## 1. Skeptical Hypotheses and the Skeptical Argument



The Cartesian Skeptic describes an alleged logically possible scenario
in which our mental lives and their histories are precisely the same
as what they actually are, but where the causes of the facts about our
mental lives are not the kinds of events in the external world that we
commonly think they are. On Descartes' Evil Genius hypothesis,
there is no physical world. Rather you are a disembodied mind, and
your entire mental life, with all of its experiences, has been caused
by an all-powerful, purely spiritual Evil Genius. As a result, your
beliefs about the external world, such as that you have a body, or
that there are planets in the solar system, are all mistaken. On the
brain-in-a-vat hypothesis, a given person is a disembodied brain
living in a vat of nutrients. The nerve endings of the brain are
connected to a supercomputer, whose program sends electrical impulses
that stimulate the brain in the same way that actual brains are
stimulated when perceiving external objects. If you are a brain in a
vat, suppose, your conscious experiences are and have been
qualitatively indistinguishable from the experiences you have had over
the entire course of your mental life. But if as the result of your
computer-caused experiences you believe, say, that you have a body,
then you are mistaken.



Given such an hypothesis as that of the brain-in-a-vat, the skeptic
can go on to argue that there are many commonsense beliefs that we
think we know, but that we do not in fact know. One common such
argument is based on the widely endorsed closure principle that
*knowledge is closed under known entailments*:


* (CL) For all persons
*S* and propositions *p* and *q*, if *S* knows
that *p*, and *S* knows that *p* entails *q*, then
*S* knows that *q*.



Now pick any proposition about the external world that you think you
know to be true but that is inconsistent with your being a brain in a
vat, say, the proposition that you have a body. Then the skeptic can
argue as follows:


* (SA)
(1)
 You know that the proposition that you have a
body entails that you are not a brain in a vat. [Premise]
* [?] (2) 
If you know that you have a body, then you know that
you are not a brain in a vat. [By (1) and (CL)]
* (3) 
But you don't know that you are not a brain in a
vat. [Premise]
* [?] (4) 
You don't know that you have a body. [By (2) and
(3)]



Premise (3) seems justified by the fact that you have the same
conscious experiences whether you are a normal human in a normal
physical world or a brain in a vat. For again, the evidence you have
for each alternative is exactly the same. So you don't know that
you're not a brain in a vat.


## 2. Putnam's Argument Against BIV-Skepticism



On Putnam's version of the brain-in-a-vat hypothesis, the
contents of the universe now and always have been relatively few.
There have existed and now exist only brains in vats of nutrients and
the supercomputers that send and receive messages to and from each
brain. Putnam's hypothesis assumes that each human (and each
sentient creature) that exists or has ever existed is one of the
brains in the vats. The supercomputers are so clever that their
electronic interactions with the brains result in exact duplications
of the mental lives and histories of each person whose brain is in a
vat. Thus I, you, indeed *we* (all human beings) are brains in
a vat on this hypothesis. Let us call a brain in a vat of this sort a
'BIV'.



Putnam's goal is to refute the skeptical argument that is based
on the BIV hypothesis, by providing a counterargument for the
conclusion that we are not BIVs. Thus, each of us is provided with a
way of *knowing* that she is not a BIV, contrary to premise (3)
of the skeptical argument (SA) above. The crucial move in
Putnam's argument is a sub-argument to the effect that that if
one were a BIV, one would not be able to grasp the meanings of various
general terms, such as 'tree', 'brain', and
'vat'. For in order for an utterance of 'tree'
for example to represent or refer to trees, Putnam maintains, there
must be some *causal connection* between uses of
'tree' and real trees (Putnam 1981 [1999: 37]). Following
Wright (1992: 71), I will call this 'the causal
constraint'. A similar point, Putnam assumes, holds for the
words 'brain' and 'vat', as well as for mental
utterances of, and the concepts expressed by, such words. It follows
that if we are BIVs, then since our uses of 'brain' and
'vat' do not bear the right causal relations to actual
brains and vats, we cannot so much as *think* or *say*
that we are brains in a vat (Putnam 1981 [1999: 31]).



