Propositional attitudes are mental states with representational content. Belief is the most prominent example of a propositional attitude. Others include intention, wishing and wanting, hope and fear, seeming and appearing, and tacit presupposition. Verbs of propositional attitude express a relation between an agent and some kind of abstract object -- the content of the attitude, the object that is denoted by a nominalized sentence. So a statement such as "Fred believes that fleas have wings" says that Fred stands in the believes relation to that fleas have wings. The predicate "believes that fleas have wings" expresses a property that is ascribed to Fred. A philosophical account of propositional attitudes must answer two interrelated kinds of questions: first, what kind of thing is the content of an attitude (what is the object denoted by the that-clause)? Second, how can the states of mind of agents relate them to such objects? The problem of explaining how mental states can have representational content is the problem of INTENTIONALITY.
A propositional attitude -- more generally, any state or act that can be said to be representational -- represents the world as being a certain way, and the content of the attitude is what determines the way the world is represented (see MENTAL REPRESENTATION). So propositions must be objects that have truth conditions that must be satisfied for a representational state with that content to correctly represent the world.
Many different accounts of the contents of propositional attitudes have been proposed. Often, propositions are assumed to be complex objects, ordered sequences with ordered sequences as parts that reflect the recursive semantic structure of the sentences that express the proposition. In one kind of account of structured propositions, the primitive constituents are taken to be Fregean senses, modes of presentation (see SENSE AND REFERENCE), or CONCEPTS. In an alternative account of structured propositions, the constituents are individuals, properties, and relations. So, for example, the proposition that Booth killed Lincoln might contain, as constituents, the senses of the names "Booth" and "Lincoln" and of the verb "kill," or alternatively, the men Booth and Lincoln and the killing relation.
Both of these kinds of account treat the content of propositional attitudes as a recipe for determining the truth conditions of the representation. A third alternative is to take propositional contents -- the referents of that-clauses -- to be the truth conditions themselves. In this account, the proposition that Booth killed Lincoln can be identified with the set of possible circumstances in which Booth killed Lincoln. This conception of a proposition -- call it an informational content -- is the most coarse-grained conception of representational content. Any structured proposition will determine a unique informational content, but different structured propositions may have the same informational content.
The choice between different accounts of content depends on the role of content in determining the propositional attitudes -- the way in which the properties such as believing that Booth killed Lincoln are determined as a function of the content that Booth killed Lincoln. The more fine-grained conceptions of content will be justifiable only if the distinctions between different fine-grained contents with the same informational content play a role in distinguishing different states. We also need a conception of content that can account for intuitive judgments about attitudes. If it is intuitively obvious that believing that P is different from believing that Q, then we need a notion of content according to which "that P" and "that Q" denote different propositions. The defender of the coarse-grained conception of content needs to reconcile this account with apparently conflicting intuitions (see LOGICAL OMNISCIENCE).
The problem of propositional attitudes is often discussed in the context of a problem of semantics: the problem of giving the compositional semantics for propositional attitude reports. The focus of attention in such discussions has been on the role of pronouns and other context dependent expressions, and of quantification in belief contexts. The problems are closely connected: obviously, the question, "what kind of object is the content of a belief?" cannot be answered independently of the question, "what kind of object is the referent of a that-clause?" But the question about the semantics of attitude reports needs to be distinguished from the philosophical problem of explaining what propositional attitude properties are, and what it is that gives them their content. There are a number of alternative strategies that have been developed for giving such explanations.
First, in one familiar kind of account of propositional attitudes, belief and desire are correlative dispositions that are displayed in rational action (see RATIONAL AGENCY and INTENTIONAL STANCE). Roughly, to believe that P is to be disposed to act in ways that would satisfy one's desires if P (along with one's other beliefs) were true, and to desire that P is to be disposed to act in ways that would tend to bring it about in situations in which one's beliefs were true. This is only a very rough sketch of a strategy of locating belief and desire in a general theory of action. Because belief and desire are explained in terms of each other, the strategy does not offer the promise of a reductive analysis of propositional attitudes, and must be supplemented with additional constraints if the contents of attitudes are not to be wholly indeterminate.
A second strategy that may supplement the first -- the information theoretic strategy -- is to explain representational states in terms of causal and counterfactual dependencies between the agent and the world (see INFORMATIONAL SEMANTICS). One may explain the content of the representational states of an agent in terms of the way those states tend to vary systematically in response to states of the environment. A state of a person or thing carries the information thatP if the person or thing is in the state because of the fact that P, and would not be in the state if it were not the case that P. The strategy is to explain the content of representational states in terms of the information that the states tend to carry, or the information that the states would carry if they were functioning properly, or if conditions were normal. The information theoretic strategy will give determinate content to representational states only relative to some specification of the relevant normal conditions. A central task of the development and defense of the information-theoretic strategy is to give an account of these conditions.
A third strategy -- the linguistic strategy -- is to begin with linguistic representation, and to explain the content of mental states in terms of the content of sentences that realize the mental states, or of sentences to which the agent is disposed to assent. One version of this strategy, defended by Jerry Fodor (1987) among others, assumes that propositional attitudes are realized by the storage (in the "belief box," to use the popular metaphor) of sentences of a LANGUAGE OF THOUGHT. Another version takes a social practice of speech as primary, accounting for the contents of beliefs in terms of the contents of the sentences of the public language that the agent "holds true," or to which the agent is disposed to assent. Donald Davidson (1984) has defended this kind of strategy (see RADICAL INTERPRETATION). The first version of the linguistic strategy needs a distinction between explicit or "core" beliefs and implicit beliefs, because it would not be plausible to say that everything believed is explicitly stored. The second version has a problem explaining attitudes with content that is not easily expressed in linguistic form (for example, perceptual states), and it seems to conflict with the intuition that thought without the capacity for speech is at least a possibility. Both accounts need to be supplemented with some account of what it is in virtue of which the relevant kind of linguistic representations have content.
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