In a recent post I told the story of Ralph, 'Hesperus' and 'Phosphorus'. We saw there why Ralph might assert
('h≠p') 'Hesperus ≠ Phosphorus'
and how astronomical observation might lead him to change his mind. Remarkably, at no point in telling that story did we find any reason to deny that
(Bh=p) Ralph believes Hesperus = Phosphorus.
It was not that we refused to take Ralph at his word. Ex hypothesi, Ralph is a competent speaker of English and we took him to be sincere when he asserted ('h≠p'). We had to conclude that:
(Bh≠p) Ralph believes Hesperus ≠ Phosphorus.
The principle at work here is an important one. I call it (following Kripke) "The Disquotation Principle":
(DP) If someone understands a sentence and believes that it is true then they will believe what the sentence says.
If we restrict ourselves to unambiguous, non-indexical English sentences we can express this more formally as.
(DP) If x believes┌p┐ is true & x understands ┌p┐ .⊃ x believes p.
I think (DP) is true, indeed I'm happy to call it a necessary or, if you prefer, an analytic truth about belief and understanding. (DP) is what makes language useful: learning what sentences others think are true or false tells us what they believe and disbelieve. So when Ralph asserts ('h≠p') I conclude that Bh≠p.
But Bh≠p doen't entail that Bh=p is false. Of course Ralph doesn't think the sentence,
(h=p) 'Hesperus = Phosphorus'
is true. But Ralph does think that the sentence
('h=h') 'Hesperus = Hesperus'
is true. Which means, given (DP) that we must say that:
(Bh=h) Ralph believes that Hesperus = Hesperus.
And if we say (Bh=h) is true then Leibniz’s Law requires that we say that (Bh=p) is true. After all Hesperus is Phosphorus, and by the principle of the Indiscernibility of Identicals , anything true of Hesperus must be true of Phosphorus. It follows that if Hesperus has the property of being-believed-by-Ralph-to-be-Hesperus then so must Phosphorus.
Thus we found ourselves saying that Ralph believes inconsistent and necessarily false propositions. But that did not trouble us because we saw that it was a mistake to judge the reasonableness of Ralph's inferences or states of mind by looking at the propositions he believes. We understood what sort of situation Ralph thinks he is in and why and how this might lead him to say the things that he does.
All this should seem remarkable because it means that we managed to make sense of Ralph without ever having to invoke what philosophers call the "narrow" or "referentially opaque" or "notional style" of belief talk. We never had any reason to say that Ralph believes anything about Hesperus that he doesn't believe about Phosphorus. And a good thing too since that would have put us in a jam: it would have put our psychology on a collision course with Leibniz’s Law.
That is precisely the jam that Frege finds himself in at the beginning of On Sense and Reference.
People forget that OS&R begins with a psychological question: how to explain the difference in "cognitive value" between identity sentences like 'h=h' and 'h=p'. How, Frege asks, can Ralph simultaneously think (h=p) is false and (h=h) true? Frege takes the obvious answer -- the obvious psychological explanation for these different attitudes -- to be that (Bh=p) is false even while (Bh=h) is true. The balance of the essay (and, one might add, a good deal of twentieth century philosophy) is an attempt to explain how that can be so.
But is it so? Is Frege's psychology sound? Frege takes it for granted that if Ralph denies 'h=p' it must be because he doesn't believe that Hesperus = Phosphorus. This assumes what we will call (again, following Kripke), "The Quotation Principle".
(QP) If x understands a sentence and believes what it says, then x will believe the sentence is true.
(QP) If x understands ┌p┐ & x believes p .⊃ x believes ┌p┐ is true.
It is only this assumption that forces us to count Ralph's denial of 'h=p' as proof that Bh=p is false.
I think (QP) is wrong. I don't mean that I think there are puzzle cases or tricky counter-examples. I mean wrong. I don't think people ever believe that sentences are true because they believe the propositions those sentences express. I offer this as an empirical claim, because I take (QP) to be contingently false and I take cases like Ralph's as evidence that this is so. But the argument won't be that simple because, as we shall see, Frege assumes (QP) to be analytically true, and this assumption regiments everything he and his successors have understood about meaning and belief.
So my purpose just now is not to convince you that (QP) is wrong but to show you how much hangs upon it.
We've just observed that (QP) is essential to Frege's way of arguing for the referential opacity of belief. Now notice that there is no other way to argue for the opacity of belief except Frege's way. The referential opacity of the attitudes is usually cited as the hallmark of the "intentionality" of the propositional attitudes. It is supposed to separate the intentional from the merely intensional. But if we reject (QP) we would have no reason treat the propositional attitudes as referentially different from any intensional construction.
I'm sure that there are philosophers who will want to tell me that failures of substitutivity in the attitudes are somehow “intuitively” obvious. That they are part of "folk psychology". They might point out that it would sound odd or inappropriate to most folks to say that Ralph believes Hesperus is Phosphorus when Ralph is all the while insisting 'Hesperus isn't Phosphorus'. But intuitions about what it might seem odd or appropriate to say are beside the point. For substitutivity to fail we need evidence that bh=p is literally false even when bh=h is true. And this needs evidence. The propositional attitudes are theoretical entities. We postulate them to explain behavior. And however folksy our psychology may be, Ockham's razor applies: If you are going to claim that there is a difference between one belief and another you must be prepared to say what difference having one rather than the other might make in someone’s behavior.
But what difference could having a Hesperus belief rather than a Phosphorus belief make to Ralph's behavior? He doesn't behave differently towards Hesperus than he does towards Phosphorus. He can't; Hesperus is Phosphorus. He can't look at, point to, throw rocks at, travel to, flee from or fart in the general direction of Hesperus without doing likewise to Phosphorus and vice versa.
No one can behave differently toward towards Hesperus than Phosphorus they can only behave differently to the words 'Hesperus' and 'Phosphorus'. The only evidence for the referential opacity of the attitudes -- the only evidence there can be -- is linguistic behavior; and it is only evidence under the assumption of (QP).