Putnam goes on to suggest that while a BIV cannot think or say that
she is a brain in a vat, her utterances of 'BIV' could
refer to something *else*. For instance, the utterances could
refer to (i) BIVs-in-the-image. That is, the utterances could refer to
the succession of experiences as of being a BIV. In this case, the
BIV's utterance would just be *false*, since the computer
program would never allow her to have perceptual experiences as of
being an envatted brain as opposed to being an embodied person. (Of
course, a BIV could only *seem* to be uttering words. So we
should just identify her utterances with her mental
'seemings' to utter. See Putnam 1981 [1999: 31].)



In addition to 'brain-in-a-vat-in-the-image', Putnam
suggests (1981 [1999: 36]) two other possible sorts of things that
'brain in a vat' might refer to for a BIV. It might also
refer to (ii) the electronic impulses that cause experiences as of
being a BIV or perhaps to (iii) features of the computer program that
cause those electronic impulses. I will use the expressions
'brain\* in a vat\*' and 'BIV\*' to provide a
schematic representation of whichever of these three possible meanings
of 'BIV' in vat-English is correct, or if none is correct,
'brain\* in a vat\*' and 'BIV\*' represent the
meaning of 'BIV' in vat-English, whatever it is.



The important fact for Putnam's argument is that whichever of
these possible meanings is had in vat-English by 'I am a brain
in a vat', that sentence, as used by a BIV, will be
*false*. We saw that in sense (i), 'I am a brain in a
vat' would be false in vat-English, since a BIV would never have
(perceptual) experiences as of being a BIV. Putnam does not explain
why 'I am a brain in a vat' would be false in both senses
(ii) and (iii). Brueckner (2016: 4) suggests that since in sense (iii)
both 'brain' and 'vat' would refer to certain
computer program features, a BIV would not be a BIV in sense (iii): no
BIV would be a certain computer program feature that is "located
in" a certain other computer program feature. A similar point
would hold for sense (ii). From these considerations, Putnam then
concludes: "In short, if we are brains in a vat, then 'we
are brains in a vat' is false. So it is (necessarily)
false" (Putnam 1981 [1999: 37]). Here, Putnam seems to think
that he has shown the conclusion that he was aiming to show, namely,
that *we are not brains in a vat*. But in fact, the most he has
shown so far is that a BIV's utterance of 'We are not
brains in a vat' would be true. But this conclusion is simply
irrelevant to Putnam's goal, since as Putnam himself points out,
the BIV's utterance *does not mean* that we are not BIVs
(see Brueckner 1986: 152 and Forbes 1995 [1999: 63]).


## 3. The Disjunctive Argument



Various authors have noted that additional information is needed to
derive Putnam's desired conclusion ('I am not a brain in a
vat'). One of the earliest and most important of these
reconstructions was suggested by Anthony Brueckner (1986). He proposed
that Putnam's argument could reasonably be construed as an
instance of disjunction elimination (\(p \lor q\), \(p \rightarrow
r\), \(q \rightarrow r \vdash r\)) as follows:


* (B)  (1)
Either I am a BIV (speaking vat-English) or I am
a non-BIV (speaking English). [Premise]
* (2)  If
I am a BIV (speaking vat-English), then my
utterances of 'I am a BIV' are true iff I have sense
impressions as of being a BIV. [Premise]
* (3) 
If I am a BIV (speaking vat-English), then I do not
have sense impressions as of being a BIV. [Premise]
* [?] (4) 
If I am a BIV (speaking vat English), then my
utterances of 'I am a BIV' are false. [By (2), (3)]
* (5)  If
I am a non-BIV (speaking English), then my
utterances of 'I am a BIV' are true iff I am a BIV.
[Premise]
* [?] (6) 
If I am a non-BIV (speaking English), then my
utterances of 'I am a BIV' are false. [By (5)]
* [?] (7) 
My utterances of 'I am a BIV' are
false. [By (1), (4), (6)]



It is important to note, as Brueckner does, that (7) is not
Putnam's desired conclusion ('I am not a BIV'), nor
does it alone imply this conclusion, since (7) is consistent with the
speaker's being a BIV, in the English sense of
'BIV'.



To reach Putnam's conclusion, Brueckner considers use of the
following disquotation principle:


* (T) My utterances of
'I am not a BIV' are true iff I am not a BIV.



Note that (7) implies


* (8) My utterances of
'I am not a BIV' are true,



And (8) together with (T) apparently yield the desired anti-skeptical
conclusion: I am not a BIV.



