The collapsible list called 'Thematic Structure' or 'Map' in the leftmost column is an attempt to discover a plan, an underlying recursive structure of ideas that shapes the whole composition. I divided the poem into short segments (mostly less than 10 greek lines) representing - as much as possible - a single topic. These, the lowest level of my tree(1), I call 'segments'. These segments are gathered together (recursively) in groups called "themes" in such a way that they fit together naturally and bring out the organisation of ideas that govern the text. A theme can represent the simple topic of a segment or of a stretch of (child-)themes, it can also bring out the underlying theme in the more precise sense of the word of that part of the poem, especially on higher levels. It is often difficult to distinguish theme and topic. Different topics can have the same theme, especially within the same tree branch. This is important for interpretation, it can help us figure out what the local theme is. A task of the "explanation page" is to make clear these themes underlying different topics.
Boundaries are often not exact. The poet may change topic in mid-sentence or go through a number of topics in a few lines. Sometimes they are clear: beginning and end of a speech is almost always(2) beginning or end of a theme. So is a radical switch of focus or the beginning of a day. Speeches are most often introduced by a line identifying the speaker (“and answering him, Telamonian Aias said...”): sometimes such a line seems to belong to the preceding part, sometimes more to the speech. All this is not that important. What we have is an informal structure, a map for the singer. Formal precision is not in there.
In the battle parts of the poem it is more difficult to distinguish themata than in the speech parts. Consequently in many places I am less sure about the structure, especially on the lower levels. Still I am firmly convinced that the fault is mine, not the poet's, and that all battle topics have a theme and are not just surface.
There are three forms:
1) ring-structure, mostly tripartite (BAB) but sometimes having more rings (DCBABCD); the corresponding parts of these rings are related to each other by likeness or contrast. I will call the centre of the ring A, the closest ring B (B1 and B2), the next closest C and so forth. The outer, opening and closing themes, can be called R. Tripartite rings with a clear centre are the most common.
2) repeated sequences, such as BB or BCDBCD, possibly with an enclosing ring (R1BCDR1R2BCDR2, see 'embassies' 1.306-)
3) catalogues: longer sequences of similar themes (AAAA...), e.g. the catalogue of ships and men, the individual games in Patroclus' funeral games, the Epipolesis in book IV. These themes may have rather varying lengths. see e.g. the Epipolesis (Il 4.220) or the parts of Patroclus' funeral games.
The related parts of any ring structure may or may not have the same inner structure. In some cases they do: e.g. the "Truce and Duel" themes.
It is not true that the centre of a ring is always the main topic, the rings being comments
on it. That is the case as often as not and mainly on higher levels.
Apart from the likeness and contrast between corresponding rings
and the signalling of beginning and end of a theme or topic, I do not see any narratological
function of the ring structure.
The relative length of the corresponding rings varies quite a bit, but on the whole they remain reasonably balanced. If there is great disparity in length, there must be suspicion that my interpretation of the structure is wrong or that something else has intervened with the text.
This thematic structure is emphatically not meant to describe a formal structure, it is a - no doubt imperfect - attempt to recreate a plan of the poem, an inner structure to organise its composition and possibly to serve the singer as a memory-aid during performance. Writers who immediately write down what they compose do not need such an elaborate structure. Rhapsodes who only recite a part of the poem do not need it either. The listening public needs all its concentration to follow the singer - it has no time for structures. I see this as a composer's aid, to keep a handle on the material: created by an aoidos who composed this poem in his head, knew it by heart - he certainly did not improvise - and refined his poem and this structure over many years and many performances. In order to explain some anomalies in the structure, I prefer the "dictation" hypothesis more or less as advanced by Martin West and Oliver Taplin among others: the poet had already orally composed the Iliad (I am not talking about the Odyssey here) and had performed and improved it over many years, when (with the help of others) he managed to create a written copy of it, probably recomposing and expanding the already huge poem to something like the length that we have now. More about this here about writing and here about anomalies.
