I’m off for a few days while I head over to
Amsterdam for Christmas. I will be back early in the New Year with hopefully some slightly more polished things to say about modus ponens failures, Dr. Evil and countable additivity, privileged access and narrow content, and, it being unavoidable in January and February, philosophical gossip. (Though I can’t promise that the gossip will be polished – I half think I should promise that it will not be.) Happy holidays all, and good luck to everyone going on
the job market!

I was updating a few links when I discovered
something I didn’t really expect to find out during a regular webcrawl. If you crawl
on over to John
Hawthorne’s CV, and scroll not too far down, you’ll see that he has a paper
forthcoming in The Monist, co-authored
with me. This is very
exciting news, especially to me!

Despite the somewhat incredulous tone of the last
paragraph, I was more or less aware that the
paper was more or less likely to appear,
so it wasn’t like I had a paper accepted at a journal with no knowledge of it
(and in fact I even have a draft
of the paper available) but it still wasn’t exactly how I expected to get
confirmation of another publication. I wonder if news of its acceptance is official
enough to put on this year’s annual report?

In other co-authoring news, it looks likely that
the paper Andy Egan and I wrote on pranks
will be presented at the Symposium
on Theoretical and Applied Ethics at LSU next February. I think it’s my
duty to play this up for all it’s worth – it’s only fair that adding a few
jokes to a good idea for a paper that someone else (i.e. Andy) had gets me to
count as an ethicist. I’m not sure why it’s fair, but
now that I’m an Ethicist, I can just say that it’s fair and that’s already got
some evidential weight.

Well, here’s
something you don’t see every day. The review in Notre Dame Philosophical
Reviews of Beyond
Rigidity takes Soames to task for not being Millian enough. That’s the kind
of thing that happens in any field when you stake out an extreme position early
on, any subsequent movement back towards the middle ground will be interpreted
as betrayal by someone 😉

Well, here’s
something you don’t see every day. The review in Notre Dame Philosophical
Reviews of Beyond
Rigidity takes Soames to task for not being Millian enough. That’s the kind
of thing that happens in any field when you stake out an extreme position early
on, any subsequent movement back towards the middle ground will be interpreted
as betrayal by someone 😉

There are about a
million other things I should be doing right now, so it’s probably time to say
something more about Dr. Evil. I
knew that deep down one of the reasons I disliked approaches to probability
based on principles of indifference was that they threatened to collapse the
important distinction between risk and uncertainty. What I hadn’t realised,
until very recently, was Adam’s argument for his indifference principle involves
just such a collapse at one point.

First some
background. To my mind, what should have been a very important discovery in
early 20^th century work on probability was that there is a
distinction between risk and uncertainty. Here’s how Keynes introduces the
concept of uncertainty in an article from 1937 (“The General Theory of Employment”
Quarterly Journal of Economics).

By ‘uncertain’
knowledge, let me explain, I do not mean merely to distinguish what is known
for certain from what is only probable. The game of roulette is not subject, in
this sense, to uncertainty; nor is the prospect of a Victory bond being drawn.
Or, again, the expectation of life is only slightly uncertain. Even the weather
is only moderately uncertain. The sense in which I am using the term is that in
which the prospect of a European war is uncertain, or the price of copper and
the rate of interest twenty years hence, or the obsolescence of a new
invention, or the position of private wealth owners in the social system in
1970. About these matters there is no scientific basis on which the for any
calculable probability whatever. We simply do not know. Nevertheless, the
necessity for action and decision compels us as practical men to do our best to
overlook this awkward fact and to behave exactly as we should if we ha behind
us a good Benthamite calculation of a series of
prospective advantages and disadvantages, each multiplied by its appropriate
probability, waiting to be summed.

I think this is
all incredibly important, and any theory that ignores the distinction between
what is probable and what is genuinely uncertain is mistaken. Decisions based
on what is probable or improbable are grounded at least in well understood
principles about risk; decisions grounded in what is genuinely uncertain are
not. And I’m inclined to think that any theory that says that an agent’s attitude
to some uncertain propositions can be expressed by a single probability function
does ignore the distinction. This is especially true for theories that say this
about ideal agents.

