Repetition changes nothing in the object repeated, but does change something in the mind which contemplates it. Hume’s famous thesis takes us to the heart of a problem: since it implies, in principle, a perfect independence on the part of each presentation, how can repetition change something in the case of the repeated element? The rule of discontinuity or instantaneity in repetition tells us that one instance does not appear unless the other has disappeared– hence the status of matter as mens momentanea. However, given that repetition disappears even as it occurs, how can we say ‘the second’, ‘the third’ and ‘it is the same’? It has no in-itself. On the other hand, it does not change something in the mind which contemplates it. This is the essence of the modification. Hume takes as an example the repetition of the cases of the type AB, AB, AB, A… . Each case of objective sequence AB is independent of the others. The repetition (although we cannot yet properly speak of repetition) changes nothing in the object or the state of affairs AB. On the other hand, a change is produced in the mind which contemplates: a difference, something new in the mind. Whenever A appears, I expect the appearance of B.- Deleuze, "Difference and Repetition"