But Brueckner persuasively argues (1986: 164-165) that using the
disquotational principle (T) in this context is illegitimate. In
effect, (T) as used in this context is *ambiguous* (see Folina
2016: 159). Depending on whether the speaker is or is not a BIV, (T)
will provide different truth conditions for the speaker's
utterances of 'I am not a BIV'. If the speaker is not a
BIV and thus is speaking English in uttering (T), then the truth
condition for 'I am not a BIV' is just the condition that
the speaker is not a BIV. But if the speaker is a BIV, then the truth
condition expressed by 'I am not a BIV' is the condition
that the speaker is not a BIV\*, where 'BIV\*' has the
vat-English meaning of 'BIV', whatever it is (perhaps one
of the three meanings that Putnam suggests). Note that on this
interpretation, the argument's conclusion (that the speaker is
not a BIV\*) is simply *irrelevant*, since Putnam's
desired conclusion is 'I am not a BIV' in its
*English* sense.



On the other hand, if the speaker is assumed to be speaking English in
using (T), then (T) together with (8) does imply the desired
anti-skeptical result 'I am not a BIV' in its English
sense. But, as Brueckner puts it in some later articles (1992, 2016),
this use of (T) just begs the question, since for the conclusion
('I am not a BIV') to be true in English, the speaker must
be speaking English in uttering the premise (T), and so must be a
non-BIV, which is of course the conclusion to be shown. As Brueckner
says, the argument 



> 
> 
> ... is *epistemically circular* in William Alston's
> sense: knowledge of one of its premises--(T)--requires
> knowledge of its conclusion [Alston 1989]. (Brueckner 2016: 4)
> 
> 
> 



Another way to see that the argument based on the English sense of (T)
would be question-begging is to ask whether a speaker would have
warrant to believe (T) in its English sense, if the speaker did not
*already* have warrant to believe that she was a non-BIV
speaking English. Note that if the speaker were a BIV speaking
vat-English, the speaker would not even *understand* (T) in its
English sense, let alone have warrant to believe it in that sense. So
it surely seems that the speaker could not have warrant to believe (T)
in its English sense unless she *already* had warrant to
believe the argument's conclusion, that is, had warrant to
believe 'I am not a BIV' in its English sense. (See
Brueckner 1986: 164-165 and 2016: 4. The type of
question-begging just described, as well as the type described by
Alston (1986 [1989]) would seem to be the same as the type identified
by Crispin Wright and that he describes as failure of warrant to
transmit from premise to conclusion. See Wright 1985: 436; 2000:
141-143; see also Davies 2000: 397-399.)



The proper conclusion to draw from Brueckner's seminal
discussion would thus seem to be that either the argument (B) plus (T)
has an irrelevant conclusion (if the speaker is assumed to be a BIV
speaking vat-English), or the argument begs the question (if the
speaker is assumed to be a non-BIV speaking English).



In later work Brueckner 1992 and 2003 seems to raise a problem for the
question-begging charge, when he points out that one can know that a
given disquotational principle expresses a truth whether one is a
non-BIV speaker of English or a BIV speaker of vat-English. We will
discuss this issue below in section 6.


## 4. The Semantic Argument



In later work on Putnam's anti-skeptical argument, especially in
his articles 1992 and 2003, Brueckner seems to have abandoned his
(1986) objection to uses of disquotation, such as the use of (T), in
various versions of Putnam's argument. In his 1992 Brueckner
proposes a general schema in which to formulate specific Putnamian
anti-skeptical arguments (1992 [1999: 48]):


* (I) If I am a BIV, then
my utterances of sentences have non-disquotational truth conditions
and express non-disquotational contents.
* (II) My utterances of
sentences have disquotational truth conditions and express
disquotational contents.
* (III) I am not a BIV.
[By I and II].



Brueckner calls this *the semantic argument*. As an instance of
the disquotational premise II, Brueckner considers (1992 [1999: 53]):



* (\*\*) My utterances of
'I am a BIV' are true iff I am a BIV.



Apparently as justification for use of (\*\*) in anti-skeptical
arguments, Brueckner notes:



> 
> 
> This statement of disquotational truth conditions for my utterances of
> 'I am a BIV' is guaranteed to express a truth as long as
> the metalanguage in which (\*\*) is stated contains the object language
> to which my utterance 'I am a BIV' belongs.
> 
> 
> 



So it seems that Brueckner has changed his mind from his 1986 and at
this point no longer believes that the use of disquotation in
Putnamian anti-skeptical arguments is question-begging. We will return
to this topic below.