This is hardly an
original thought. It was the basis of Keynes’s theory of probability outlined
in his dissertation of 1909, which eventually became the Treatise on Probability of 1921. Keynes had the probability, which
for him was just rational credence, of an uncertain proposition be a
non-numerical value. Ramsey criticised this on the grounds that probability
values are meant to enter into computations, according to the theory we can add
and multiply them, for example, and we don’t know how to add and multiply
non-numerical values. In my dissertation, I proposed that the theory that holds
that the credal states of a rational agent can be
represented by a set of probability functions rather than just a single
probability function could capture all of Keynes’s insights without being
vulnerable to Ramsey’s objection. This is not a new theory, it has been
discussed by Isaac Levi (“Ignorance, Probability and Rational Choice” 1982) Richard
Jeffrey (“Bayesianism with a Human Face” 1983), Bas
van Fraassen (“Figures in a Probability Landscape”
1990) and extensively by Peter Walley (Statistical Reasoning With Imprecise
Probabilities 1991), and in Walley’s case there’s
some connection drawn to Keynes’s work, so I still don’t want to make any dramatic claims to originality.

We draw a
connection between Keynes’s theory and these new theories by identifying the
probability of a proposition p as a
function from members of S, the set
of probability functions that represents the credal
states of an ideal agent, to [0, 1], where the value of the function is
the value of P(p) according to each P in
S. For most purposes we can simplify
this by saying the probability of p
is the range of that function. Then p
has a numerical probability in Keynes’s sense iff its probability is a singleton,
it is uncertain otherwise. Arguably the range of the function should always be
an interval (well, I argue for this at any rate) and if so we can say p is more uncertain the larger that
interval is. This gives us a concept of comparative uncertainty, and with that
we can say that everything Keynes
says in the above quote is true.

Now one of the
surprising things about interpreting Keynes’s term ‘uncertainty’ this way is
that a proposition can become more uncertain as we acquire more evidence about
it. Keynes seemed to think this was impossible, but here I think he was just
mistaken about the behaviour of some of his own concepts. (We all make
mistakes.) Here’s a case where just that happens. (As it turns out, it’s a case
I’ve written about. See my “Keynes,
Uncertainty and Interest Rates” Cambridge
Journal of Economics 2000).

I’m watching a
roulette game going on, and in particular paying close attention to one player,
called Kim. It’s a crowded room, so I can’t see the roulette wheel, or the
board where bets are placed, but I can see the croupier, and I can see Kim. I see
Kim place a bet on either red or black (I can see that from where she’s leaning
over the table) but I can’t tell which. And I have no evidence that tells me
one way or the other. I know from prior observation that this is a fair
roulette wheel. And I can see that the croupier is about to spin the wheel. Now
consider the following propositions. (For simplicity we’ll assume it’s a
roulette wheel with no green slots – this makes the example rather unrealistic,
but simplifies the computations no end without having any major philosophical
costs.)

kr = Kim bet on red
kb = Kim bet on black
br = The
ball lands on red
bb = The ball lands on black
 h
= Kim is happy in a few seconds

At this stage, I
think I can assign numerical probabilities in the following cases:

1. P(h
| kr Ù br) = 1
2. P(h | kr Ù bb)
= 0
3. P(h | kb Ù bb)
= 1
4. P(h | kb Ù br) = 0
5. P(br | kr) = ½  
6. P(bb | kr)
= ½
7. P(br | kb) = ½
8. P(bb | kb) = ½

Also note {kr, kb} and {br, bb} are partitions, and my credences reflect that (e.g. P(kr Ú kb) = 1.)

What I can’t do is
assign a numerical probability to kr or to kb, they
are just uncertain. Perhaps they’re not so uncertain that their probability is
[0, 1] – that’s what happens when a proposition is completely uncertain,
but they are uncertain to a degree.

Now I wait a few
seconds, and see that when the wheel stops, Kim is happy. So I update my
credences accordingly. What should my new credences be? Some may suggest that
my credences in br,
bb and bg should be unchanged, because I
have no new evidence that is relevant to their assessment. But this must be
false. For if it were true, I could do the following computations (11 and 12
are background, the new assumptions come in at 13 and 14).

11. P(br) = ½ from 5 and 7
12. P(bb) = ½ from 6 and 8
13. P(br | h) = ½ by assumption
14. P(bb | h) = ½
by assumption
15. P(kr | h) = P(kr Ù br | h)
by 2
16. P(kr Ù br | h) = P(br | h) by 4
17. P(kr | h) = ½ by 13, 15 and 16
18. P(kb | h) = ½
by identical reasoning to the last three lines
19. P(br | Øh) =
½ (since by 11 and 13 br
and h are independent)
20. P(bb | Øh) = ½ (since
by 12 and 14 bb and h are independent)
21. P(kr | Øh) =
½ (by equivalent reasoning to 15-17, with just the relevant appeals changed)
22. P(kr) = ½ by 17 and 21

And 22 is just
what we said we couldn’t conclude, because we weren’t in a position to assign
numerical probabilities to kr and kb. So the
simple assumption that we shouldn’t change our credences in br and bb when we learn h must
have been mistaken. What should happen is that after learning h, br and bb should go from being not at all uncertain to being rather
uncertain, in fact exactly as uncertain as kr and kb were (and I guess still are).

