  Many realists have no doubt found the Retentional approach appealing because it offers a simple and intuitively satisfying explanation of how an experience of succession differs from a mere succession of experiences: in the former case, the contents forming the succession are presented together, as an ensemble, to a single momentary awareness. Brentano and Husserl both subscribed to The Principle of Simultaneous Awareness (PSA) ‘No succession of awarenesses – no matter how close together in time they come – can, by itself, account for an awareness of succession; it must be the case that an awareness of succession derives from simultaneous features of the structure of that awareness’ (Miller (1984: 109). As we saw in §5.5, Meinong and Husserl both argued – correctly – that the successive phases of a temporally extended awareness of the sort advocated by Stern needed to be unified, and both realized that a unifying act which is not temporally extended does not face the same difficulty. Indeed, it may well be that some theorists, consciously or unconsciously, have found the Retentional approach appealing because of the way it (in effect) reduces the problem of diachronic phenomenal unity to the comparatively straightforward problem of synchronic unity. Although the latter is by no means unproblematic – there are different accounts of it – it is at least widely accepted that there is such a thing as synchronic phenomenal unity.