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  • Content Externalism and Brute Logical Error
  • John M. Collins (bio)

I. Introduction

Externalism with respect to content is the thesis that the contents of an individual’s mental states are fixed, not just by the intrinsic physical characteristics of the individual, but also in part by the external circumstances of the individual. This idea can be illustrated by means of thought experiments involving pairs of ‘twins’ who are identical with respect to their intrinsic features yet who differ mentally because of differences in their environments. The thoughts of a thirsty earthling may turn to water. Suppose that an earthling has a molecule-for-molecule twin on a very distant planet, a planet identical to Earth except that wherever Earth has H2O, Twin Earth has XYZ, which is superficially indistinguishable from water. When the twin is thirsty, her thoughts will turn instead to twater, as we may call it. Externalism about content is a metaphysical thesis, but it has epistemological implications. Many have argued that externalism is incompatible with a suitably rigorous thesis about the authoritative, introspective1 self-knowledge we seem [End Page 549] to have with respect to our own thought contents. The earth individual’s introspective evidence underdetermines the thought content; if she were thinking a twater thought, her introspective experience would be just the same2.

Externalists have argued in various ways that externalism and authoritative self-knowledge are compatible. Some opt for a reliabilist strategy; since whatever determines that a thought employs the concept water instead of the concept twater will also determine that the second-order thought I am thinking that water is dripping involves the concept water as well. The second-order thought is guaranteed to be correct, and thus is a knowledgeable self-attribution. (John Heil, 1988, is a notable example of this strategy.) Other compatibilists maintain that arguments for the incompatibility of externalism and authoritative selfknowledge depend on a conflation of knowledge of content simpliciter with discriminative or comparative knowledge of content (knowledge of sameness or difference of content). Lois Lane knows who the man of steel is, and she knows who the mild-mannered reporter is; she just does not know that they are one and the same. Some argue that it is the same with introspective knowledge. One can know that one is thinking about water without being able to discriminate this thought introspectively from all other thoughts that play a similar psychological role. (Falvey and Owens, 1994, takes this tack.)

Some of those who defend the compatibility of externalism and authoritative self-knowledge take themselves to be defending the externalist thesis itself. Kevin Falvey and Joseph Owens say:

[I]f this line of thought [the incompatibility of externalism and authoritative selfknowledge] is correct, then externalism is in serious trouble, for while philosophers in the Cartesian tradition have tended to exaggerate the certainty and scope of self-knowledge, it is difficult to deny the intuition that one’s knowledge of one’s own occurrent propositional mental states is frequently direct and authoritative… Any philosophy of mind that cannot accommodate and explain these intuitions must be mistaken.

(Falvey and Owens 1994, 108) [End Page 550]

Most externalists do not, however, believe that the plausibility of externalism depends on its being compatible with authoritative discriminative self-knowledge of content.

DASK: For any subject S and any of S’s mental state tokens M1 and M2, S can determine through introspection whether M1 and M2 have the same, or different, contents.

Content externalism looks to be incompatible with DASK. Were one to be transported, unawares, to Twin Earth, where one encountered twater and developed the capacity to think about twater, one would have no way of telling by introspection that one is using a concept different from the old water concept. Here, difference of content is not transparent to the subject. Similarly, one could encounter tomatoes in two very different situations (Campbell’s tomato soup, say, and tomatoes eaten right from the vine, but pronounced ‘to-mah-toes’), and think tomatoes (to-may-toes) are tasty and tomatoes (to-mah-toes) are tasty, while supposing that these are two distinct thought contents, about two different kinds of food. Sameness of content is not...

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