves from that belief. They're not endorsing it as true. The attitude verb is doing crucial work in signaling whose commitment is whose.
Attitude verbs also reveal fine-grained meaning distinctions that go beyond truth conditions. "John believes that the Earth is round" and "John knows that the Earth is round" could both be true in the same situation, but they communicate different things about John's epistemic state and about the speaker's own commitments (since know is factive and believe is not).
More broadly, the existence of these verbs suggests something about how humans think: we represent the world in terms of propositions and hold various attitudes toward them. Language gives us a way to express and reason about those representations.
Challenges in Formal Semantics
Propositional attitudes create several well-known problems for formal semantic theory.
Intensionality and substitution failure. In ordinary (extensional) contexts, you can swap co-referential terms without changing truth value. But attitude contexts break this. Consider:
"John believes that Mark Twain wrote Huckleberry Finn" can be true while "John believes that Samuel Clemens wrote Huckleberry Finn" is false, even though Mark Twain is Samuel Clemens.
The problem is that John might not know the two names refer to the same person. This is a classic failure of substitutivity, and it shows that meaning inside attitude contexts is more fine-grained than mere reference.
De re vs. de dicto ambiguity. Sentences with attitude verbs can be interpreted in two ways:
- De re ("about the thing"): The attitude is about a specific individual in the world, regardless of how they're described. "John believes that the mayor is corrupt" on a de re reading means there's a particular person (who happens to be the mayor) that John believes is corrupt.
- De dicto ("about what is said"): The attitude is about the description itself. On a de dicto reading, John believes the proposition the mayor is corrupt, and he might not even know who the mayor is.
Capturing this ambiguity requires semantic tools that can represent the difference between attitudes directed at individuals and attitudes directed at descriptions.
Logical omniscience. Standard modal logic models for belief treat agents as believing all the logical consequences of their beliefs. If John believes P, and P logically entails Q, then the model says John believes Q too. This is psychologically unrealistic. People have limited reasoning abilities and can hold inconsistent beliefs without realizing it.
Proposed solutions. Researchers have developed several frameworks to handle these challenges:
- Possible worlds semantics: Models attitudes using accessibility relations between possible worlds. To believe P is for P to be true in all worlds compatible with your beliefs.
- Structured propositions: Represents the internal structure of propositions (not just their truth conditions) to account for why "Mark Twain wrote Huckleberry Finn" and "Samuel Clemens wrote Huckleberry Finn" can differ in attitude contexts.
- Two-dimensional semantics: Distinguishes between the context of utterance and the context of evaluation, providing extra structure to handle intensional contexts.
- Hyperintensional semantics: Introduces even finer-grained meaning distinctions using tools like impossible worlds or structured meanings, going beyond what possible worlds alone can capture.
Each approach has trade-offs. Possible worlds semantics is elegant but runs into the logical omniscience problem. Structured propositions handle substitution failures well but add complexity. For an intro course, the key takeaway is that standard extensional semantics isn't enough, and the field has developed increasingly sophisticated tools to deal with the intensional contexts that attitude verbs create.