But while seeming to accept disquotational premises, Brueckner now
sees serious problems with instances of the first premise-schema I. He
considers the following instance of I:


* (Cond) If I am a BIV,
then my utterances of 'I am a BIV' are true iff I am a
BIV\*,



where, as Brueckner puts it, "'I am a BIV\*'
formulates the Putnamian non-disquotational truth conditions, whatever
they are". (As Brueckner had explained earlier (1992 [1999:
47]), these truth conditions would be
"non-disquotational", since the metalanguage in which they
are stated does not contain the object language to which the
relevant BIV tokens of 'I am a BIV' belong.) Now for
(Cond) to be true, its consequent must be true when evaluated at a
vat-world. So consider the consequent of (Cond.):


* (Cons) My utterances of
'I am a BIV' are true iff I am a BIV\*.



According to Brueckner, since (Cons) is not disquotational, the
metalanguage in which it is expressed cannot contain the object
language to which utterances of 'I am a BIV' (as meant in
(Cons)) belongs. But then, Brueckner argues, (Cons) can express a
truth at a vat-world only if its speaker is not *in* a
vat-world. Here, Brueckner seems to reason that since the metalanguage
being used to express (Cons) does not contain the object language
being described (vat-English), the metalanguage being used is a
language spoken only by non-BIVs. Brueckner concludes, "we
apparently cannot, *without begging the question*, use premise
(I) of the anti-skeptical semantic argument" (1992 [1999: 55];
his italics).


## 5. Wright's Reconstruction.



Crispin Wright (1992: 74) suggested an important reconstruction of
Putnam's anti-skeptical argument which, like Brueckner's
original reconstruction, also essentially depends on disquotation:


* (i) My language
disquotes; [Premise]
* (ii) In BIVese,
'brain-in-a-vat' does not refer to brains-in-a-vat;
[Premise]
* (iii) In my language,
'brain-in-a-vat' is a meaningful expression; [Premise]
Hence,
* (iv) In my language,
'brain-in-a-vat' refers to brains-in-a-vat; [By (i) and
(iii)]
* (v) My language is not
BIVese; [By (ii) and (iv)]
* (vi) If I am a BIV,
then my language is BIVese; [definition of BIVese] So,
* (vii) I am not a
brain-in-a-vat.



Bob Hale (2000: 185) points out that the two premises (i) and (iii)
involving disquotation are both acceptable. Both 



> 
> 
> might be available to, and warranted for, a proponent of the argument,
> *regardless of whether she is or is not a
> brain-in-a-vat*.... (his italics) 
> 
> 
> 



However, Hale argues, provided that the speaker of premise (ii) is not
merely contradicting premise (i), she must *not* be using
'brain-in-a-vat' as a disquotation of
"'brain-in-a-vat'", as it occurs earlier in
(ii). Thus the speaker of (ii) must not be speaking BIVese, and so
must be a non-BIV. Hale concludes, 



> 
> 
> ... in taking premiss (ii) to be available to him, Putnam is in
> effect *assuming* that he is not a brain-in-a-vat. Since that
> is just what he is trying to prove, his argument is viciously
> circular. (2000: 186; his italics)
> 
> 
> 



Clearly, Hale's point provides a powerful objection to
Wright's reconstruction of Putnam's argument.


## 6. Disquotation Again.



Brueckner (2003: 156) considers the following argument:


* (A\*) If I am a BIV,
then it is not the case that my utterances of 'Trees are
green' are true iff trees are green.
* (B\*) My utterances of
'Trees are green' are true iff trees are
green.
* (C) So, I am not a
BIV.



In reply to the objection that use of the disquotational premise (B\*)
begs the question, Brueckner says that the objector would be right to
reject a defense of (B\*) that is based on the claim that since I know
that I'm a normal speaker of English, I also know (B\*). Such a
claim would indeed beg the question, Brueckner says. But he goes on to
suggest that knowledge of such disquotational facts as (B\*) need not
be based on knowledge that one is a normal English speaker. Rather,
the former kind of knowledge "is simply part of understanding my
own language (whatever it is and whatever I am)" (2003:
157).



In this reply, Brueckner seems to be relying on the fact that one can
know that (B\*) expresses a truth, whether or not one is a non-BIV
speaker of English or a BIV speaking vat-English. That is simply
because, whatever language is being spoken in uttering (B\*), the
metalanguage being used contains the object language sentence that
provides the relevant truth condition.



