No evidence for singular thought
Teaching for this semester is finally over.
Last week I gave a talk in Umea at a workshop on singular thought. I was pleased to be invited because I don't really understand singular thought. Giving a talk, I hoped, would force me to have a closer look at the literature. But then I was too busy teaching.
People seem to mean different things by 'singular thought'. The target of my talk was the view that one can usefully understand the representational content of beliefs and other intentional states as attributing properties to individuals, without any intervening modes of presentation. This view is often associated with a certain interpretation of attitude reports: whenever we can truly say `S believes (or knows etc.) that A is F', where A is a name, then supposedly the subject S stands in an interesting relation of belief (or knowledge etc.) to a proposition directly involving the bearer of that name.
I'm not denying that one can define some such concept of singular content. But I doubt it has any interesting use. In my talk, I argued that it is not useful for epistemology.
By `epistemology', I mean the systematic study of what we can know and how we can come to know it. Do we know that carbon emissions cause climate change? If so, what is the relevant evidence, and how does it support that conclusion? If not, what is missing? What would we have to discover? How can we find out if vaping causes cancer? How should a doctor diagnose a patient based on their symptoms? I take these kinds of questions to be central to epistemology, although they are more commonly discussed in confirmation theory than in old-fashioned epistemology classes.
I raised three worries about doing epistemology with singular content. I suspect the worries are well known, but I couldn't see them mentioned or addressed in the literature I skimmed.
The first worry draws on the context-sensitivity of attitude reports. Suppose I draw a card from a deck, face down. Suzy is watching. She doesn't know which card I've drawn. She does know that my favourite card in this deck is the Ace of Diamonds. I happen to have drawn that card. Now Suzy leaves the room. Pointing at the face-down card, I exclaim:
(*) "Suzy doesn't know that this is my favourite card."
That seems true. Then I turn around the card, and we all see it is the Ace of Diamonds. Pointing at the card again, I utter (*) again. Now what I say is intuitively false
So does Suzy know the singular proposition that the card in question is my favourite card? If we go by our practice of knowledge reports, the answer depends on which way around I hold the card. But Suzy isn't in the room, so the card's orientation makes no difference to Suzy's evidence.
The singularist doctrine therefore violates the following constraint on a sensible epistemology:
What Suzy knows is not sensitive to how I hold the card.
My second worry draws on the fact that names can be introduced by description. As Kripke and many others have pointed out, this seems to open the door to a priori knowledge of contingent facts. More generally, and more worryingly I think, it seems to allow acquiring knowledge without doing relevant research.
For example, if you know that someone invented the zip, you can introduce a name ('Julius') for that person. Now you know that Julius invented the zip. So you know the singular proposition that Witcomb L. Judson invented the zip.
For another example, suppose Donald Trump will not be impeached. If you know that Obama will not be impeached, you can introduce the name `Ronald' to denote Obama if Trump will be impeached and otherwise Obama. Now you know that Ronald will not be impeached. Assuming Trump will not be impeached, Ronald is Trump. So you know the singular proposition that Trump will not be impeached.
A sensible epistemology should not allow for such ways of gaining knowledge. It should respect the following principle:
If P is a contingent proposition about some subject matter (and one can rationally disbelieve P) then knowledge of P requires empirical enquiry into the relevant subject matter.
Relatedly, Alonzo Church once showed that every statement is logically equivalent to an identity statement. Let P be any proposition. Let `N' denote the set { x : x=0 & P }. Then P is true iff N = { 0 }. Now the singular proposition { 0 } = { 0 } is knowable a priori. If P is true, it is the same proposition as { 0 } = N. But we know that N = { x : x=0 & P }. Together, these entail P.
On the singularist view, all truths therefore follow logically from a priori truths. A sensible epistemology should deny this.
Many truths are not logically entailed by propositions that can be known without empirical enquiry.
My third worry is the one I care most about, in part because it does not rely on any tricks.
Consider Oscar from the Twin Earth story. According to friends of singular thought, Oscar knows the singular proposition that there is water (H2O) in the lakes. But how could he know this, given that he hasn't done any chemical research? How does he know the stuff in the lakes isn't XYZ?
A sensible epistemology, I think should respect the following principle:
If two things A and B look the same, and you initially don't know whether you'll be confronting A or B, then you can't come to know that you're confronting A just by looking.
For example, you can't find out that a patient has disease A rather than B from their symptoms if the two diseases have the same symptoms.
One might respond that Oscar doesn't know that the stuff in the lakes is water rather than XYZ, because he doesn't even have the concept of XYZ. I don't think this addresses the worry. But in any case, we can easily adjust the story.
Suppose we show Oscar a cup of XYZ and tell him that it contains twin water. (We may or may not tell him that twin water is not water, I don't think it matters.) Now Oscar knows the singular propositions that H2O is in the lakes and that XYZ is in the cup. I want to know how he could have that knowledge. How does he know it's not the other way round? What is his evidence?
Well, you might respond, when Oscar looks at the lakes, he sees water, and not XYZ. Perceptual experience provides singular evidence.
But it doesn't. Suppose I tell you that I'm going to pour a dark red liquid into a cup. I have a number of such liquids to chose from, and haven't yet made the choice. On the current proposal, by looking into the cup, you will come to know the singular proposition that liquid ABC is in the cup, where ABC is the substance I'll actually choose. If you value knowledge, you should therefore pay for an opportunity to look into the cup. That's absurd.
If you already know that a cup contains a dark red liquid, you make no relevant epistemic progress concerning the nature of the liquid by looking into the cup.
My worry is not so much that the singularist doctrine has counter-intuitive consequences. My worry is that denying all the displayed assumptions is incompatible with any systematic account of what kind of research we need to undertake to acquire specific knowledge about the world.
Regarding your first worry, when the card is face down you are talking about that card, the physical object, and Suzy did not know that it was the Ace, your favorite; but when it is face up you are talking about that card, the Ace, and Suzy did know that it was your favorite. What you are talking about depends on whether it is face up or face down. So there just seems to be an ambiguity about the meaning of "card" here.
Your second worry means little to me, as I do not hold to such theories of names; but I like your third worry. Similarly (as I blogged about a while back, having been thinking about Twin Earth), there seems to be the logical possibility of an exact copy of you. We simply assume that we are not being swapped instantaneously with such copies. We certainly cannot find out that we are not being so swapped empirically, as they would be exactly like us. And it does matter when it comes to reference and knowledge. If I see a copy of you waiting for a bus then I cannot know that you are waiting for a bus because you are not. And if I see you waiting for a bus then I can know that you are waiting for a bus even though I cannot possibly rule out it being your copy. This seems to make a mess of all of our reference and knowledge, until you realize that we simply assume that such swapping never does take place. That assumption is a hinge proposition (as Wittgenstein described such things). No?