Music theory basics: from note names to triads

This course is for someone who already loves and maybe even plays music — you can find your way around a piano keyboard or a guitar, you can follow along by ear — but the theory still looks like a foreign language. People say "play it in G", "that's a minor chord", "watch the key signature", and you nod without really knowing what those words point to. This course fixes that, one small idea at a time, with no instrument required and no code — just the twelve notes and how they relate.

The whole subject is built from a tiny foundation: seven letter names, one measuring unit (the half step), and a couple of patterns. Once you see the foundation, scales, keys, and chords stop being memorized trivia and start being things you can work out.

By the end you'll be able to (course objectives):

• Name any note on a keyboard, including sharps and flats, and explain why C-sharp and D-flat are the same key.
• Measure the distance between two notes in half steps and whole steps.
• Count an interval by its number (a third, a fifth, an octave) from the letter names.
• Build a major scale anywhere using the whole/half step pattern, and say why C major uses only white keys.
• Explain why a key signature has the sharps it has, and recite the order sharps are added.
• Build major and minor triads and hear the single note that flips one into the other.

Prerequisites: None beyond curiosity. You do not need to read sheet music, own an instrument, or know any math beyond counting to twelve. A picture of a piano keyboard (or a real one) helps but is not required.

Practice environment: Everything is done with your eyes, ears, and a pen — or a free on-screen piano if you want to hear the examples. The exercises point at your own keyboard, your own playlist, or a piece of scratch paper; there is no embedded sandbox.

Lessons

Sources listed in sources.md.