This is contentious,
but I think that the same thing is going on in Adam’s main argument. (I.e. it’s
contentious that it’s the same thing.) Here are the main examples again.

TOSS&DUPLICATION After Al goes
to sleep, researchers toss a coin that has a 10% chance of landing heads. Then
(regardless of the toss outcome) they duplicate Al. The next morning, Al and the duplicate
awaken in subjectively indistinguishable states.

Adam wants to
argue that in this case when Al wakes up his credence in HEADS should be 1/10.
A crucial premise in the argument for this is that P(HEADS/HeadsAl
or TailsDup) (TailsDup is
the proposition that he’s the duplicate and the coin landed tails – you can
figure out the rest of the code from that) is also 1/10. And he argues for that
as follows.

COMA As in TOSS&DUPLICATE, the
experimenters toss a coin and duplicate Al. But the following morning, the
experimenters ensure that only one person wakes up: If the coin lands heads, they allow Al to wake up (and put the
duplicate into a coma); if the coin lands tails, they allow the duplicate to
wake up (and put Al into a coma)

Suppose that in the COMA case, Al
gets lucky: the coin lands heads, and so the experimenters allow him to awaken.
Upon awakening, Al is immediately in a position to assert “Either I am Al and
the coin landed heads, or else I am the duplicate and the coin landed tails”.
So when Al wakes up in the COMA case, he has just the evidence about the coin
toss as he would have if he had been awakened in TOSS&DUPLICATE and then been told [HeadsAl
or TailsDup]. So to defend (3)—to show that in the
latter case Al’s credence in HEADS ought to be 10%—it is enough to show that when
Al wakes up in the COMA case, his credence in HEADS ought to be 10%.9 Let me
argue for that claim now.

Before Al was put to sleep, he was
sure that the chance of the coin landing heads was 10%,
and his credence in HEADS should have accorded with this chance: it too should
have been 10%. When he wakes up, his epistemic situation with respect to the
coin is just the same as it was before he went to sleep. He has neither gained
nor lost information relevant to the toss outcome. So his degree of belief in
HEADS should continue to accord with the chance of HEADS at the time of the
toss. In other words, his degree of belief in HEADS should continue to be 10%.

Adam considers an
objection that Al’s memories should give him evidence that he’s Al, and hence given
HeadsAl or TailsDup, he
should have a very high credence in HEADS. He responds as follows:

That’s all
wrong. TRUST YOUR MEMORIES, AL makes the same mistake that TRUST YOUR MEMORIES,
O’LEARY does. While it is true that in the absence of defeating auxiliary
beliefs, one ought to trust one’s memories, when Al wakes up he does have defeating auxiliary beliefs. He is sure that—whatever
the  outcome of the coin toss—someone was to wake up in just the
subjective state he is currently in. As far the outcome of the coin toss goes,
the total evidence Al has when he wakes up warrants exactly the same opinions
as the total evidence he had when he went to sleep.

This is what I
think is wrong. Adam is concerned to reject the line of reasoning that memories
provide evidence, because he thinks that they’re really only q-memories and
they don’t count for very much. But this ignores a crucial point I think. Al
doesn’t know whether his memories are real memories or mere q-memories. But
Adam thinks that he can assign a very precise credence to their being real: in
this case exactly 1/10. I don’t think this is true, and I think the only way
you’d come to infer it is by more or less presupposing an indifference
principle.

I’d put the
dialectic as follows. Al has some memories. These are actually conclusive
evidence that HEADS, though of course Al doesn’t know this. In fact he has no
idea whatsoever what the evidential force of those memories is. But that doesn’t
mean he should act as if they have no evidential value at all – if he does he’s
drawing a substantive conclusion, that q-memories have no evidential value from
premises that are essentially worthless, that he has no idea how much
evidential worth they have. (Substantive and, we might as well note, false.) He
should act like he has no idea how valuable the evidence is, just like in the
casino case I should act like I have no idea what the evidential force of h is. In that case I go from regarding br as risky to
regarding it as uncertain. I think Al’s attitude towards HEADS should be the
same in COMA. And if it is, the argument for the indifference principle in the Dr. Evil
paper fails.

