1. Intentionality and the Mental
An intuitive characterization of intentionality is as follows: (a) A state is intentional if it "points outside of itself", if it is characterized by "aboutness"; (b) An intentional state may be "about", it may "point to" something that doesn't exist; (c) An intentional state may be about something under one description, but not under another description.
Illustrations
(1) With regard to the second of these three features, suppose that the basketball coach wants a center who is over eight feet tall. The mental state of wanting a center who is over eight feet "points outside of itself", but what it is "about" - a center who is over eight feet tall -may not in fact exist.
(2) With regard to the third feature, suppose that the basketball coach would like to find the tallest person on campus. Suppose, further, that the tallest person on campus is identical with the coach's most severe critic, and the greatest serial killer of basketball coaches in history. It may very well not be the case that the basketball coach would like to find his most severe critic, and the greatest serial killer of basketball coaches in history.
2. Intensional Language and Intentional States
Points (b) and (c) in the preceding characterization of intentionality will be clearer, I think, if they are set out against the background of a distinction, within philosophy of language, between extensional and intensional contexts within sentences.
First, then, the concept of an extensional context. Consider the sentence:
"Sandra threw the ball to the boy across the street"Certain terms and expressions within that sentence refer to particular things - namely, the name, "Sandra", and the definite descriptions, "the ball". and "the boy across the street".
"Sandra threw the ball to the boy across the street"Each of the contexts occupied by those three expressions is extensional. What does that mean? The answer is that extensional contexts have two central features:
Feature 1: The Interchange of Co-Referential Terms Preserves Truth-Value
What does it mean to say that two terms are co-referential? The answer is that this is just to say that they refer to the very same object. So suppose that Sandra is Suzanne's older sister. Then the name "Sandra" and the description "Suzanne's older sister" refer to one and the same person. So those two expressions are co-referential. To say that the place occupied by the term "Sandra" in the above sentence is extensional is then to say that if the above sentence is true, then the sentence that results when the term "Sandra" is replaced by the expression "Suzanne's older sister" - namely, the sentence
"Suzanne's older sister threw the ball to the boy across the street"- must also be true. Similarly, if the original sentence was false, then the sentence that results from the interchange of the co-referential expressions must also be false.
The same applies to the other two contexts. So suppose that the ball in question was the thing that Mark found at the swimming pool, and that the boy across the street is the most radical dude in Boulder. Then the two expressions "the ball", and "the thing that Mark found at the swimming pool" are co-referential expressions - they refer to one and the same object, and, similarly, for the two expressions, "the boy across the street", and "the most radical dude in Boulder".
Consider, now the sentence that results when we transform the original sentence by interchanging all three pairs of co-referential terms:
"Suzanne's older sister threw the thing that Mark found at the swimming pool to the most radical dude in Boulder"If the original sentence is true, then this sentence must also be true, while if the original sentence is false, then so is this one. In short, whichever truth-value the original sentence has, the sentence that results from the interchange of co-referential expressions must also have the same truth-value.
Feature 2: Existential Generalization, or "Quantifying in," is Permissible
Consider, again, our original sentence:
"Sandra threw the ball to the boy across the street"If that sentence is true, then one can move from that sentence to related sentences, that will also be true, and that rather than naming or describing the people or things involved, simply assert that there are actual people or objects that stand in the relevant relations. Thus one can, for example, draw the following conclusion from the original sentence:
"There is some actual person who threw the ball to the boy across the street".Here the name "Sandra" has been eliminated, and one simply says that there is some actual person who performed the action in question. Similarly, one might eliminate the description "the ball", and merely assert that there is some actual object that was acted upon in the way described, as in the following sentence:
"There is some actual person, x, and there is some actual object, y, such that x threw y to the boy across the street"Finally, the same thing could be done for the expression "the boy across the street":
"There is some actual person, x, and there is some actual object, y, and there is another actual person, z, such that x threw y to z".To sum up, then: Extensional contexts are ones where (1) interchange of co-referential expressions cannot possibly alter the truth-value, and (2) existential generalization is necessarily a truth-preserving inference.
Intensional contexts, on the other hand, are contexts that lack these features. Consider, for example, the following sentence:
"Bruce believes that Apollo is an admirable god"Here the context occupied by the name "Apollo" is not an extensional context, as is shown by the fact that, even if the sentence in question is true, the sentence that results when one eliminates the name "Apollo" in favor of existential quantification - namely,
"There is an actual person such that Bruce believes that that person is an admirable god"- is not true. So the context occupied by the term "Apollo" is a context in which inference via existential generalization may very well not preserve truth.
For a context where interchange of co-referential terms may lead to a change in truth-value, consider the following sentence:
"Rip Van Winkle believes that the previous president of the United States is Ronald Reagan"The place occupied by the description, "the previous president of the United States", is not an extensional context. For although the expression "the previous president of the United States", and the name, "George Bush", refer to the very same individual, when one makes the relevant interchange in the above sentence, one gets a sentence - namely,
"Rip Van Winkle believes that George Bush is Ronald Reagan"- that may very well be false, even if the original sentence is true.
3. The Logical Structure Involved in the Two Features Discussed Above
Feature 1: Substitution of Co-Referential Terms Preserves Truth-Value
What is involved here is
a matter of the validity of the following inference:
Fa
a =b
Therefore: Fb
Feature 2: Existential Generalization, or "Quantifying
In", is Truth-Preserving
This is a matter of the validity of the following inference:
Fa
Therefore: (Ex)Fx
4. Intentional States and Intensional Contexts
As the sentences about
beliefs
illustrate, some sentences attributing mental states to a person
involve
intensional contexts. This is true not only in the case of
beliefs,
but also in the case of desires, thoughts, hopes, fears, etc., as the
following
sentences illustrate:
"Tom wants to find a way of squaring a circle"It is rather natural, then, to relate intentionality to the occurrence of intensional contexts within sentences that are used to attribute mental states to individuals. But while this is fine as far as it goes, a problem arises if one wants to use intentionality as a mark of the mental. For then it will not do to appeal to the occurrence of intensional contexts within sentences that are used to attribute mental states, since then one's account would be circular. Now if the only place where intensional contexts were to be found was in sentences used to attribute mental states, there would be no problem: one could define intentional states as those states that are attributed by means of sentences containing intensional contexts. But sentences that do not function to attribute mental states also contain intensional contexts:"John thinks that the third planet from the sun is Mars"
"Mary hopes that the lost continent of Atlantis will soon be found"
"Some Greeks feared Zeus more than any other gods"
"It is a logical truth that Bill Clinton is identical with Bill Clinton"For while Bill Clinton is identical with the present President of the United States, it does not follow that:"It is a necessary truth that 9 = 3 x 3".
"It is a logical truth that Bill Clinton is identical with the present President of the United States"Similarly, although it is true that the number 9 is identical with the number of the planets, it does not follow that:
"It is a necessary truth that the number of the planets = 3 x 3".Some philosophers - perhaps most notably Roderick Chisholm - have tried to show that one can distinguish between those sentences that have intensional contexts and that deal with mental states and those sentences that have intensional contexts but do not deal with mental states, and that one can do this without appealing to the concept of a mental state. If that is right, then one can make use of the notion of an intensional context to provide an explication of the concept of an intentional state that could, potentially, provide a non-circular mark of the mental. But that issue is rather complex, and I do not think that it worthwhile to pursue that issue here.