Maybe everybody is right here? Basically the examples treated in this thread are ones where both imperfect and aorist would be correct, and whatever difference there was in these examples, it is a slight one of nuance. When the poet makes a choice with what form to use, all of these aspects (shade of meaning, formulas available to him, euphony) influence him (unconciously of course).
Early this year I read a whole book that more or less concentrated on this question (Maria Napoli: Aspect and Actionality in Homeric Greek). I have of course forgotten most of by now (
) but if you have an unhealthy interest in this stuff like I have, you might want to have a look at it too… The main point I think is that the imperfect (or the present stem in general) is used for an undelimited action, and the aorist for a punctual action (the book used of course a much more refined and nuanced linguistic vocabulary). With transitive verbs, it’s often pretty straightforward to translate in English:
I shot him (dead). AORIST
I shot at him. IMPERFECT
With intransitive verbs (i.e. verbs that don’t have an object), translation is often a bit more difficult. A very tentative translation for the beginning of Book 8 of Odyssey:
When Dawn appeared,
Alkinoos got [leisurely] out of bed,
and Odysseus sprang up too.
But if there really is a difference in meaning, it’s definitely nothing as strong as this. Alkinoos is at home in his own kingdom, he can take all his time to get up, while Odysseus is insecure amid the Phaeacians and has yet to show them what he’s worth, hence a more prompt getting up from bed.
Let me quote also Chantraine’s “explanation”, which I don’t understand, so I don’t attempt to translate it. (But note passé simple in jeta, imparfait in faisait)
"A côte de l’aoriste, l’imparfait indique un procès qui se déroule auprès de celui qu’exprime l’aoriste: A 3-4 πολλὰς δ᾽ ἰφθίμους ψυχὰς Ἄϊδι προΐαψεν / ἡρώων, αὐτοὺς δὲ ἑλώρια τεῦχε κύνεσσιν “elle jeta en pâture tant d’âmes fières de héros, tandis que ces héros mêmes elle faisait la proie des chiens…” Other examples given are Od 8.532, Od 8.63
(Grammaire Homérique t. 2, p. 193)
There seems to be two other instances of aorist ὦρτο for getting up from bed: Od 14.499 (clearly means “sprang up” and Od 23.348 (not so obvious, but a quick waking up seems preferable to me, because the hasty runover lines suggest some immediacy there).