There are about a
million other things I should be doing right now, so it’s probably time to say
something more about Dr. Evil. I
knew that deep down one of the reasons I disliked approaches to probability
based on principles of indifference was that they threatened to collapse the
important distinction between risk and uncertainty. What I hadn’t realised,
until very recently, was Adam’s argument for his indifference principle involves
just such a collapse at one point.

First some
background. To my mind, what should have been a very important discovery in
early 20^th century work on probability was that there is a
distinction between risk and uncertainty. Here’s how Keynes introduces the
concept of uncertainty in an article from 1937 (“The General Theory of Employment”
Quarterly Journal of Economics).

By ‘uncertain’
knowledge, let me explain, I do not mean merely to distinguish what is known
for certain from what is only probable. The game of roulette is not subject, in
this sense, to uncertainty; nor is the prospect of a Victory bond being drawn.
Or, again, the expectation of life is only slightly uncertain. Even the weather
is only moderately uncertain. The sense in which I am using the term is that in
which the prospect of a European war is uncertain, or the price of copper and
the rate of interest twenty years hence, or the obsolescence of a new
invention, or the position of private wealth owners in the social system in
1970. About these matters there is no scientific basis on which the for any
calculable probability whatever. We simply do not know. Nevertheless, the
necessity for action and decision compels us as practical men to do our best to
overlook this awkward fact and to behave exactly as we should if we ha behind
us a good Benthamite calculation of a series of
prospective advantages and disadvantages, each multiplied by its appropriate
probability, waiting to be summed.

I think this is
all incredibly important, and any theory that ignores the distinction between
what is probable and what is genuinely uncertain is mistaken. Decisions based
on what is probable or improbable are grounded at least in well understood
principles about risk; decisions grounded in what is genuinely uncertain are
not. And I’m inclined to think that any theory that says that an agent’s attitude
to some uncertain propositions can be expressed by a single probability function
does ignore the distinction. This is especially true for theories that say this
about ideal agents.

This is hardly an
original thought. It was the basis of Keynes’s theory of probability outlined
in his dissertation of 1909, which eventually became the Treatise on Probability of 1921. Keynes had the probability, which
for him was just rational credence, of an uncertain proposition be a
non-numerical value. Ramsey criticised this on the grounds that probability
values are meant to enter into computations, according to the theory we can add
and multiply them, for example, and we don’t know how to add and multiply
non-numerical values. In my dissertation, I proposed that the theory that holds
that the credal states of a rational agent can be
represented by a set of probability functions rather than just a single
probability function could capture all of Keynes’s insights without being
vulnerable to Ramsey’s objection. This is not a new theory, it has been
discussed by Isaac Levi (“Ignorance, Probability and Rational Choice” 1982) Richard
Jeffrey (“Bayesianism with a Human Face” 1983), Bas
van Fraassen (“Figures in a Probability Landscape”
1990) and extensively by Peter Walley (Statistical Reasoning With Imprecise
Probabilities 1991), and in Walley’s case there’s
some connection drawn to Keynes’s work, so I still don’t want to make any dramatic claims to originality.

We draw a
connection between Keynes’s theory and these new theories by identifying the
probability of a proposition p as a
function from members of S, the set
of probability functions that represents the credal
states of an ideal agent, to [0, 1], where the value of the function is
the value of P(p) according to each P in
S. For most purposes we can simplify
this by saying the probability of p
is the range of that function. Then p
has a numerical probability in Keynes’s sense iff its probability is a singleton,
it is uncertain otherwise. Arguably the range of the function should always be
an interval (well, I argue for this at any rate) and if so we can say p is more uncertain the larger that
interval is. This gives us a concept of comparative uncertainty, and with that
we can say that everything Keynes
says in the above quote is true.

Now one of the
surprising things about interpreting Keynes’s term ‘uncertainty’ this way is
that a proposition can become more uncertain as we acquire more evidence about
it. Keynes seemed to think this was impossible, but here I think he was just
mistaken about the behaviour of some of his own concepts. (We all make
mistakes.) Here’s a case where just that happens. (As it turns out, it’s a case
I’ve written about. See my “Keynes,
Uncertainty and Interest Rates” Cambridge
Journal of Economics 2000).

