Abstract
According to a second hypothesis, the Rrelation that makes two private concepts (the mental files of two distinct individuals) instances of the same shared concept is simply the fact that the two files refer to the same thing. This "referentialist" hypothesis, which we have rejected as a principle for individualizing private concepts, turns out to be much more acceptable if applied to shared concepts. According to this hypothesis, for two distinct subjects to be said to share a concept, it is sufficient for each of these subjects to possess a concept (a mental file) of some kind relating to the same thing as that of the other. Or to be more precise: this is sufficient in normalcases .
Normal cases are those in which what I call the Strawsonian norm is respected. The Strawsonian norm demands that there be a one-to-one correspondence between the entities in the environment that the subject represents to himself, and the mental files by means of which he represents them. It implies that, whatever the entity represented, a rational subject must represent this entity through one and only one mental file. When the Strawsonian norm is not respected by one of the candidate subjects for conceptual sharing, the fact that the mental files involved are co-referential isno longer sufficient to guarantee sharing. An additional condition must then be met: the content of the concepts must be sufficiently similar in both cases.
The Strawsonian standard, however, is not universally accepted. There is a rival view, which I myself have defended in the past, according to which, when a subject realizes that two mental files co-refere, he must not merge the two files but "link" them so that information can flow freely between them. The existence of a plurality of co-referential folders is not necessarily an error, according to this rival conception, but may simply reflect the fact that the single object to which the folders in question refer appears to us from distinct perspectives that are equally legitimate. Indexical concepts incorporate such contextually shifting perspectives. The corresponding mental files, because they are based on a certain contextual relationship to the object, are temporary files that are available for thinking about an object only as long as we are in that relationship with it. When the relationship changes (when the context changes) we have to resort to another mental file to continue thinking about the object.
But, as many authors have pointed out, the change of perspective on the object that results in the replacement of one indexical expression ("today") by another ("yesterday") no more affects the stability of the underlying concept than does the change of conception. Contrary to what I argued earlier, the indexical perspective does not play a part in the individualization of the concept, identified with the thin file. It belongs to the thick file, just like conception. Yet what the Strawsonian norm rightly proscribes is the simultaneous existence of a plurality of thin folders referring to the same object.