But as Brueckner himself had earlier pointed out (1986: 165; 1995:
100)), while we can in this manner know that disquotational sentences
like (B\*) are *true*, we cannot know *which* truth is
being expressed until we know which language is being spoken. In this
case, if the speaker is a BIV speaking vat-English, then (B\*) would
mean "My utterances of 'trees are green' are true
iff trees\* are green" (where 'trees\*' expresses one
of the three possible types of meanings that Putnam suggests for
'tree' in vat-English). So on the assumption that the
speaker is a BIV speaking vat-English, premise (B\*) would be true.
However, the conclusion (C) of the argument would then mean 'I
am not a BIV\*', and while this conclusion would also be true, it
is also irrelevant to Putnam's desired conclusion (in English)
'I am not a BIV'. Moreover, note that if understood to be
in vat-English, the premise (A\*) would be false.



On the other hand, if we assume that the speaker is a non-BIV speaking
English, then premises (A\*) and (B\*) would both be true, as would the
conclusion (C). However, the argument in question, though sound, would
blatantly beg the question. For in order for the speaker to have
warrant that premises (A\*) and (B\*) are both true in the relevant
senses, warrant must *already* be available to the speaker of
(A\*) and (B\*) that she is a non-BIV speaking English.



We should also note that premise (A\*) cannot be true if it is spoken
by a BIV speaking vat-English, since disquotation holds for
vat-English as well as English. Thus (A\*) is true only if spoken by a
non-BIV speaking English, and so its use begs the question for the
same reason pointed out by Hale (2000) regarding Wright's (1992)
reconstruction.


## 7. A Simple Argument.



Brueckner goes on in his 2003 to consider what he would later (2016)
call a modified version of *Simple Argument 1* or SA1:


* A. If I am a BIV, then my word
'tree' does not refer to trees.
* B. My word 'tree' refers to
trees.
* [?] C. I am not a BIV.



Brueckner (2016) suggests that premise B begs the question, since its
truth requires the existence of trees as referents for his word
'tree'. So to know that B is true, he would have to know
that he is "a non-BIV in a world containing trees, rather than a
BIV in a treeless vat world" (Brueckner 2016: 5).



To avoid this objection, Brueckner suggests the following modification
of SA1 (2003: 158, 2016: 5):


* A\*. If I am a BIV, then it is not the case
that if my word 'tree' refers, then it refers to
trees.
* B\*. If my word 'tree' refers,
then it refers to trees.
* [?] C. I am not a BIV.



Brueckner claims that B\* can be true even if there are no trees, so
that use of it here does not beg the question.



However, given widely held direct reference views of proper names,
indexicals, and natural kind terms, views that are strongly suggested
by the work of Kripke (1972), Kaplan (1977 [1989]), and Putnam (1975),
it is not obvious that the existential commitments of sentences
containing such terms can be removed by merely conditionalizing or
'hedging' the sentences. (For a useful discussion of
hedging see Yeakel 2016.)



'Tree' is a natural kind term. As such, it is plausible to
suppose that this term's primary semantic function is that of
predicating membership in the kind T to which all trees belong. But
suppose that there is no such kind T. In this case, the general term
'tree' would have no semantic value, since there simply
would be no such property as that of belonging to T. As a consequence,
Brueckner's premise B\* would express no proposition and would
have no truth value, since the term 'tree' would make no
semantic contribution to what is said by B\*. Thus, in order for
premise B\* to express a truth, there must be a natural kind T to which
all trees belong, and so Brueckner's claim that B\* can be true
even if there are no trees seems doubtful.



We should again note that use of premise (A\*) begs the question for
the same reason that was pointed out by Hale (2000) regarding
Wright's (1992) reconstruction.


## 8. Reconstructions Based on Self-Knowledge.



So far, all of the reconstructions of Putnam's anti-skeptical
argument that we have considered have involved, in various ways, the
use of disquotation. But one remaining type of reconstruction does not
involve the use of disquotation at all. (A major advantage, some might
say.) Rather, these arguments depend on the thesis that one can know
*a priori* that one's thoughts have a given content, even
when that content has an externalist semantics. Arguments of this sort
have the following form:


* (F)
 (p1)
I am thinking that P. (By privileged *a
priori* access to content.)
* (p2)
 
If I am a BIV, then I am not thinking that P. (By
Putnam's causal constraint.)
* [?] 
C 
 I am not a BIV.