I’m watching a
roulette game going on, and in particular paying close attention to one player,
called Kim. It’s a crowded room, so I can’t see the roulette wheel, or the
board where bets are placed, but I can see the croupier, and I can see Kim. I see
Kim place a bet on either red or black (I can see that from where she’s leaning
over the table) but I can’t tell which. And I have no evidence that tells me
one way or the other. I know from prior observation that this is a fair
roulette wheel. And I can see that the croupier is about to spin the wheel. Now
consider the following propositions. (For simplicity we’ll assume it’s a
roulette wheel with no green slots – this makes the example rather unrealistic,
but simplifies the computations no end without having any major philosophical
costs.)

kr = Kim bet on red
kb = Kim bet on black
br = The
ball lands on red
bb = The ball lands on black
 h
= Kim is happy in a few seconds

At this stage, I
think I can assign numerical probabilities in the following cases:

1. P(h
| kr Ù br) = 1
2. P(h | kr Ù bb)
= 0
3. P(h | kb Ù bb)
= 1
4. P(h | kb Ù br) = 0
5. P(br | kr) = ½  
6. P(bb | kr)
= ½
7. P(br | kb) = ½
8. P(bb | kb) = ½

Also note {kr, kb} and {br, bb} are partitions, and my credences reflect that (e.g. P(kr Ú kb) = 1.)

What I can’t do is
assign a numerical probability to kr or to kb, they
are just uncertain. Perhaps they’re not so uncertain that their probability is
[0, 1] – that’s what happens when a proposition is completely uncertain,
but they are uncertain to a degree.

Now I wait a few
seconds, and see that when the wheel stops, Kim is happy. So I update my
credences accordingly. What should my new credences be? Some may suggest that
my credences in br,
bb and bg should be unchanged, because I
have no new evidence that is relevant to their assessment. But this must be
false. For if it were true, I could do the following computations (11 and 12
are background, the new assumptions come in at 13 and 14).

11. P(br) = ½ from 5 and 7
12. P(bb) = ½ from 6 and 8
13. P(br | h) = ½ by assumption
14. P(bb | h) = ½
by assumption
15. P(kr | h) = P(kr Ù br | h)
by 2
16. P(kr Ù br | h) = P(br | h) by 4
17. P(kr | h) = ½ by 13, 15 and 16
18. P(kb | h) = ½
by identical reasoning to the last three lines
19. P(br | Øh) =
½ (since by 11 and 13 br
and h are independent)
20. P(bb | Øh) = ½ (since
by 12 and 14 bb and h are independent)
21. P(kr | Øh) =
½ (by equivalent reasoning to 15-17, with just the relevant appeals changed)
22. P(kr) = ½ by 17 and 21

And 22 is just
what we said we couldn’t conclude, because we weren’t in a position to assign
numerical probabilities to kr and kb. So the
simple assumption that we shouldn’t change our credences in br and bb when we learn h must
have been mistaken. What should happen is that after learning h, br and bb should go from being not at all uncertain to being rather
uncertain, in fact exactly as uncertain as kr and kb were (and I guess still are).

This is contentious,
but I think that the same thing is going on in Adam’s main argument. (I.e. it’s
contentious that it’s the same thing.) Here are the main examples again.

TOSS&DUPLICATION After Al goes
to sleep, researchers toss a coin that has a 10% chance of landing heads. Then
(regardless of the toss outcome) they duplicate Al. The next morning, Al and the duplicate
awaken in subjectively indistinguishable states.

Adam wants to
argue that in this case when Al wakes up his credence in HEADS should be 1/10.
A crucial premise in the argument for this is that P(HEADS/HeadsAl
or TailsDup) (TailsDup is
the proposition that he’s the duplicate and the coin landed tails – you can
figure out the rest of the code from that) is also 1/10. And he argues for that
as follows.

COMA As in TOSS&DUPLICATE, the
experimenters toss a coin and duplicate Al. But the following morning, the
experimenters ensure that only one person wakes up: If the coin lands heads, they allow Al to wake up (and put the
duplicate into a coma); if the coin lands tails, they allow the duplicate to
wake up (and put Al into a coma)

Suppose that in the COMA case, Al
gets lucky: the coin lands heads, and so the experimenters allow him to awaken.
Upon awakening, Al is immediately in a position to assert “Either I am Al and
the coin landed heads, or else I am the duplicate and the coin landed tails”.
So when Al wakes up in the COMA case, he has just the evidence about the coin
toss as he would have if he had been awakened in TOSS&DUPLICATE and then been told [HeadsAl
or TailsDup]. So to defend (3)—to show that in the
latter case Al’s credence in HEADS ought to be 10%—it is enough to show that when
Al wakes up in the COMA case, his credence in HEADS ought to be 10%.9 Let me
argue for that claim now.

