What I think (but my English ought to be far better... so, in telegraphic style):<br /><br />- [face=SPIonic]lu=sai[/face] : perfective aspect. Action considered as a single point, you speak of it only to put it on a chain of actions, as a single link of the chain. You don't draw attention to the details nor to the development of the action. It can also mean "free (in a particular case)" or "free (straightaway)". All three notions (single point, particular case, straighaway) are connected.<br /><br />- [face=SPIonic]de/xesqai[/face] : imperfective aspect. The author reminds you of the different phases in the development of the action, evolutions, efforts needed... The action is considered as interesting in itself. Present (infinitive) is also used to speak of recurring actions or actions that can begin at an undefinite point in time (now or later... no matter)<br /><br />For example (imperative):<br />[face=SPIonic]le/ge[/face] (present imperative) : "say", "speak" (when you are ready... you can begin and stop and begin again... we will hear your voice for some time... you will say a lot of things...)<br /><br />as opposed to <br />[face=SPIonic]ei)pe/[/face] (aorist imperative) "Tell me" (sthraightaway, about this particular thing...)<br /><br />Another example (infinitive):<br />[face=SPIonic]Xalepo\n to\ poiei=n, to\ de\ keleu=sai r(a/|dion[/face] "It is difficult to achieve (present) while it is easy to command (aorist)."<br /><br />By means of the present [face=SPIonic]poiein[/face] we are reminded of all things needed by an achievement (reflection, decisions, determination, skills, efforts...), while the aorist <br />[face=SPIonic]keleu=sai[/face] denotes the straightforwardness of such an action ("Study the whole dictionary by heart. On with it !")<br /><br />This is my "personal" view of the opposition between present and aorist. I was not yet able to make it public until now. So thanks to you all.