In this study I have argued on the basis of several examples that what we call our ‘I,’ what is most ‘own’ of ourselves, only exists by virtue of embracing the strangeness of our Körperlichkeit. This argument has major implications for our notion of identity. Identity, derived from the Latin identitas, means after all being literally the same. Normally it is said that ‘I’ is an expression of identity. ‘I’ am identical with ‘I,’ or ‘I = I.’ It is possible to change most parts of the körperliche dimension of our body and replace them by other matter. Therefore we need to ask whether the ‘I,’ which over time has had to identify repeatedly with other matter, is still the same or identical ‘I.’

The issue of identity is as old as Western philosophy. Plato recorded a famous statement by the pre-Socratic philosopher Heraclitus, who probably lived at the end of the sixth century BC: ‘Heraclitus says, you know, that all things move and nothing remains still, and he likens the universe to the current of a river, saying that you cannot step twice into the same stream’ (Cratylus: 402a). Because everything flows all the time – panta rhei – everything changes all the time, we cannot step into the same river twice. A river is never identical to itself because the water that flows in it is always other water. If we interpret Heraclitus's words in this way, we end up with quite a specific view of identity: something is only identical with itself when it consists of exactly the same parts at different moments.

According to this view, we can step into the same river twice if the river at moment t1 (river A) consists of exactly the same water as at moment t2 (river B): river A = river B only when all the water is the same in both cases. Because this is not the case, there can never be the same river. It is easy to see this when applied to our view of identity: there would be very few things which can be said to remain identical over the course of time. The composition of everything in nature is subject to change all the time, and this also applies to our bodies.