Before Al was put to sleep, he was
sure that the chance of the coin landing heads was 10%,
and his credence in HEADS should have accorded with this chance: it too should
have been 10%. When he wakes up, his epistemic situation with respect to the
coin is just the same as it was before he went to sleep. He has neither gained
nor lost information relevant to the toss outcome. So his degree of belief in
HEADS should continue to accord with the chance of HEADS at the time of the
toss. In other words, his degree of belief in HEADS should continue to be 10%.

Adam considers an
objection that Al’s memories should give him evidence that he’s Al, and hence given
HeadsAl or TailsDup, he
should have a very high credence in HEADS. He responds as follows:

That’s all
wrong. TRUST YOUR MEMORIES, AL makes the same mistake that TRUST YOUR MEMORIES,
O’LEARY does. While it is true that in the absence of defeating auxiliary
beliefs, one ought to trust one’s memories, when Al wakes up he does have defeating auxiliary beliefs. He is sure that—whatever
the  outcome of the coin toss—someone was to wake up in just the
subjective state he is currently in. As far the outcome of the coin toss goes,
the total evidence Al has when he wakes up warrants exactly the same opinions
as the total evidence he had when he went to sleep.

This is what I
think is wrong. Adam is concerned to reject the line of reasoning that memories
provide evidence, because he thinks that they’re really only q-memories and
they don’t count for very much. But this ignores a crucial point I think. Al
doesn’t know whether his memories are real memories or mere q-memories. But
Adam thinks that he can assign a very precise credence to their being real: in
this case exactly 1/10. I don’t think this is true, and I think the only way
you’d come to infer it is by more or less presupposing an indifference
principle.

I’d put the
dialectic as follows. Al has some memories. These are actually conclusive
evidence that HEADS, though of course Al doesn’t know this. In fact he has no
idea whatsoever what the evidential force of those memories is. But that doesn’t
mean he should act as if they have no evidential value at all – if he does he’s
drawing a substantive conclusion, that q-memories have no evidential value from
premises that are essentially worthless, that he has no idea how much
evidential worth they have. (Substantive and, we might as well note, false.) He
should act like he has no idea how valuable the evidence is, just like in the
casino case I should act like I have no idea what the evidential force of h is. In that case I go from regarding br as risky to
regarding it as uncertain. I think Al’s attitude towards HEADS should be the
same in COMA. And if it is, the argument for the indifference principle in the Dr. Evil
paper fails.

I’ve had a few complaints about the way
pictures work on the blog, so I’ve deleted the posts
involving graphics. So from now on it’ll just have to be me talking. That might
not be a good thing, but we’ll see.

In
both my recent notes on indifference principles, the comments on Nick Bostrom’s
computer simulation paper and Adam Elga’s Dr Evil paper, I’ve mentioned that
the proponents of these theories assume a theory of evidence that is
intuitively quite plausible, and may have been the mainstream view not long
ago, and may even be ultimately true, but which is not very popular among
philosophers of perception these days. I didn’t think much followed from this,
save perhaps that those presupposing a theory that is widely viewed as being
hopelessly befuddled owe us an explanation as to why they are sticking with it.
And in this little endeavour I have been utterly unsuccessful. This could be
because my heart hasn’t really been in it due to underlying internalist sympathies,
or because I’m wrong that the indifferentists need to address this, or because
I’m no good at convincing people of things, or because of any number of other
reasons. Suffice to say that in some circles, the idea that when we look at a
hand we have evidence of an epistemically different kind to a brain-in-a-vat
that is stimulated in the way our brains are when we look at a hand is not
viewed as being particular plausible.

When
in trouble in a case like this, call in the heavy hitters. Alex Byrne has a paper
forthcoming in Noûs in which he
argues that the sceptical
paradoxes are not really deep paradoxes. By this he means, in part, that
there isn’t anything like a compelling argument for scepticism. And this is because
he thinks that the canonical arguments for scepticism turn out to rest on very
implausible premises on close inspection. One of those premises is that
perceptual evidence underdetermines what the external world is like: we could
have just this evidence and be dreaming (or a brain-in-a-vat, etc.). This,
Byrne thinks, can be shown to be false simply by carefully reflecting on the nature
of evidence. The whole paper is worth reading, but let me just extract a few
choice quotes.

