Objections To Putnam's Argument That We Have Handless

Scepticism about knowledge has been a problem in epistemology for centuries. One sceptical scenario holds that a person cannot actually know any ordinary piece of knowledge, such as the fact that they have hands. This is because it is possible that they are actually a handless brain in a vat being made to perceive an external world, when in fact they are only seeing computer images. Hilary Putnam argues that such sceptical scenarios are not actually problematic because the language used by handless brains in vats and real people refer to different things. However, Putnam’s success in regards to solving sceptical scenarios has been questioned by other philosophers.
Putnam argues that we can know that we are not brains in vats because, if we
The most reasonable of these objections is the notion that Putnam’s argument could be equally well proposed by a person who is actually a handless brain in a vat. This is clearly problematic, as it would mean that Putnam’s argument does not succeed in confirming that we are not handless brains in vats. For example, when an individual, who is actually a handless brain in a vat, says the sentence ‘I am not a handless brain in a vat’ they may conclude (after following Putnam’s argument) that they are not in fact a handless brain in a vat because they can express the proposition that they are not. Further, an individual in vat-world would not know that, when they say ‘I am not a handless brain in a vat’, their sentence actually refers to non-external properties. To them, when they say ‘I am not a handless brain in a vat’, it would seem as if their proposition expresses that fact in the external sense of the words. This means that, because they could conclude that they are not a handless brain in a vat when in fact they are, this person may actually be a handless brain in a vat and not know it (which of course does not solve scepticism) (Tymoczko 1989, pp. 268-287). This still means that we could be handless brains vats and reach the conclusion that we are not. Therefore, we do not know that we are not handless brains
Suppose that a person had, up until recently, lived a regular life in the external world before they became a brain in a vat. In this scenario, it is plausible that the language used by this person in vat-world may not be used to refer to different things than that which they used in the external world. This person would (incorrectly) use non-vat English to refer to what they would still believe to be external trees, but would actually be image trees (Tymoczko 1989, p. 294). In this scenario Putnam’s argument would not even succeed in confirming that individual’s in vat-world refer to different things than they do in the external world. This is because a recently envatted individual would still be using the same words, which refer to external properties, in a world where there are no external properties. This means that such a person could say the proposition ‘I am not a handless brain in a vat’, believe it to be true, and express it using the external sense of the proposition, and consequently conclude that their proposition was true. However, this would be incorrect because they would actually be a handless brain in a