Dretske's Compass

Intentionality vs. Intensionality

To understand Dretske's argument, we must first distinguish intentionality-with-a-t from the linguistic notion of intentionsionality-with-an-s. “Intensionality” is a term-of-art in the Philosophy of Language. Fortunately, intensionality is not nearly as difficult to understand as intentionality, although one grants the 's' for 't' business is cheeky.

Let us say that two terms are co-refer iff each term refers to the same object. For example,

“Spiderman” refers to Aunt May's web-slinging superhero nephew.

”Peter Parker” refers to Aunt May's web-slinging superhero nephew.

Thus “Spiderman” and “Peter Parker” are co-referring expressions.

Let us further say that two predicates are co-extensional iff their extension is the same class of objects. Borrowing Quine's example,

The extension of the predicate “renate” is the class of all creatures with a kidney.

The extension of the predicate “chordate” is the class of all creatures with a heart.

Since every renate is a chordate, and vice versa, it follows that “renate” and “chordate” are co-extensional predicates.

Finally, we say that a term or predicate occurs in an extensional context in a statement iff the term or predicate can be replaced by a co-referring term or a co-extensional predicate without changing the truth-value of the statement (salve veritate is the Latin phrase.) A term or predicate occurs in an intensional or opaque context in a statement iff the term or predicate cannot be replaced by a co-referring term or a co-extensional predicate salve veritate. For example, the terms “Peter Parker” and “Spiderman” occur in extensional contexts in the statements,

Peter Parker is a college student.

Spiderman sacrificed Mary Jane.

since the terms can be replaced one for the other salve veritate: “Spiderman is a college student” is still true and “Peter Parker sacrificed Mary Jane” is still false.

Similarly for the co-extensional predicates “renate” and “chordate” in the statements,

The baboon is a renate.

The starfish is a chordate.

Contrast these examples with the following,

  1. Jay believes that Peter Parker is a college student.
  2. Kay believes that the baboon is renate.

Can we replace “Peter Parker” in (1) with “Spiderman”? No, of course not. Jay may believe that Peter Parker is a college student and vigorously deny that Spiderman is a college student. Similarly, Kay may not know that all renates are chordates, so we cannot replace “renate” in (2) with “chordate” salve veritate.

In short, everything after “believes that” in the ascription of belief occurs in an intensional context. The ascription, that is, of intentional states generates intensional contexts, and it is this fact Dretske will use to argue that even the lowly compass exhibits original intentionality.

Dretske's Argument

Consider the following statement:

The compass indicates the magnetic north.

Now, it just so happens that the magnetic north is the arctic pole, and the arctic pole is the habitat of polar bears. That is, the terms

”the magnetic north”

”the arctic pole”

and

”the habitat of polar bears”

happen to co-refer, but need not and sometimes have not co-referred. That is, we cannot replace “the magnetic north” in

The compass indicates the magnetic north.

with either “the arctic pole” or “the habitat of polar bears” salve veritate, since it is only a coincidentally true that

The compass indicates the arctic pole.

given the co-incidence of magnetic north and the arctic pole, and it is simply false that

The compass indicates the habitat of polar bears.

as any trip to the zoo will demonstrate.

Dretske's Compass
 
  1 If ascribing a property to X generates an intensional context, then X exhibits original intentionality.  
  2 Ascribing the property of indicating the magnetic north to a compass generates an intensional context.  
3 A compass exhibits original intentionality. 1&2
 

There are, of course, a number of questions to be asked about this argument. In particular, one wants to know whether any counter-examples can be found to (1). That is, are there any objects X such that the ascription of a property to X generates an intensional context yet X clearly does not exhibit original intentionality?