          The
known (evidence) proposition e has yet to be identified. [Byrne has just
argued that evidence should be propositional. The challenge is to determine
whether there is any candidate to be e that is compatible with
thorough-going external world scepticism.]The candidates may be divided into
two classes. The first—class I— consists of propositions about S’s sense-data,
ideas, impressions, phantasms or other queer entities allegedly “given” in
experience. The second—class II—consists of propositions about how things look
or (visually) appear to S (cf. the first paragraph of this section [not
excerpted here.]).

          It
is quite doubtful that (trivial exceptions aside) any propositions in class I
are true, a fortiori known; they may accordingly be dismissed. This
would have sounded dogmatic as recently as the first half of the twentieth
century: it is only in the last fifty years or so that the deep flaws in what
used to be called the “representative theory of perception” have become
gradually visible. Admittedly, not everyone agrees that the theory rests on a
soggy bog of error: in one form or another, it still has its defenders. However,
it is unnecessary here to rehash the argument: because we are playing the first
sceptical game, the sceptic must steer clear of philosophical controversy.

          That
leaves the members of class II: propositions about how things look or appear to
S—in other words, certain propositions about S’s mental states.
But because the representative theory of perception is off-limits, there is
very little motivation for thinking that one’s knowledge of the external world
rests on a foundation of knowledge about one’s own psychology…

          Propositions
about how things look or appear to S can be divided into two types. The
first—type II_E—comprises external world propositions,
because they entail the existence of o: that o looks square to S,
that it appears to S that o is square, etc. Hence, propositions
of type II_E, despite not entailing p, and perhaps being
known by S, are quite unsuitable candidates to be e. For e is
not supposed to be an external world proposition.

          The
second—type II_I—comprises those propositions about how
things look or appear to S that are not external world propositions (or
so we may suppose): that it appears to S that (some x) x is
square, that it appears to S that the F is square (for various fillings
for ‘F’, e.g. ‘tile’, ‘pink thing’), etc. If e is to be found in
class II, it must be of type II_I.

          [I]t
is not plausible that e is a type II_I proposition.
First, these propositions have to be true; clearly we need not suppose
that it appears to S that the tile, or the pink thing, is
square. But is it even clear that it must appears to S that (some x)
x is square? If not, then since there are no better candidates, e is
not a type III proposition. Second, S believes e, and it is
quite unobvious why S, if he is to know p via his senses, must
have any beliefs about how things appear, let alone believe one of the
specific propositions under consideration. Suppose S is a conceptually
challenged animal who cannot entertain these comparatively sophisticated
thoughts about appearances; does this fact alone imply that S cannot use
his eyes to come to know that o is square?

In
both my recent notes on indifference principles, the comments on Nick Bostrom’s
computer simulation paper and Adam Elga’s Dr Evil paper, I’ve mentioned that
the proponents of these theories assume a theory of evidence that is
intuitively quite plausible, and may have been the mainstream view not long
ago, and may even be ultimately true, but which is not very popular among
philosophers of perception these days. I didn’t think much followed from this,
save perhaps that those presupposing a theory that is widely viewed as being
hopelessly befuddled owe us an explanation as to why they are sticking with it.
And in this little endeavour I have been utterly unsuccessful. This could be
because my heart hasn’t really been in it due to underlying internalist sympathies,
or because I’m wrong that the indifferentists need to address this, or because
I’m no good at convincing people of things, or because of any number of other
reasons. Suffice to say that in some circles, the idea that when we look at a
hand we have evidence of an epistemically different kind to a brain-in-a-vat
that is stimulated in the way our brains are when we look at a hand is not
viewed as being particular plausible.

When
in trouble in a case like this, call in the heavy hitters. Alex Byrne has a paper
forthcoming in Noûs in which he
argues that the sceptical
paradoxes are not really deep paradoxes. By this he means, in part, that
there isn’t anything like a compelling argument for scepticism. And this is because
he thinks that the canonical arguments for scepticism turn out to rest on very
implausible premises on close inspection. One of those premises is that
perceptual evidence underdetermines what the external world is like: we could
have just this evidence and be dreaming (or a brain-in-a-vat, etc.). This,
Byrne thinks, can be shown to be false simply by carefully reflecting on the nature
of evidence. The whole paper is worth reading, but let me just extract a few
choice quotes.

          The
known (evidence) proposition e has yet to be identified. [Byrne has just
argued that evidence should be propositional. The challenge is to determine
whether there is any candidate to be e that is compatible with
thorough-going external world scepticism.]The candidates may be divided into
two classes. The first—class I— consists of propositions about S’s sense-data,
ideas, impressions, phantasms or other queer entities allegedly “given” in
experience. The second—class II—consists of propositions about how things look
or (visually) appear to S (cf. the first paragraph of this section [not
excerpted here.]).

