Month three. I could play C, G, and F chords. But I had no idea why those notes went together. Just memorized finger positions like phone numbers.
Then someone showed me the formula and everything clicked.
A chord is multiple notes played simultaneously. Most basic chords have three notes – these are called triads. The notes aren't random. They follow a pattern based on the root note.
Major chord formula: Root + 4 half-steps + 3 half-steps.
Let's build C major. Start on C (root). Count up 4 half-steps: C#, D, D#, E. Land on E. Count up 3 more half-steps: F, F#, G. Land on G. C major = C, E, G.
Now G major. Start on G. Count 4 half-steps: G#, A, A#, B. Land on B. Count 3 more: C, C#, D. Land on D. G major = G, B, D.
Same formula, any starting note. I stopped memorizing chords individually and started deriving them.
Minor chord formula: flip the numbers. Root + 3 half-steps + 4 half-steps.
A minor: Start on A. Count 3: A#, B, C. Land on C. Count 4: C#, D, D#, E. Land on E. A minor = A, C, E.
Compare A major (A, C#, E) to A minor (A, C, E). One note different. That tiny change – C# versus C – transforms the entire emotional feel.
Why do chords work? Without going deep into physics: certain frequency ratios sound pleasant together. The major chord ratios happen to be particularly consonant. Our ears evolved to find them agreeable. The math behind this is interesting but not necessary for playing.
Chord progressions are sequences of chords. Some sequences appear constantly because they sound good. The I-V-vi-IV progression in C: C, G, Am, F. Play those in order, loop them. Sound familiar? Hundreds of pop songs.
The Roman numerals refer to scale positions. In C major scale, C is the 1st note (I), D is 2nd (ii), E is 3rd (iii), F is 4th (IV), G is 5th (V), A is 6th (vi), B is 7th (vii). Capital means major, lowercase means minor.
This system lets you transpose. I-V-vi-IV in G is G, D, Em, C. Same progression, different key. Same emotional journey, different notes.
Seventh chords add a fourth note. C major 7 = C, E, G, B. Dominant 7 (like G7) = G, B, D, F. These add color and tension. Learn them after triads feel solid.
Inversions: same chord notes in different order. C major = C, E, G (root position). E, G, C = first inversion. G, C, E = second inversion. Same chord, different voicing. Useful for smooth voice leading between chords.
Practical application: Most pop songs use 4-6 chords. Learn the common ones in C and G major. C, G, Am, F, Em, Dm covers probably 80% of what you'll encounter. Then learn to transpose using Roman numerals.
For how this connects to actually playing songs, see easy songs that use these chords. And Hooktheory lets you see what chords famous songs use.