The propositional character of belief
It can appear mysterious that the content of epistemic attitudes (belief and opinion) is conveyed by clauses introduced by that: “I believe that the dog is in his house.” If beliefs were causes of behavior, our success in denoting them gives rise to an apparently insurmountable problem: how do propositions—if they exist at all—exist independently of human conduct, so as to be fit for causally explaining it?
While belief ascriptions figure prominently in many behavioral explanations, their propositional form indicates that they pertain to states of information. My belief that my dog is in his house consists of the reliable use of the information that he’s there. Not only will I reply accordingly if asked about his location; in directing other my conduct, I may use that information. If I want the dog to come, I will yell in the direction of his house rather than toward his sofa. Yet, I won’t always use this information: I might absent-mindedly call to my dog on the sofa despite knowing (hence believing) that he is in his house. Believed information can be mistakenly disregarded.
Belief “that p” is a propensity to take p into rational account when p is relevant to the agent’s goals. But taking certain information into account involves also various skills, and it must be facilitated by the appropriate habits. The purposeful availability of believed information is also affected by, besides skills, inhibitions, habits, and desires.
What becomes striking on recognizing beliefs as propensities to use particular information is that behavior can be so successfully explained, when we know something of an agent’s purposes, by reference to the information on which we can predict the agent’s reliance.
Is this successful reliance a unique feature of human cognition? We can use belief ascriptions to describe nonhuman behavior, but we can do the same for machines. The concept of belief, however, isn’t essential to describing nonintelligent machine behavior. When my printer’s light indicates that it is out of paper, I might say it believes it is, particularly if, in fact, the tray is full. The printer’s “belief” that it is out of paper is expressed in two ways: it refuses to print and a light turns on, and I can refer to these directly, without invoking the concept of belief. Compare it to what is true of me when I run out of paper, where my belief that I have exhausted my supply can explain an indefinitely large set of potential behaviors, from purchasing supplies to postponing work to expressing frustrated rage—in any of an indefinitely large variety of manners.
Applying the concept of belief to nonhuman animals is intermediate between applying it to machines or to humans; it can be applied to animals more robustly than to machines. It isn’t preposterous to say that a dog believes his bone is buried at a certain location, particularly if it’s been removed and he still tries to retrieve it from the old location. What can give us pause about saying the dog believes arises from the severely limited conduct that’s influenced by the dog’s information about the bone’s location, as is apparent when the dog fails, except when hungry, to behave territorially toward the bone’s burial place.
Humans differ from canines in our capacity to carry the information constituting a belief’s propositional content to indefinitely many contexts. This makes belief indispensable in forecasting human behavior: without it, we could not exploit the predictive power of knowing what information a human agent is likely to rely on in new contexts.
This cross-contextual consistency in use of information seems to rest on our having language, which permits (but does not compel!) the insertion of old information into new contexts.
The social representation of abstractions
Explaining our cross-contextual capacities is the problem (in the theory of knowledge) of how we manage to mentally represent abstractions. In Kripke’s version of Wittgenstein’s private-language argument, the problem is expressed in the dependence of concepts on extensions that are not rule-governed. The social consensus engendered by how others apply words provides a standard against which to measure one’s own word usage.
Abstraction relies, ultimately, on the “wisdom of crowds” in achieving the most instrumentally effective segmentations. The source of abstraction—a form of social coordination—lies in our capacity to intuit (but only approximately) how others apply words.
The capacity to grasp the meanings of others’ words underlies the fruitfulness of using believed propositions to forecast human behavior. With language we can represent the information that another human agent is also able to represent and can transfer to all manner of contexts. But this linguistic requirement for full-fledged belief does not mean that people’s beliefs are always the beliefs they claim (or believe) they have. Language allows us our propositional knowledge about abstract informational states, but that doesn’t imply that we have infallible access to those states—obviously not pertaining to others but not even about ourselves. Nor does it follow that nonlinguistic animals can have full-fledged beliefs limited only by concreteness. Nonlinguistic animals lack full-fledged beliefs about even concrete matters because linguistic representation is the only available means for representing information in a way allowing its introduction to indefinitely varied contexts.
This account relies on a weakened private-language argument to explain abstraction as social consensus. But I reject Wittgenstein’s argument that private language is impossible: we do have propositional states accessible only privately. Wittgenstein’s argument proves too much, as it would impugn also the possibility of linguistic meaning, for which there is no fact of the matter as to how society must extend the meaning to new information. The answer to the strong private-language argument is the propositional structure of perception itself. (See T. Burge, Origins of Objectivity (2010).) What language provides is a consensual standard against which one’s (ultimately idiosyncratic) personal standard can be compared and modified. (Notice that this invokes a dialectic between what I’ve termed “opinion” and “belief.”)
This account language's role in abstraction justifies the early 20th-century Russian psychologist Vygotsky’s view that abstract thought is fundamentally linguistic.