OK, Del, you're gonna hate me for this one, but I had to do it, not to argument my tire iron theory, but because too many times I see these two literary forms mixed up in people's arguments. The italicized parts are from Wikipedia, my own Encyclopedia and Able Media :
Tragedy: form of drama in which a noble hero (the protagonist) meets a fate inherent in the drama's action.
Drama: a composition presenting a story in dialogue, to be performed by actors; a play.
Or:
Greek tragedy - a literary composition written to be performed by actors in which a central character called a tragic protagonist or hero suffers some serious misfortune which is not accidental and therefore meaningless, but is significant in that the misfortune is logically connected with the hero's actions. Tragedy stresses the vulnerability of human beings whose suffering is brought on by a combination of human and divine actions, but is generally undeserved with regard to its harshness. This genre, however, is not totally pessimistic in its outlook. Although many tragedies end in misery for the characters, there are also tragedies in which a satisfactory solution of the tragic situation is attained.
Tragedies are plays that have a common theme: humans dearing to defy the gods, fate, or societal order, and being punished for that, by paying with their own lives or losing those dearest to them. The punishment is usually administered in a symbolic or very dramatic fashion - suicide, violent death, etc.
"Argonautica" is an adventure, or epic poem, not a tragedy, even if it has its gory and tragic components. It's a collection of several adventures, with one (in this case) or more central characters at its core, like the Odyssey and the Iliad.
An epic is a long poem which tells a story involving gods, heroes and heroic exploits. Since the epic is by its very nature lengthy, it tends to be rather loosely organized. Not every episode is absolutely necessary to the main story and digressions are not uncommon. You will notice how different in this regard is the genre of drama, in which every episode tends to be essential to the plot and digressions are inappropriate.
*running for cover*