          It
is quite doubtful that (trivial exceptions aside) any propositions in class I
are true, a fortiori known; they may accordingly be dismissed. This
would have sounded dogmatic as recently as the first half of the twentieth
century: it is only in the last fifty years or so that the deep flaws in what
used to be called the “representative theory of perception” have become
gradually visible. Admittedly, not everyone agrees that the theory rests on a
soggy bog of error: in one form or another, it still has its defenders. However,
it is unnecessary here to rehash the argument: because we are playing the first
sceptical game, the sceptic must steer clear of philosophical controversy.

          That
leaves the members of class II: propositions about how things look or appear to
S—in other words, certain propositions about S’s mental states.
But because the representative theory of perception is off-limits, there is
very little motivation for thinking that one’s knowledge of the external world
rests on a foundation of knowledge about one’s own psychology…

          Propositions
about how things look or appear to S can be divided into two types. The
first—type II_E—comprises external world propositions,
because they entail the existence of o: that o looks square to S,
that it appears to S that o is square, etc. Hence, propositions
of type II_E, despite not entailing p, and perhaps being
known by S, are quite unsuitable candidates to be e. For e is
not supposed to be an external world proposition.

          The
second—type II_I—comprises those propositions about how
things look or appear to S that are not external world propositions (or
so we may suppose): that it appears to S that (some x) x is
square, that it appears to S that the F is square (for various fillings
for ‘F’, e.g. ‘tile’, ‘pink thing’), etc. If e is to be found in
class II, it must be of type II_I.

          [I]t
is not plausible that e is a type II_I proposition.
First, these propositions have to be true; clearly we need not suppose
that it appears to S that the tile, or the pink thing, is
square. But is it even clear that it must appears to S that (some x)
x is square? If not, then since there are no better candidates, e is
not a type III proposition. Second, S believes e, and it is
quite unobvious why S, if he is to know p via his senses, must
have any beliefs about how things appear, let alone believe one of the
specific propositions under consideration. Suppose S is a conceptually
challenged animal who cannot entertain these comparatively sophisticated
thoughts about appearances; does this fact alone imply that S cannot use
his eyes to come to know that o is square?

Kieran
Healy writes on the (slow-)growing controversy over the role of intuitions
in philosophy. For background, see the papers by Jonathan Weinburg et
al here,
here
and here. (If you haven’t seen the survey results about intuitions on Gettier cases across cultural and social groups in these papers yet, you should. And prepare to be a little suprised.)
Kieran has a rather funny caricature of the way philosophers (or at least
metaphysicians) generally argue, but then goes off on a riff about why we
should care more about where intuitions come from.

In the meantime, you might be interested in looking at other writers, who
have explored the
idea that our intuitions might have institutional
roots; that culture might mold conceptions
of rationality and thus deeply affect
how you think; that classification
is a social process which might have its origins in
material life; and that although individual and social cognition interact in
complex ways, getting socialized into a culture often implies subscribing
to its point of view.

I’m
not sure how any of this undercuts the use philosophers make of intuitions. It
seems to me that even if we acknowledge all of this, there are still epistemological
and metaphysical reasons to use intuitions in philosophy. (You
mean you’ll be defending philosophy by using more philosophy? Yeah,
well what did you expect me to use, chemistry or something?)

The
epistemological reason is that for each of these facts about intuition, we
could (I think) find an equally
disturbing fact about perception. How we see the world around us is affected by
the kind of culture we’re in, what we expect to find and so forth. But none of
that implies that we should stop trusting perceptions as a source of evidence,
provided we’re suitably careful about how we employ them. Of course, practically
nothing should stop us trusting perception as a source of
evidence; that way lies madness, if not philosophical
immortality.

The
metaphysical reason is that intuitions are sometimes constitutive of the
concepts we’re aiming to analyse. Want to know what’s a house? Well, presumably
houses are things that satisfy the predicate “house”, or fall under the concept
HOUSE. And presumably the facts about what makes an object satisfy the
predicate “house” include facts about how the term “house” gets the meaning it
gets in the language we speak. And presumably those facts include facts about
the intuitions people have about houses. A similar story is probably true for
the concept HOUSE, though here there are some more prominent
dissenters. Now it’s rather controversial whether a similar story could be
true if we replaced “house” with “item of knowledge”, or “rational belief”, or “mind”,
or “person”, or “just act”, or (I guess most controversially) “object”, but at
least for terms towards the left of that list, it seems plausible enough.