Henrich's Distinction Between Identity and Numerical Identification ()
Henrich distinguishes philosophical from social-psychological concepts of identity. In the philosophical concept, you have identity as soon as you have a single thing. For example, there is a person. You can identify it as a person. Therefore, it has a philosophical identity -- what Habermas is soon (p. 102.1.5) calling "numerical" identification. You don’t need additional knowledge about its unique characteristics to say that it has philosophical identity. You wouldn’t say it has "a" philosophical identity; it just has philosophical identity. It is identifiable as a person. It doesn’t acquire or lose this sort of identity if, say, it goes through some changes while still remaining a person.
In the social psychological sense, by contrast, people can acquire unique identities, but they don’t necessarily do so. Acquiring an identity makes you independent. With an individual identity, you can avoid the influence of others; you can be autonomous -- although the concept of autonomy may entail no more than being "a speaking and acting subject in general" (p. 102.1.6). This is your social psychological identity. If multiple individuals have the same kind of social psychological independence, then you can say they have philosophical identity as autonomous individuals, and again (on the philosophical level) you can say they are indistinguishable for philosophical purposes.
Notwithstanding Henrich's distinction between philosophy and social psychology, this really sounds like nothing more than a distinction between levels of analysis. If you're philosophizing on a grand scale, you are apt to talk about autonomous individuals, but not about any particular autonomous individual (except perhaps using a hypothetical one to illustrate a point). If, on the other hand, you are philosophizing on the micro level, you notice distinctions between individuals. It seems simplistic to say that you "acquire" identity (). More likely, people acquire various levels of independence, and you would notice the distinctions among their levels of independence if you were looking at it on the micro level.