1. The gnomon (often seen through his use of ellipses). At the start of Dubliners, he introduces the Euclidian term without definition, but it's a term/technique he'll use throughout the rest of that work and others. The gnomon is the shaded piece of the sundial. It's the missing piece that defines everything. The moment one person says "I love you" for the first time, and then ...
Joyce really understood how what is not said may be far more powerful than what is said, and uses ellipses to force the reader to...
2. Recurring motifs. While most writers will riff off a few motifs running throughout a work, Joyce composes symphonies. Each time a motif is brought back, a new layer of depth/complexity is added, and with so many motifs running simultaneously with their own arcs throughout a work (In A Portrait of the Artist as a Young Man there are probably hundreds from birds, to Priests, to Romantic poets, to the color green, to...) the symphony is constructed and subtle complexity is achieved.
3. Euphony. The final passage of "The Dead" in Dubliners might be the most beautiful one ever written (if you haven't read it, do yourself a favor and read it!), and so much of that beauty is derived from its long vowel and repeated soft consonants. It's not just that it sounds pretty that matters, though, it's the placement. The story "The Dead" is a condemnation of Ireland's full political paralysis and what better way to leave the reader than to have been lulled to sleep himself. At the end of the second chapter of A Portrait of the Artist as a Young Man, the euphony takes on a different purpose. After a first establishing shot of a garden in the chapter, and a number of references to anticipating a falling away of innocence, the end of the chapter happens when protagonist is losing his virginity to a prostitute and the passage becomes engulfed with the soft s's not unlike the hiss of a snake. Brilliant, Joyce, so brilliant to drive home the final blow of a garden of Eden allusion with such temptingly euphonious hissing.
4. Perspective/voice. In the collection of short stories Joyce uses to talk about Dublin's gradual loss of power, he begins in first person and after a selling out scene, he uses third person, removing the voice of the person and putting it in the hands of another. In his loose autobiography, Joyce uses a third-person that grows with the protagonist as though he's suggesting that there is no "all knowing" voice outside of oneself. He ends with diary entries once the character establishes his own "voice."
5. Structure. In Ulysses, Joyce overlays the structure/plot of The Odyssey/Ulysses onto an ordinary man on an ordinary day in Dublin. Brilliant. In A Portrait of the Artist as a Young Man he uses a chiasmus structure (ABCCBA) alluding to Biblical poetry, but also allowing for commentary on growth each time a scene is mirrored and a chance to put silence in the center to suggest that silence is the ultimate mirror. Such a cool perspective on an auto-biography. In Dubliners, he takes unconnected stories of average Dubliners to show the gradual loss of power/hope of the city--talking about political strategy via an ordinary domestic abuse victim (Eveline)--brilliant. Finnegan's Wake, too, in its re-telling of all the other stories in various forms driving home the repeated motif idea of our lives as a series of stories we're constantly re-telling/revising as we go. He's a master. End of story.
