Jealousy is the theme every Othello essay touches — and the theme most essays flatten into "Iago makes Othello jealous, and then bad things happen." That's true, but it's not an argument, and it won't get you past the middle bands. A* answers treat jealousy as something Shakespeare is making a claim about, not just a plot mechanism. Here's a full theme breakdown, done the way it needs to be done for an A-Level essay.
The key idea: jealousy as self-consuming, not other-directed
Shakespeare's most important line on this theme is spoken by Iago himself, warning Othello about the very thing Iago is engineering:
"O, beware, my lord, of jealousy! / It is the green-eyed monster, which doth mock / The meat it feeds on."
Technique and effect (AO2): the personification turns jealousy into a predator, but a very specific kind — one that "mocks" its own food, meaning it never satisfies itself no matter how much evidence it consumes. This is the image to build a whole paragraph around: jealousy in this play isn't cured by proof. Othello gets his "proof" (the handkerchief) and it doesn't end his jealousy — it accelerates it. The monster metaphor tells you that in advance.
The dramatic irony point that's easy to miss: Iago says this line while actively creating the jealousy he's warning against. Students who flag this irony explicitly — that the warning is itself part of the manipulation — are showing examiners they understand Iago's method, not just his motive.
The second key quotation comes from Othello himself, once the jealousy has taken hold:
"Excellent wretch! Perdition catch my soul / But I do love thee! And when I love thee not, / Chaos is come again."
Technique and effect (AO2): "Chaos is come again" is a callback to the creation narrative — Othello is saying that Desdemona's love is the only thing holding his internal order together, and that losing it would return him to a pre-creation void. This is why the jealousy plot destroys him so completely: it isn't a wound to his pride, it's an attack on the only structure he has.
Page from the Othello A* Quote Bank — the Jealousy theme in full.
Putting it into a thesis
An A* paragraph on this theme doesn't argue "Iago causes jealousy." It argues something closer to: Shakespeare presents jealousy not as an emotional reaction to evidence, but as a self-perpetuating structure that consumes the very "proof" meant to end it — and then uses both quotations above as evidence, one from the manipulator describing the mechanism, one from the victim demonstrating it.
That's the whole theme, worked the way an examiner wants to see it: quotation, technique, effect, and an argument that treats the play as making a claim rather than just telling a story.
The full Othello A* Quote Bank covers seven more themes built exactly this way — Race & Identity, Gender & Power, Appearance vs Reality, Manipulation, Love & Marriage, Honour & Reputation, and Fate & Destruction — plus full character studies of Othello, Iago, and Desdemona, and an AO context page on Jacobean attitudes to race that most study guides skip entirely.