Arguments of this form have been discussed and defended by Tymoczko
1989, Warfield 1998, and Brueckner 2003, 2005, 2016. I will rely on
Warfield's argument of form (F), which is:


* (W)
 (p1)
I think that water is wet.
* (p2)
 
No brain in a vat in an otherwise empty world can
think that water is wet.
* [?]  C 
 I am not a brain in a vat. (1998:
78)



(Warfield explains that an "otherwise empty world" is
"a world containing only the brain in a vat and whatever is
necessary to sustain the brain in a vat" (1998: 77).)



Warfield suggests that one major advantage of his argument (W) is that
it appears to avoid the charge of question-begging that (as
we've seen) is so often made against other forms of Putnamian
anti-skeptical argument. (A similar motivation is also suggested by
Brueckner 2016: 5.) This is because, Warfield says, he can justify a
claim to have *a priori* knowledge of both of the
argument's premises: premise 2 on the basis of externalist
thought experiments by Putnam and others; premise 1 by virtue of the
principle that one can always have *a priori* knowledge of the
contents of one's thoughts (pp. 78, 80).



By '*a priori* knowledge' Warfield means knowledge
that is obtained without either perceptual observation or empirical
investigation (1998: 80; see also McKinsey 1991). Warfield's
view then is that one can always have privileged *a priori*
knowledge of the propositional contents of one's thoughts (the
traditional principle of privileged access), even when these contents
are external or *wide*, in the sense that having a thought with
that content *logically implies* the existence of particular
objects or substances that are external to the agent (see the useful
entry by Gertler 2017 on
 self-knowledge).



Thus Warfield's attempt to defend the claim that he has *a
priori* knowledge of both premises of his anti-skeptical argument
commits him to a view that we will call *content
compatibilism*, the view that having privileged access to the
contents of one's thoughts is consistent with some of those
contents being externalist, or wide. Other proposals of anti-skeptical
arguments of the form (F), such as those by Tymoczko and Brueckner,
also commit their defenders to content compatibilism.



But content compatibilism is a controversial view. Some have
complained that it implies that we can have *a priori*
knowledge of far too many things (see McKinsey 1991 and 2002).
Consider for instance the case of Garrison, who thinks that Donald is
clueless, so that the following thought ascription is true:


* (G) Garrison thinks
that Donald is clueless.



On the direct reference view of names, (G) ascribes to Garrison a
thought that has as its wide content the singular proposition that
Donald is clueless. This content is wide in the sense that (with the
exception of Donald) anyone's having a thought with this content
logically implies the existence of things or substances that are
external to that person. In this case of course, the relevant external
object or substance is Donald.



Now given the principle of privileged access, Garrison can know *a
priori* that he thinks that Donald is clueless. But as we've
just seen, it is a logical consequence of Garrison's having this
thought that Donald exists. Hence, Garrison can merely *deduce*
that Donald exists from something he knows *a priori*, and thus
he can know *a priori* that Donald exists. But this consequence
is absurd. Surely no one can know that any given other person exists
without perceptual observation or empirical investigation. (A similar
argument can be given for thought contents expressed by use of
indexical pronouns and natural kind terms.)



I take this argument to be a *reductio* of content
compatibilism: one of these two principles, privileged access and
content externalism, must be false. One who endorses content
externalism should I think endorse a restricted form of privileged
access on which we can have privileged access only to the
*narrow* contents of our thoughts (see McKinsey 2002).



Given content externalism, then, Warfield cannot have the desired
*a priori* knowledge of premise 1 ("I think that water is
wet"). Does this mean that his use of premise 1 begs the
question? Apparently so. Certainly, from a Putnamian point of view,
the question is begged. For on that point of view, one could not have
warrant for premise 1 unless one had warrant to believe that (unlike a
BIV) one had satisfied the causal constraints on having the concept
water. Thus it would seem that--absent any *a priori*
knowledge of premise 1--one could not have warrant to believe
premise 1 unless one already had warrant to believe that one is a
non-BIV. (McLaughlin 2000 and Steup 2003 also contend that
Warfield's argument begs the question.)


