Let me first get rid of the ‘for at least some thoughts’ qualifier. If externalism is true about the meaning of ‘at least some thoughts,’ it probably needs to be true for all thoughts. In order for this not to be the case, one would have come up with criteria delimiting contents that could be known simply by reflecting upon them from those which could be known only through consultation with the environment. For reasons that I won’t get into now, I find this to be unlikely.
Back to the main argument: the problem with semantic externalism is that, if true, one cannot tell for sure what one is thinking without consulting the environment. Am I thinking about water or twater? Well, it depends on the world in which I happen to be. I may believe that I am thinking about water, only subsequently to discover that I’m actually on Twin Earth and therefore that I’m really thinking about twater. Such would be the case for all of my own beliefs about what I am thinking. Without some sort of empirical investigation into the world that I am thinking about, I might not know what I am thinking at all. That’s weird.
In my previous post I said that I would apply McDowell’s argument for the intrinsic intentionality of mental states to the issue of incompatibilism. Here goes. When it comes to knowing what I mean, there surely are more options than these:
(a) I know directly and apriori the meaning of my thought.
(b) I can discover the meaning of my thought only through empirical investigation, by discovering the relevant features of my environment that function as the meaning-relevant truth-conditions of that thought.
Much of the dispute between compatibilism and incompatibilism assumes that these are the two options. This is greatly restrictive.
Consider that I am thinking about the square root of two. A cursory familiarity with number theory let’s me know that I really have no firm understanding what I mean when I think the square root of two. That rules out (a). But for definitional reasons, there is no empirical field to be had where I could venture out to ‘discover’ what the world holds in regard to this thought. This rules out (b). I rather have to think through my thought. And this is not just the case with strange thoughts like the square root of two. For in fact, I would say that we very rarely are completely clear on just what it is that we are thinking or meaning. For further proof, just consider this question: are you happy?
This then is the problem with the dispute over incompatibilism: it is the assumption that ‘reflection’ or ‘introspection’ is a sort of looking inward in just the same way that seeing is a ‘looking outward.’ But this is a bad analogy. And this is McDowell’s point: if thoughts are intrinsically intentional, that means that they are intrinsically ‘deep.’ This is a metaphorical way of putting his insight that the ‘contents’ of our thoughts are not something that, once clear on, we have the further burden of comparing to the world; for the content of our thinking just is the world. I think that this is clear once we disabuse ourselves of our Cartesian prejudices.