  The Simultaneity Problem (in its Retentional guise) may not in principle be insuperable, but in addition to establishing the bare possibility of objectively simultaneous contents appearing successive, Retentionalists should also aim to supply an intelligible and credible account of how this appearance is created. Retentional theorists subscribe to the doctrine of PT-realism, and so believe that change, succession and persistence figure in our immediate experience. We saw in §3 that some realists also subscribe to the Immediacy Thesis, and hold that change, and other dynamic properties, feature as vividly in our experience as colour or shape. For deep-seated structural reasons, Retentional models have difficulty in accommodating the Immediacy Thesis. If retentions have the same force and vivacity as ordinary (presently occurring, first-order) experience, as they do on the Non-Modal variant, there is the risk of flooding consciousness with enormous quantities of surplus content – content which we have no reason to suppose exists, as we saw in §6.2. It is thus not surprising to find that Retentional theorists generally subscribe to the Modal form of the doctrine, and hold that retentions lack the force and vivacity of presently occurring contents. But this option also brings a danger: if retentions are too unlike ordinary experience, there is a risk they will prove incapable of doing the job they are intended to do: namely, be the purveyors of our immediate impressional experience of persistence, succession and change. To maintain that the dilemma is fatal to the prospects of the Retentional approach would be premature. But Brentano and Husserl’s shifting position on the nature of retentions – recall the appeals to unreal objects, judgements, primitive phenomenal features, additional dimensions, temporal modes of presentation and the like – is indicative of the difficulty of finding the right balance here, or so might purveyors of alternative forms of realism allege.