## 9. A Successful Anti-Skeptical Argument?



It is doubtful whether Putnam's causal constraint alone can be
used to show, in a manner that does not beg the question, that any
arbitrary person is not a BIV. However, it is possible to show, using
Putnam's causal constraint, that the argument (SA) for
skepticism mentioned above that uses both the BIV scenario and the
closure principle (CP) is, in a sense*, self defeating*. Here,
recall, is (SA):


* (SA)  (1)
You know that the proposition that you have a
body entails that you are not a brain in a vat.
[Premise]
* [?] (2) 
If you know that you have a body, then you know that
you are not a brain in a vat. [By (1) and (CL)]
* (3)  But
you don't know that you are not a brain in a
vat. [Premise]
* [?] (4) 
You don't know that you have a body. [By
(2) and (3)]



In their arguments against skepticism, Putnam and his defenders have
been mainly concerned with providing arguments against premise (3) of
(SA). But in fact, Premise 1 of the skeptical argument itself may
provide the best reason for doubting Premise 3 of that argument. For
consider the following anti-skeptical argument (AS):


* (AS)  (1)
You know that the proposition that you have a
body entails that you are not a brain in a vat. [Premise (1) of
(SA)]
* [?] (2) 
You have the concept of a BIV. [By
(1)]
* (3)  But
no BIV has the concept of a BIV. [By the causal
constraint.]
* [?] (4) 
You are not a BIV. [By (2),
(3)]



(The inference from (1) to (2) here requires two additional, and I
hope obvious, assumptions: (1a) Knowing a proposition requires having
the concepts necessary for thinking the proposition, and (1b) The
concept of a BIV is one by which the known proposition is
grasped.)



Of course, the conclusion (4) of (AS) ("You are not a
BIV") does not imply that *you know* that you are not a
BIV. However, note that all of the other anti-skeptical arguments
considered so far also have this feature; they all have the conclusion
that the relevant agent is not a BIV. It is then inferred that the
agent *knows* that she is not a brain in a vat by virtue of her
having deduced the conclusion that she is not a BIV from premises that
she knows, always including assumed knowledge of the causal
constraint.



In this manner, any agent to whom the skeptical argument (SA) is
addressed may also reason through the argument (AS) to the conclusion
that she is *not* a BIV and then to the further conclusion that
she *knows* that she is not a BIV, and hence that premise (3)
of the skeptical argument is false. Thus in any such case, if the
relevant instance of premise (1) of (SA) is true, then the
corresponding instance of premise (3) will be false. Thus in any such
case, the skeptical argument will be shown to have at least one false
premise, and the argument (relative to the addressed person) will have
been refuted.



Note that there can be no issue of question-begging in an
anti-skeptical argument like this. First, it is not the person to whom
the skeptical argument is being addressed who is assuming premise (1)
of both (SA) and (AS). Rather, it is the *skeptic* who is
making that assumption. Second, the person being addressed can be
taken to be assuming premise (1) merely for the sake of
*conditional proof*. That is, she can be taken to be arguing
merely for the conclusion that *if* premise (1) is true then
premise (3) is false, so that at least one of argument (SA)'s
premises is false.



It would seem, then, that Putnam's causal constraint, if it is
in fact true, can be used to refute the skeptical argument that is
based on both the BIV scenario and the closure principle (CP).


## 10. Conclusion



We have looked at a number of attempts to reconstruct a Putnamian
anti-skeptical argument that uses Putnam's causal constraint to
refute the skeptical argument that is based on both the brain-in-a-vat
scenario and the closure principle (CP). Most of the anti-skeptical
arguments we looked at used the principle of disquotation in various
ways, and as a result, these arguments begged the question in similar
ways to Brueckner's original reconstruction of Putnam's
argument. Some of these arguments begged the question in a different
way, pointed out by Hale (2000).



We also looked at a class of anti-skeptical arguments that depend on
content compatibilism, the view that one can have *a priori*
knowledge of the contents of one's thoughts, even when those
contents are logically wide. I suggested an argument against content
compatibilism, the falsity of which opens this style of anti-skeptical
argument to the charge of question-begging.



Finally, we saw that Putnam's causal constraint, if true, does
in fact raise a serious problem for skeptical arguments of the form
(SA) that are based on both the BIV scenario and (CP). The problem is
that when the skeptical argument is applied to particular persons, the
causal constraint provides those persons with the grounds to show that
the skeptical argument when applied to them has at least one false
premise.