Minds and Machines Summer 2011 Tuesday, 07/26

Propositional Attitudes 1. What exactly are the mental states that relate us to propositions? What is a thought, a belief, a hope, a desire? 2. How does a mental state, of whatever stripe, manages to relate a person to a proposition? What is it to “grasp” a proposition? 3. What explains the difference between the various ways of entertaining propositions (e.g. believing, hoping, desiring)? 4. Why is it that entertaining some propositions, in certain ways, leads us to systematically (rationally, intelligibly) entertain certain others, in certain appropriate ways? What’s the scientific explanation of this fact?

Propositional Attitudes

Common Sense Psychology Demetrius: O, why rebuke you him that loves you so? Lay breath so bitter on your bitter foe. Hermia: Now I but chide; but I should use thee worse, For thou, I fear, hast given me cause to curse, If thou hast slain Lysander in his sleep, Being o'er shoes in blood, plunge in the deep, And kill me too. The sun was not so true unto the day As he to me: would he have stolen away From sleeping Hermia? I'll believe as soon This whole earth may be bored and that the moon May through the centre creep and so displease Her brother's noontide with Antipodes. It cannot be but thou hast murder'd him; So should a murderer look, so dead, so grim.

Common Sense Psychology Fodor’s Analysis: Hermia has reason to believe herself beloved of Lysander. But if Lysander loves Hermia, then Lysander wishes Hermia well. And if Lysander wishes Hermia well, then Lysander doesn’t voluntarily desert Hermia at night in a dark forest. But Hermia was, in fact, so deserted by Lysander. Therefore Lysander left involuntarily. So it’s is plausible that Lysander has come to harm.

Common Sense Psychology At whose hands? Plausibly at Demetrius’s. For Demetrius is Lysander’s rival for the love of Hermia. Hermia believes that Demetrius believes that a live Lysander is an impediment to the success of his (Demetrius’s) wooing of her (Hermia).

Common Sense Psychology Moreover, Hermia believes that if x wants that P, and x believes that not-P unless Q, and x believes that x can bring it about that Q, then x (typically) tries to bring it about that Q. Additionally, Hermia believes that, typically, people succeed in bringing about what they try to bring about. Believing all this, Hermia infers that perhaps Demetrius has killed Lysander.

Common Sense Psychology In fact, it turns out that Hermia is wrong. The theory Hermia implictly relies on to make sense of what Lysander did and what Demetrius may have done does not take into account nonturnal interventions by mischievous fairies. Granting, however, that the theory fails from time to time, it is largely successful in explaining and making predictions about people’s behavior.

Common Sense Psychology Works so well it disappears. In California, my brother tells me that he’ll meet me in New York in three weeks at a certain time. Three weeks later at that time I’m waiting for him at the airport. Common sense psychology tells me how to infer people’s intentions from the sounds they make and how to infer people’s behavior from their intentions. Imagine if we could do so well with predicting the weather! And think about how much more complicated the causes of behavior must be compared to the causes of the weather!

Common Sense Psychology “If you want to know where my physical body will be next Thursday, mechanics—our best science of middle-sized objects after all, and reputed to be pretty good in its field—is no use to you at all. Far the best way to find out (usually, in practice, the only way to find out) is: ask me! (Fodor)

Common Sense Psychology Not just a collection of truisms or platitudes, but a sophisticated theory, in many respects similar to the theories we have in science. Includes generalizations that refer to unobservable items. Does not appear to be a Behaviorist theory: its generalizations don’t directly link each mental state with behavior but specify how different states causally interact, e.g. with preferences and beliefs, so as to lead to actions. E.g. Hermia doesn’t have a simple generalization that tells her that if x is y’s rival, then x kills y. Rather, the generalization she uses may look more like this “if x is y’s rival, then x prefers y to suffer, all else being equal”. This, in turn, links to behavior/action in complex ways.

Common Sense Psychology Fodor claims that it is (1) a Mentalist theory (since it makes reference to mental states) and (2) a Realist theory (since it assumes that the mental states causally affect one another and the world). Fodor argues that common-sense psychology is practically indispensible. “We have no idea of how to explain ourselves to ourselves except in a vocabulary which is saturated with [common sense] psychology…We can’t give [it] up because we don’t know how to.

Common Sense Psychology Fodor’s goal is to find a scientifically respectable way to hold on to common sense psychology or to “vindicate” our talk about beliefs, desires, and so on. “Holding onto the attitudes—vindicating commonsense psychology—means showing how you could have…a respectable science [that] explicitly acknowledges states that exhibit the sorts of properties that common sense attributes to the attitudes.”

The essence of propositional attitudes They are semantically evaluable. They have causal powers. The implicit generalizations of commonsense belief/desire psychology are largely true of them. A scientific psychology provides means to “vindicate” or hold on to the attitudes just in case it postulates states (entities, events, etc.) satisfying 1-3.

Representational Theory of Mind (RTM) A framework for understanding the propositional attitudes, defined by these claims: 1. Propositional attitudes pick out computational relations to internal representations. E.g. to believe such-and-such is to have a token mental symbol that means that such and such and that meets a certain “job-description”. Mental processes are causal processes that involve transitions between internal representations. E.g. a train of thoughts is a causal sequence of tokenings of mental representations. According to Fodor, RTM provides way to hold on to our common sense psychology.

Language of Thought Hypothesis (LOTH) Empirical thesis about the nature of thought and thinking, not an analysis of our concepts. A way to answer the question: How is thinking/rationality mechanically possible? An elaboration of RTM. Postulates that thought and thinking take place in a mental language. This language consists of a system of representations that is physically realized in the brain of thinkers and has a combinatorial syntax (and semantics) such that operations on representations are causally sensitive only to the syntactic properties of representations.

Language of Thought Hypothesis (LOTH) So-called since the token mental representations are like sentences in a language in that they have a syntactically and semantically regimented constituent structure. The mental representations that are the direct “objects” of attitudes are structurally complex symbols whose complexity lends itself to a syntactic and semantic analysis. Useful to think of it not as a detailed proposal but as a foundational thesis, e.g. the “Atomic Hypothesis”.