  For a Retentional model to amount to a viable form of PT-realism it must be possible for momentary states such as S to include change, succession and persistence in the forms in which we experience them. One difficulty here is the Retentional Simultaneity Problem noted in §3. The contents in any given Retentional specious present exist simultaneously – at least as measured by ordinary clock-time – but if they are to generate the appearance of succession they must avoid leaving the impression that the events they represent also occur simultaneously. If a number of tones are heard simultaneously, the result is obviously a chord rather than a succession. In fact, it is not just succession that the Retentional theorist needs to accommodate. Returning to Figure 14, it was stipulated that you see the pointer moving smoothly from half-past to quarter-to. Where is the movement in S? There may seem to be no real difficulty here: after all, we can easily call up a moving image in our memories or imaginations – as when we remember seeing a bird in flight, or a ball in motion – so we know that our minds are capable of generating dynamic imagery. There is, however, an important difference between the two cases. Running re-plays of past experiences in ordinary memory is a process which itself unfolds over time, but the dynamic re-plays required by the Retentionalist are supposed to occur at a single moment. Indeed, as processes which occur over time, remembered or imagined movements will themselves occur within momentary specious presents, and so their dynamic character will depend on that of retentions.