The Philebus has lots of interesting things to say about the psychology of desire.
The desire involved when a person is thirsty, for example, involves the memory of the state of not being thirsty which supplies the drive and impulse towards finding something to drink. Presumably, the drive to find a drink to remove a thirst involves the conjuring from memory of some appropriate representation of the proper object of desire or perhaps of the proper state of that desire being fulfilled. Socrates then goes on to distinguish two cases involving a person who is in pain but can remember the pleasant things he lacks. In the first, he has a ‘clear hope’ (elpis phanera 36a8) of attaining what he lacks. In that case, the memory provides some pleasure while he is also experiencing pain (36a–b). In the second, he is both in pain and also aware that there is no hope of replenishment. In that case his suffering is two-fold (36b–c). We should note, then, that hopes and desires all involve some activity of memory since it is memory which provides the store of experiences which can be drawn upon to generate the appropriate objects of pursuit in any given situation and which allows the animal to bring to mind some state (which it has experienced in the past) which is the opposite of its present condition.
My question is: what is the force of the qualification phanera at 36a8? It seems to me that there are two possibilities. First, what we might call an ‘internalist’ view, is that it shows that to the hoper, as it were, the hope is clear and vivid. That clear and vivid character of the hope is what allows it to be a source of pleasure even though the hoper is also in pain. And the clear and vivid character of the hope is irrespective of whether in actual fact what is being hoped-for is likely to be attained. For all that it matters here, it could be a very vivid and arresting sort of hope that is extremely unlikely to come to fruition.
Second, what we might call an ‘externalist’ view, is that the hope is phanera just in case that the object that is being hoped-for is indeed likely to be obtained. (This may be in addition to the hoper being convinced that it is likely to be obtained or it may not; presumably, good hopers tend to hope for things that are likely to be obtained.)
(The same might be said of despair, of course: I might have a ‘clear’ desperation both in cases where I merely think that what I need is unlikely to come my way although in fact it is not at all unlikely, and also in cases where I accurately recognise the unlikelihood of my getting what I need.)
All in all, I’m not sure I can see much in the text at 36a that points one way rather than the other for certain. And perhaps that’s not a surprise. After all, it is in the next four pages or so that Socrates turns to outline to Protarchus that there is a very important distinction to be made between the pleasures to be had from hoping that are true and those that are false, although they may both seem pleasant enough to the hoper.