In the Iliad, fate and the will of the gods are two distinct concepts. This is shown when Zeus is tempted to save his son, Sarpedon, from his predestined death in battle, though he ultimately chooses not to. However, in the Odyssey, fate and the will of the gods are merged: the majority of gods decrees that Odysseus will go home, and this is thus his fate. Additionally, Tiresias' prophecies are "what the gods wish." Why does this discrepancy exist, considering that the Odyssey is a sequel of sorts to the Iliad?
Fate is controlled by the Fates, whom no god can contradict. According to Walter Otto's The Homeric Gods (Walter F. Otto, The Homeric Gods: The Spiritual Significance of Greek Religion. 1929. Translated by Moses Hadas, Thames and Hudson, 1979), the Fates are a holdover from a primordial religious belief preceding the Olympians, including Chronos, Gaia, the Furies, etc. If the Odyssey was composed later, it makes sense for their job to be subsumed by the newcomers, rendering them superfluous.
The book's back in the library, so I can't find an exact quote, but this is the closest note I have:
Kindly and benevolent to those who remained loyal to them, terrible to any who--whether out of willfulness or necessity--disregarded them, they enclosed the life of the community and of the individual by their unalterable ordinances. They are a multiplicity but belong to the same realm, and they are not only related to one another but all flow together into a single large essence. This we can see in the divinities in which they are represented: all belong to the earth, all have a share in life as in death; whatever their individual traits may be, all may be designated as deities of earth and of death.
This marks the sharpest of distinctions from the new gods, who belong neither to the earth nor to the elemental in general and have no dealings with death. But the ancient world of gods was not forgotten even in later times and never wholly lost its power and its sanctity. --p17
It's also worth noting that Otto's approach reads the Homeric epics alongside earlier (and later) religious cult beliefs, so it's more cultural history than straight-up textual analysis--although his readings are in my opinion quite brilliant. For example, if we take (as he does) the gods to be the name given by the Greeks to a certain kind of thought or emotion that comes seemingly unbidden, then Athena, goddess of wisdom, is in "fact" the name for the reassertion of reason over emotion; hence, in the scene where Achilles swallows his anger against Agamemnon:
Athena suddenly touched him [Achilles]. The sense of her coming is the victory of reason. This describes her better than long discussions of her nature can do. --p48
Thanks to an altruistic commenter, I can now offer some more evidence from Otto. He does indeed group the Fates with the primordial religion:
All of this plainly indicates that we are dealing with denizens of that primeval world of gods whose earthiness and whose ties to earth distinguish them sharply from the Olympians. Like so many of the figures of that gloomy and austere sphere, the Moirai [Fates] too administer a sacred ordinance and are inexorable avengers of any who transgress it. --p267
And in that religion, the Fates primarily allotted death:
So the Moirai stand, in the sphere of the ancient earth-religion, as dark powers which determine death. Determination of death is the proper sense of the notion of allotment or share which the name Moira implies. --p268
But with the rise of the Olympians, the mechanism by which death is allotted is shifted almost wholly to the Olympians, so that they seem to act in accordance with a necessity:
The primeval image of the scales is therefore not employed by Homer with its original meaning; it serves merely as a visible expression of the necessity whose moment has now arrived. --p274
Instead of the actions of the Moirai,
A life which is finished is always [abandoned by its god and] destroyed by the tutelary deity of another life which is opposed to it. --p279
Hope this helps!
This is a complex subject, and worthy of a thesis, but I'll attempt to briefly address it.
The Sarpedon incident is interesting in that Zeus only contemplates altering fate. One could say that his ultimate decision to let Sarpedon die is a confirmation of the inviolability of fate. In the same way, the gods, most notably Poseidon, may argue about Odysseus' fate, but ultimately he does return to Ithaca.
You may find this video elucidating: Barry Powell, translator of The Odyssey, explains that fate is in the hands of the Gods and it overrides all circumstances. (Oxford University Press)
In Homer's Conception of Fate (James Duffy, The Classical Journal, Vol. 42, No. 8, pp. 477-485) the author asserts:
Homer does not state that the power of fate is disassociated from Zeus and that it is an independent power in itself. Anything that is effected by fate in the poems is also accomplished by the divine power which represents the highest deity, Zeus.
Duffy makes the point, regarding Calypso, that:
The poet says that it was fated for Odysseus to return to his home, but it was Zeus who ordered his release.
Fate or destiny cannot be looked upon in Homer as having its centre in the undefined or in power, nor does it acquire a personality which manifests itself by exercising a power beyond or above the gods. The prayers of the Homeric heroes are not addressed to fate or to any unseen power, but are directed to Zeus except for a few which are offered to other Olympians. No character ever expresses a belief in a power called fate by which Zeus and the other Olympians are confronted and which they cannot subordinate. The only solution for the much-discussed question of fate and destiny in Homer is to interpret it as an abbreviation of Dios moira (divine fate) or Dios aisa (divine fortune) as originating from Zeus and so regard fate and the will of Zeus as identical.
Duffy specifically addresses the Sarpedon incident. In the Iliad, Duffy's thesis would seem to be confirmed in that Zeus asks Hera whether he should save his son or kill him:
“Ah, woe is me, for that it is fated that Sarpedon, dearest of men to me, be slain by Patroclus, son of Menoetius! And in twofold wise is my heart divided in counsel as I ponder in my thought whether I shall snatch him up while yet he liveth and set him afar from the tearful war in the rich land of Lycia, or whether I shall slay him now beneath the hands of the son of Menoetius.”
SOURCE: Iliad, 16.433-438
The actual word used is δαμάσσω (damasso) in the first person, singular, subjunctive, as in "should I slay him".
In terms of the conception of fate differing in the two works, Duffy comments on this in the opening of his essay:
Homer's conception of fate or destiny generally engages the attention of critics and commentators. It is conceded by them that the poet's conception of fate is the same in the Iliad and Odyssey.
Regardless, you are in very good company in contemplating this subject!
I might venture that:
- Fate in the Iliad is primarily driven by Zeus' will
- Fate is the Odyssey is primarily driven by Athena's will
This is because Athena is the patron of Odysseus, and although Zeus is all-powerful, he states that Odysseus' deliverance derives from Athena:
Then Zeus, the cloud-gatherer, answered her, and said: “My child, what a word has escaped the barrier of thy teeth! Didst thou not thyself devise this plan, that verily Odysseus might take vengeance on these men at his coming?
SOURCE: Odyssey, 5.21-24
Athena, the favorite child of Zeus, influences her father to exert her will.
I think it's telling from a literary standpoint that these questions continually arise, and I'm not sure the ambiguity would have been unintended. Literature is generally strengthened by ambiguity in that different minds over many generations can interpret the work in different ways. Thus, ambiguity may be understood as a strategy to kindle and sustain interest--it serves the function of raising questions.
It's worth noting that Homer has subversive elements. While the Iliad and Odyssey reinforce the power of the gods, and of Zeus in particular, the works also undermine the gods in reducing their dignity (the gods are subject to the same foibles as humans, and do not always behave well,) while elevating the dignity of humanity (Hector, Andromache, Priam, Patroclus, Achilles) by showing mortals at their noblest.
Possibly Homer was undermining the power of fate by showing it is subject to the will of Zeus, but also making the point that fate is capricious in that it is a function of the whims of the gods.