I show that some of the most initially attractive routes of refuting epistemological solipsism face serious obstacles. I also argue that for creatures like ourselves, solipsism is a genuine form of external world skepticism. I suggest that together these claims suggest the following morals: No proposed solution to external world skepticism can succeed which does not also solve the problem of epistemological solipsism. And, more tentatively: In assessing proposed solutions to external world skepticism, epistemologists should explicitly consider whether those solutions (...) extend to knowledge of other minds. Finally, and also tentatively: epistemological solipsism warrants more philosophical attention than it currently enjoys. (shrink)

Putnam’s vat argument is intended to show that I am not a permanently envatted brain. The argument holds promise as a response to vat scepticism, which depends on the claim that I do not know that I am not a permanently envatted brain. However, there is a widespread idea that the vat argument cannot fulfil this promise, because to employ the argument as a response to vat scepticism I would have to make assumptions about the content of the premises and/or (...) conclusion of the argument that beg the question against the sceptic. In this paper, I show that this idea is mistaken. (shrink)

If it works, I can use Putnam’s vat argument to show that I have not always been a brain-in-a-vat. It is widely thought that the vat argument is of no use against closure scepticism – that is, scepticism motivated by arguments that appeal to a closure principle. This is because, even if I can use the vat argument to show that I have not always been a BIV, I cannot use it to show that I was not recently envatted, and (...) it is thought that the claim that I am not justified in thinking that I was not recently envatted is all that the closure sceptic requires. In this paper I first argue that scenarios in which I have been recently envatted are inadequate for the sceptic’s purposes, and so the standard argument that the vat argument is of no use against closure scepticism fails. I then argue that it is not possible to revise the standard argument to meet my objection. I conclude that, if it works, I can use the vat argument as a defence against closure scepticism. (shrink)

This article surveys recent literature by Parsons, McGee, Shapiro and others on the significance of categoricity arguments in the philosophy of mathematics. After discussing whether categoricity arguments are sufficient to secure reference to mathematical structures up to isomorphism, we assess what exactly is achieved by recent ‘internal’ renditions of the famous categoricity arguments for arithmetic and set theory.

Hilary Putnam’s BIV argument first occurred to him when ‘thinking about a theorem in modern logic, the “Skolem–Löwenheim Theorem”’ (Putnam 1981: 7). One of my aims in this paper is to explore the connection between the argument and the Theorem. But I also want to draw some further connections. In particular, I think that Putnam’s BIV argument provides us with an impressively versatile template for dealing with sceptical challenges. Indeed, this template allows us to unify some of Putnam’s most enduring (...) contributions to the realism/antirealism debate: his discussions of brains-in-vats, of Skolem’s Paradox, and of permutations. In all three cases, we have an argument which does not merely defeat the sceptic; it also shows us that we must reject some prima facie plausible philosophical picture. (shrink)

Philosophers tend to presuppose a close relationship between language and thought. They express and defend this conviction in different ways. I shall focus on the relation between the thinkable and the expressible, as stated in the Inexpressibility Thesis.

For several decades, Carnap's philosophy of mathematics used to be either dismissed or ignored. It was perceived as a form of linguistic conventionalism and thus taken to rely on the bankrupt notion of truth by convention. However, recent scholarship has revealed a more subtle picture. It has been forcefully argued that Carnap is not a linguistic conventionalist in any straightforward sense, and that supposedly decisive objections against his position target a straw man. This raises two questions. First, how exactly should (...) we characterise Carnap's actual philosophy of mathematics? Secondly, is his position an attractive alternative to established views? I will tackle these issues by looking at Carnap's response to the incompleteness theorems. Drawing on arguments put forward by Gödel and Beth, I show that some crucial aspects of Carnap's positive account have remained underdeveloped. Suggestions on what a full evaluation of Carnap's position requires are made. (shrink)

The argument that has inspired much of the recent discussion of the logical relationship between these views is found in Putnam : If externalism is true, then if S were a brain in a vat, S’s utterances of the sentence “I am a brain in a vat” would not express the proposition that S is a brain in a vat. S’s use of the words “brain” and “vat” would not refer to a real brain or vat, just as, in a (...) Twin Earth-style thought experiment, the Twin Earthling cannot refer to water with his use of the term “water.” If we accept that generally we have knowledge of the contents of our utterances, then, if S knows that her utterances of “brain” and “vat” mean brain and vat, it will be possible for S to know that she is not a brain in a vat. For if S has authority with respect to the contents of her utterances, then she can know that her utterance, “I am not a brain in a vat,” refers to brains and vats. On externalism, since S would not refer to brains and vats if she were a brain in a vat, she could know by mere introspection that she is not a brain in a vat. In fact, S can come to know many arbitrary propositions about the external world simply by attending to the contents of her thoughts. For if externalism is true, she can argue, then certain empirical conditions must be satisfied if she is even to have the thoughts about the external world that she does; since she knows what she is thinking, she knows these empirical conditions are satisfied. Thus, if S knows that she is thinking about brains and vats, then she can know that she is not a brain in a vat ; for if she was a BIV, then she would not be thinking about brains and vats, but instead about electrical impulses or some such thing. The standard BIV argument against scepticism, therefore, cannot be correct. This line of argument can then be used to conclude more generally that scepticism is false; for the argument can be run with virtually any utterance or thought with empirical content. If S knows that she is thinking about trees, for example, then she can know that there are trees. (shrink)

Hilary Putnam (1981) proposed an interesting and much discussed attempt to refute a skeptical argument that is based on one form of the brain-in-a-vat scenario. In turn, Putnam’s attempted refutation is based on content externalism (also known as semantic externalism). On this view, the referents and meanings of various types of singular and general terms, as well as the propositions expressed by sentences containing such terms, are determined by aspects of the speaker’s external environment. In this entry, we will consider (...) the basic features of and problems with Putnam’s original argument, and we will also present and discuss several of the most important attempts to reconstruct or improve upon that argument. (shrink)