An introduction to the issue of mental state externalism…

How do our beliefs about the world come to have the contents they do? What makes my belief that water is wet a belief about the wetness of water? These questions are deep and difficult, and I shall certainly not attempt to answer them fully here. However, we can fruitfully treat one aspect of the problem, the issue of mental content externalism. Hopefully, this will be the start of a series of blogs (and responses!) in which we discuss externalism, and reach some substantive philosophical conclusions. But first I need to clearly set out the issues at stake.

In the introduction I raised the issue through the example of belief. But it is not only our beliefs that have contents in the relevant sense; rather, the issue attaches to all of the so-called ‘propositional attitudes’. A propositional attitude is what it says on the tin: an attitude to a proposition. I believe that the Holy Spirit doesn’t exist, hope that I won’t go to Hell, desire that I will go to Heaven, and so on. In each example, the embedded sentence after the ‘that’ clause expresses a proposition, and the verb before the ‘that’ clause expresses an attitude towards that proposition – in my examples, the attitudes are belief, hope and desire. We call the embedded proposition the ‘content’ of the propositional attitude; what is at stake in the present debate is how this content is determined. At the present stage, we do not need to commit to a detailed answer to the question of what contents are. What we do need to acknowledge is the basic thesis that contents are comprised out of elements called notions or concepts, whose nature and arrangement determines the nature of the content as a whole. I trust that this will not be too controversial: after all, it seems, intuitively, that the contents ‘water is wet’, ‘water is potable’, and ‘Coca Cola is potable’ share certain things in common, and that what is shared is the occurrence of the same conceptual elements. Once again, we do not need to make any substantive metaphysical commitments about what concepts are. Finally, we should note the following criterion of individuation for mental states: if two mental states have different contents, then they are different mental states.

We’ve seen the distinction between attitude and content, and that contents are composed out of elements called concepts. To understand mental state externalism, we need to introduce one more philosophical concept: supervenience. This may be defined as follows: a set of properties A supervenes on a set of properties B if and only if any two individuals x and y which share all properties in B must also share all properties in A. The concept of supervenience was introduced into philosophy by G. E. Moore in the context of ethics and aesthetics. One supervenience claim is that the beauty of a painting supervenes on the arrangement of paint on the canvas: crudely, the beauty of the painting remains constant so long as you don’t muck about with the paint. A different supervenience claim is at stake between internalists and externalists. The internalist thinks that the contents of a subject’s propositional attitudes supervene on the subject’s internal states; the externalist denies this claim. What counts as a subject’s ‘internal states’? To keep things simple, assume that materialism is true: that is, that everything that exists is physical or material. My internal states are therefore wholly constituted, or determined by, the physical particles which make up my body. Thus, two subjects made up of the same particles in the same arrangement are in the same internal state. Now we can express the internalist’s thesis as follows: two physically identical subjects necessarily have mental states with the same contents. The externalist thinks that two internally identical subjects could be in different mental states, because their propositional attitudes could have different contents. Note that internalism and externalism are types of position, rather then concrete, particular positions: internalists can disagree about which internal states mental contents supervene on; externalists can disagree about which external factors play a role in determing the contents of a subject’s propositional attitudes.

In my next post, I’ll consider arguments for the the externalist’s thesis that two internally identical subjects could be in different mental states. This man looms large…