Welcome to the Interactive Primer — a single, growing tree of knowledge. Every idea lives on its own page and names the ideas it builds on, so the whole of learning links together into one map you can climb from the very first concept to the most advanced. This page is the root: everything reaches back to here.

Pick a branch to begin:

• Mathematics — the science of patterns: counting, change, shape and proof, and the toolkit every other subject borrows.
• Physics — the rulebook of the universe: why things fall, fly, glow and bang, all from a handful of rules.
• Computer Science — solving problems with step-by-step recipes a mindless machine can run perfectly.
• Applied Mathematics — maths aimed at the real world: pricing, modelling, optimising and predicting what happens next.
• Welcome, Instructors — if you'd like to build lessons rather than learn from them, start here.

Use the map above and below to see how concepts connect, and the menu (top right) to switch theme or language.