Transcendental arguments aim to overcome the sceptic by showing that in order for the sceptical challenge to be made, it must be false. The sceptical challenge is illegitimate in that, in order to make her sceptical challenge, the sceptic relies on the truth of the belief she is attempting to show to be unjustified.

A transcendental argument refutes the sceptic indirectly, by undercutting her position. The use of transcendental arguments was first proposed by Kant.

Þ Either the sceptical challenge is false or it is meaningless nonsense.
[So the sceptical challenge can’t be true! so the sceptic is defeated…]

Putnam’s brains in vats
What if I’m a brain in a vat? Perhaps what I think is the external world is just an illusion.

In a possible world in which I am not a BIV, my English words refer to real objects e.g. vats, so “vat” refers to a real vat object external to me.
In a non-BIV world, I can meaningfully say “I am a brain in a vat”, but of course this is false.

In a possible world in which I am a BIV, my words don’t refer correctly – my language doesn’t function as I think it does – in vat-English, “vat” doesn’t refer to a real vat, but to electric impulses (or whatever).

\ In a BIV world, I cannot say meaningfully “I am a brain in a vat” because my language doesn’t make proper sense.

\ either it is the case that I am not a brain in a vat OR my language doesn’t function as I think it does (which means that I cannot coherently hypothesise that I am a brain in a vat)
i.e. either the sceptical challenge is false or it is meaningless nonsense (in any case, “I am a brain in a vat” is never true! sceptic defeated.)

In order to question whether the external world is real, the sceptic relies on the truth of the belief she is attempting to show to be unjustified i.e. she has to implicitly assume that the external world is real in order to make the sceptical challenge.

[The questionable point in this argument is whether our language, in terms of reference and meanings, really functions in the way Putnam claims.]


Kripke’s Wittgenstein’s private language argument (c.f. private language text)
What if solipsism is true? Perhaps there is no external world.

Wittgenstein argues that in order for my language to function effectively, in order for me to use it consistently, there must be external checks that I can make to ensure that I am doing so i.e. there must be a community of other language-users or at least aspects of an external world against which I can check my usage to ensure I am being consistent in the usage and meanings of my words.

He targets the idea of a private language (a language to refer to my own private sensations, so that another person cannot understand the language; the idea that I know what I mean, and that other people cannot know exactly what I mean because I have privileged direct access to my own meanings of my words and I determine the meanings of my words myself; subjective experience is part of the meanings of my words) and argues that such a language cannot exist because we would have no way of ensuring we were using that language consistently (c.f. examples of the diarist §258, and train timetable §265). Rather, we need some external check to ensure we are using our words consistently and to amend and correct our usage. There is no “inner” component of meaning; the meaning of the words is how they are used publicly (the beetles cancel out §293).

\ either it is the case that an external world (probably including other language-users) exists OR I have no means of ensuring that I am using my language consistently, in which case I don’t know what I am talking about (which means that I cannot coherently hypothesise that there is no external world)
i.e. either the sceptical challenge is false or it is meaningless nonsense (in any case, “There is no real external world” is never true! sceptic defeated.)

In order to question whether the external world is real, the sceptic relies on the truth of the belief she is attempting to show to be unjustified i.e. she has to implicitly assume that the external world is real in order to make the sceptical challenge.


BUT
What if I’m talking nonsense? What if my present usage of words doesn’t agree with my past usage? Perhaps I am not presently conforming to my previous linguistic intentions? Perhaps I am doing the same thing, not using my language consistently, not following the same rules?

But if these questions are meaningful, then I’m not talking nonsense [so either the sceptical challenge is false or I cannot express such a challenge coherently because I have no way to ascertain what my words mean – the sceptical challenge is either false or it is meaningless nonsense i.e. never true! sceptic still defeated.]

In order to question whether her words make sense, the sceptic relies on the truth of the belief she is attempting to show to be unjustified i.e. she has to implicitly assume that her words do make sense in order to make the sceptical challenge.


Descartes would presumably dismiss the hypothesis that I don’t know what I am talking about in a similar way to how he dismisses the hypothesis that his senses might be constantly deceiving him in Meditation I: only nutters, like the man who thinks he has an earthenware head, could proceed on this basis.

Note also though, that maybe Descartes could have used an argument like this interpretation of Wittgenstein (but doesn’t) to demonstrate the existence of the external world. This might be more fruitful than Descartes’s own attempts in Meditation VI; he maybe could demonstrate the existence of the external world without recourse to God. You might also want to consider the extent to which this transcendental argument is a priori….

[The questionable point in the argument is whether external checks really are necessary for us to know we are using our language, or following a rule, consistently. Maybe you think a private language is possible, in which case the transcendental argument won’t run.]


A version of Descartes’s cogito
What if I don’t exist? Perhaps I don’t exist.

In order for me to say “Perhaps I don’t exist”, I must exist!

\ either it is the case that I exist OR there is no way that the sceptical challenge could be made
i.e. either the sceptical challenge is false or it is meaningless nonsense (in any case, “I don’t exist” is never true! sceptic defeated.)

In order to question whether she exists, the sceptic relies on the truth of the belief she is attempting to show to be unjustified i.e. she has to implicitly assume that she exists in order to make the sceptical challenge.


Of course, the main problem with the cogito is still that it doesn’t prove very much. It doesn’t yield any information as to what type of thing I am, whether I am a unified thing, or disparate, a thing that lasts for a period of time, physical, non-physical etc. It succeeds in concluding that something exists (which Descartes might be happy with as a starting point), but this doesn’t tell us very much.