Every composition makes an argument. The choice to place a headline at the top rather than the centre, to leave a large margin on the left, to position an image so it bleeds off the edge — these are not neutral decisions. Each one creates a reading order, suggests a relationship, and communicates something about the importance of what is being shown.
The classical principles of composition — rule of thirds, golden ratio, leading lines, negative space — are not rules in the prescriptive sense. They are descriptions of what the eye finds naturally harmonious, developed over centuries of visual problem-solving. Knowing them gives you a baseline. Knowing when to break them gives you a voice.
In UI design, composition is constrained by function in ways that poster or editorial design is not. The user has a task; the composition must support it. But this constraint does not eliminate compositional thinking — it elevates it. A login screen, a dashboard, a profile page each have compositional logic. The question is always: what should the eye see first, and what should it reach for next?