According to the formalist’s motto (Haugeland, 1985) by taking care of the syntax, one also takes care of the semantics. The reason for this is that, like the rules in a logical system, the syntactic operations of a physical symbol system are constrained to preserve meaning. The symbolic expressions that a physical symbol system evolves will have interpretable designations.
We have seen that the structures a physical symbol system manipulates have two different lives, syntactic and semantic. Because of this, there is a corollary to the formalist’s motto, which might be called the semanticist’s motto: “If you understand the semantics, then you can take the syntax for granted.” That is, if you have a semantic interpretation of a physical symbol system’s symbolic expressions, then you can use this semantic interpretation to predict the future behaviour of the system—the future meanings that it will generate—without having to say anything about the underlying physical mechanisms that work to preserve the semantics.
We have seen that one of the fundamental properties of a physical symbol system is designation, which is a relation between the system and the world that provides interpretations to its symbolic expressions (Newell, 1980; Newell & Simon, 1976). More generally, it could be said that symbolic expressions are intentional—they are about some state of affairs in the world. This notion of intentionality is rooted in the philosophy of Franz Brentano (Brentano, 1995). Brentano used intentionality to distinguish the mental from the physical: “We found that the intentional in-existence, the reference to something as an object, is a distinguishing characteristic of all mental phenomena. No physical phenomenon exhibits anything similar” (p. 97).
To assume that human cognition is the product of a physical symbol system is to also assume that mental states are intentional in Brentano’s sense. In accord with the semanticist’s motto, the intentionality of mental states can be used to generate a theory of other people, a theory that can be used to predict the behaviour of another person. This is accomplished by adopting what is known as the intentional stance (Dennett, 1987).
The intentional stance uses the presumed contents of someone’s mental states to predict their behaviour. It begins by assuming that another person possesses intentional mental states such as beliefs, desires, or goals. As a result, the intentional stance involves describing other people with propositional attitudes.
A propositional attitude is a statement that relates a person to a proposition or statement of fact. For example, if I said to someone “Charles Ives’ music anticipated minimalism,” they could describe me with the propositional attitude “Dawson believes that Charles Ives’ music anticipated minimalism.” Propositional attitudes are of interest to philosophy because they raise a number of interesting logical problems. For example, the propositional attitude describing me could be true, but at the same time its propositional component could be false (for instance, if Ives’ music bore no relationship to minimalism at all!). Propositional attitudes are found everywhere in our language, suggesting that a key element of our understanding of others is the use of the intentional stance.
In addition to describing other people with propositional attitudes, the intentional stance requires that other people are assumed to be rational. To assume that a person is rational is to assume that there are meaningful relationships between the 84 Chapter 3 contents of mental states and behaviour. To actually use the contents of mental states to predict behaviour—assuming rationality—is to adopt the intentional stance.
For instance, given the propositional attitudes “Dawson believes that Charles Ives’ music anticipated minimalism” and “Dawson desires to only listen to early minimalist music,” and assuming that Dawson’s behaviour rationally follows from the contents of his intentional states, one might predict that “Dawson often listens to Ives’ compositions.” The assumption of rationality, “in combination with home truths about our needs, capacities and typical circumstances, generates both an intentional interpretation of us as believers and desirers and actual predictions of behavior in great profusion” (Dennett, 1987, p. 50).
Adopting the intentional stance is also known as employing commonsense psychology or folk psychology. The status of folk psychology, and of its relation to cognitive science, provides a source of continual controversy (Christensen & Turner, 1993; Churchland, 1988; Fletcher, 1995; Greenwood, 1991; Haselager, 1997; Ratcliffe, 2007; Stich, 1983). Is folk psychology truly predictive? If so, should the theories of cognitive science involve lawful operations on propositional attitudes? If not, should folk psychology be expunged from cognitive science? Positions on these issues range from eliminative materialism’s argument to erase folk-psychological terms from cognitive science (Churchland, 1988), to experimental philosophy’s position that folk concepts are valid and informative, and therefore should be empirically examined to supplant philosophical concepts that have been developed from a purely theoretical or analytic tradition (French & Wettstein, 2007; Knobe & Nichols, 2008).
In form, at least, the intentional stance or folk psychology has the appearance of a scientific theory. The intentional stance involves using a set of general, abstract laws (e.g., the principle of rationality) to predict future events. This brings it into contact with an important view of cognitive development known as the theory-theory (Gopnik & Meltzoff, 1997; Gopnik, Meltzoff, & Kuhl, 1999; Gopnik & Wellman, 1992; Wellman, 1990). According to the theory-theory, children come to understand the world by adopting and modifying theories about its regularities. That is, the child develops intuitive, representational theories in a fashion that is analogous to a scientist using observations to construct a scientific theory. One of the theories that a child develops is a theory of mind that begins to emerge when a child is three years old (Wellman, 1990).
The scientific structure of the intentional stance should be of no surprise, because this is another example of the logicism that serves as one of the foundations of classical cognitive science. If cognition really is the product of a physical symbol system, if intelligence really does emerge from the manipulation of intentional representations according to the rules of some mental logic, then the semanticist’s motto should hold. A principle of rationality, operating on propositional attitudes, should offer real predictive power.
However, the logicism underlying the intentional stance leads to a serious problem for classical cognitive science. This is because a wealth of experiments has shown that human reasoners deviate from principles of logic or rationality (Hastie, 2001; Tversky & Kahneman, 1974; Wason, 1966; Wason & Johnson-Laird, 1972). “A purely formal, or syntactic, approach to [reasoning] may suffer from severe limitations” (Wason & Johnson-Laird, 1972, p. 244). This offers a severe challenge to classical cognitive science’s adherence to logicism: if thinking is employing mental logic, then how is it possible for thinkers to be illogical?
It is not surprising that many attempts have been made to preserve logicism by providing principled accounts of deviations from rationalism. Some of these attempts have occurred at the computational level and have involved modifying the definition of rationality by adopting a different theory about the nature of mental logic. Such attempts include rational analysis (Chater & Oaksford, 1999) and probabilistic theories (Oaksford & Chater, 1998, 2001). Other, not unrelated approaches involve assuming that ideal mental logics are constrained by algorithmic and architectural-level realities, such as limited memory and real time constraints. The notion of bounded rationality is a prototypical example of this notion (Chase, Hertwig, & Gigerenzer, 1998; Evans, 2003; Hastie, 2001; Rubinstein, 1998; Simon, Egidi, & Marris, 1995).
The attempts to preserve logicism reflect the importance of the intentional stance, and the semanticist’s motto, to cognitive science. Classical cognitive science is committed to the importance of a cognitive vocabulary, a vocabulary that invokes the contents of mental states (Pylyshyn, 1984).