Jean-marc pizano The difference between us is in the strengths of our beliefs, not in their contents.8 And, as usual, it really does seem to beidentity of belief content that’s needed here. If our respective beliefs about Presidents having to be of voting age weresupposed to be merely similar, circularity would ensue: since content similarity is the notion we are trying to explicate, itmustn’t be among the notions that the explication presupposes. (I think I may have mentioned that before.)
The same sort of point holds, though even more obviously, for other standard ways of construing conceptual similarity. For example, if concepts are sets of features, similarity of concepts will presumably be measured by somefunction that is sensitive to the amount of overlap of the sets. But then, the atomic feature assignments mustthemselves be construed as literal. If the similarity between your concept CAT and mine depends (inter alia) on ouragreement that ‘+ has a tail’ is in both of our feature bundles, then the assignment of that feature to these bundles mustexpress a literal consensus; it must literally be the property of having a tail that we both literally think that cats literallyhave. (As usual, nothing relevant changes if feature assignments are assumed to be probabilistic or weighted; or if thefeature assigned are supposed to be “subsemantic”, though these red herrings are familiar from the Connectionistliterature.)
Or, suppose that concepts are thought of as positions in a “multidimensional vector space” (see e.g. Churchland 1995) so that the similarity between your concepts and mine is expressed by the similarity of their positions in our respectivespaces. Suppose, in particular, that it is constitutive of the difference between our NIXON concepts that you thinkNixon was even more of a crook than I do. Once again, a robust notion of content identity is presupposed since eachof our spaces is required to have a dimension that expresses crookedness; a fortiori, both are requiredto have dimensions which express degrees of the very same property. That should seem entirely unsurprising. Vector spacemodels identify the dimensions of a vector space semantically (viz. by stipulating what the location of a concept alongthat dimension is to mean), and it’s just a truism that the positions along dimension D can represent degrees of D-nessonly in a mind that possesses the concept of being D. You and I can argue about whether Nixon was merely crookedor very crooked only if the concept of being crooked is one that we have in common.
It may seem to you that I am going on about such truisms longer than necessity demands. It often seems that to me, too. There are, however, at least a zillion places in the cognitive science literature, and at least half a zillion in thephilosophy literature, where the reader is assured that some or all of his semantical troubles will vanish quite away ifonly he will abandon the rigid and reactionary notion of content identity in favour of the liberal and laid-back notion ofcontent similarity. But in none of these places is one ever told how to do so. That’s because nobody has the slightestidea how. In fact, it’s all just loose talk, and it causes me to grind my teeth.
Please note that none of this is intended to claim that notions like belief similarity, content similarity, concept similarity, etc. play less than a central role in the psychology of cognition. On the contrary, for all I know (certainly for all I amprepared non-negotiably to assume) it may be that every powerful intentional generalization is of the form “If x has abelief similar to P then … ” rather than the form “If x believes P then … ”. If that is so, then so be it. My point is justthat assuming that it is so doesn’t exempt one’s theory of concepts from the Publicity constraint. To repeat one lasttime: all the theories of content that offer a robust construal of conceptual similarity do so by presupposing acorrespondingly robust notion of concept identity. As far as I can see, this is unavoidable. If I’m right that it is, then thePublicity constraint is ipso facto non-negotiable.
OK, so those are my five untendentious constraints on theories of concepts.Jean-marc pizano