Another function of this map is that it shows the "seams" of the "stitched verse". This simplifies the adaption of the length of the recital to circumstances. I could imagine that a full performance of the poem as we have it now would have been rare because of the length of time it takes(1). This manner of composing makes it easier to adapt to the occasion, to make a selection of parts to perform and still give the public a complete experience.
Clearly, this analysis into themes
cannot be separated from interpretation ("what is the poet talking
about here?") and therefore not from subjectivity. We all know how even intelligent and
sensitive interpretation can produce an infinite number of wildly varying
results. Also the above method is vulnerable to a reproach of "begging the question": assuming
the existence of a structure to prove its existence. But, if I may use a metaphore, this is what a tracker of wild
animals does: the hunter assumes the passage of a beast to prove that it has been there.
The truth is not decided by this process but by the actual finding of the lion. Whether we
found it or not, whether we successfully hunted the Chimaera, is for others to judge.
It is true that discovering this structure entails identifying stretches of poem that are
about one topic or discuss one theme: this is not too difficult most of the time. But it also entails
identifying the corresponding themes, the B2 to some B1, the
likeness or contrast. In this there is no fixed rule to follow and arbitrariness may creep in.
Nevertheless there are also many themes where the likeness is on the surface and easy to see.
These must form the basis of our structure.
Experience teaches that the A, the central theme in a ring, is often a focus switch
e.g. from human to divine or from Achaean to Trojan. This helps,
but if and how the neighbouring themes should be grouped remains a judgement call.
Also, there are sequences of segments and themes that do not show an obvious structure, sometimes for more
than 40 lines. Possibly closer study or different segmentation would produce better results.
Therefore, since many eyes see more than two, it would be good if many other opinions
concerning this structure challenged mine. See the communications page for more info.
Surely we will never have exactly the same map that our poet carried around - this would be very unlikely. What matters is that we identify the important themes, the landmarks, correctly because we can use these for a better interpretation. So we work from the highest level to the lowest and vice versa in a dialectical process between interpreting and mapmaking.
The most interesting correspondences are those on a higher level that form a contrasting pair. For instance, the pair Diomedes - Achilles (the immortal -, the mortal hero), the aristeia's of Idomeneus and Patroclus (not going far enough - going too far, see Idomeneus' aristeia) or the first and the second half of Achilles' aristeia (the gods may help you - the gods may deceive you). These are three enormously important themes for the interpretation of the whole poem.
A low-level example: Odysseus' speech in book IX, trying to persuade Achilles to help the Achaeans:
9.223 comments on the "equal meal" (this really belongs to the previous theme)
9.228 (R) we will perish if you don't fight
9.232 (E) Hector is here, raging
9.247 (D) save the Achaeans, you'll regret it if you don't
9.252 (C) Peleus' words: put away quarrels, friendliness is best, it gives honour...
9.259 (B) put away your anger
9.264 (A) catalogue of gifts / these will be yours...
9.299 (B) ...if you put away your anger
9.300 (C) but if you hate Agamemnon and his gifts...
9.303 (D) pity the Achaeans, for they honour you like a god
9.304 (E) now you can get Hector who is raging
9.305 (R) no one else is up to him
Odysseus goes neatly from point to point till he reaches the
central statement, the catalogue of gifts. Then he works back through a
series of shorter points in reverse order to the starting statement:
"only you can do it".
Not all is ring-structure though. Achilles, in his answer to Odysseus, goes through the same series of points twice:
9.307 (R) Achilles: don't try to sweet-talk me
9.312 (B) I hate liars, I will not obey
9.318 (C) I gave him everything
9.332 (D) he took the girl from me
9.346 (E) Hector will beat you, but I will sail home
9.369 (B) tell the others: he cheated me
9.378 (C) I will not fight for any amount of treasure
9.388 (D) I will not marry his daughter
9.401 (E) I will take Thetis' advice and go home
9.421 (R) Tell the leaders their plan will not work
This repeated sequence with a closing ring could be summarized as RA1A2R
A special example of a repeated sequence is in the embassies sequences at the end of book I:
A good question is, whether the structural likeness also hides a meaning. Is the second theme in any way related to or a comment on the first? I think it is but I will clarify my point of view elsewhere.