Eight months into learning piano and I still didn't know what "key" meant. Not the physical keys – the other kind. When someone said "this song is in the key of G," I'd nod like I understood. I did not understand.
I avoided theory because it seemed boring. Abstract. Who needs theory when you can just follow tutorials?
Turns out: everyone. Once I finally learned the basics, everything got easier. Patterns appeared everywhere. Songs made sense instead of being random collections of notes.
Here's everything I wish someone had explained to me in plain English.
There are only 12 notes. Total. That's it. Every piece of music ever written uses some combination of these 12 notes. Look at one octave on your piano – from any C to the next C. Count every key, white and black. You get 12.
The white keys are the "natural" notes: A, B, C, D, E, F, G. The black keys are sharps and flats. A sharp is one key higher, a flat is one key lower. So the black key between C and D can be called C# (C sharp) or Db (D flat). Same note, two names.
A scale is a group of notes that belong together. Like a family. They sound good when played in sequence or combined. The C major scale is the easiest – all white keys from C to C. Play them in order. That's a scale.
Why do certain notes "belong together"? Because of the pattern of steps between them. Whole step means skip one key. Half step means the very next key. Major scales follow a specific pattern: whole, whole, half, whole, whole, whole, half.
Start on C and follow that pattern – you get all white keys. Start on G and follow it – you get all white keys except F# (the black key). Same recipe, different starting ingredients. More on this in my deep dive on scales.
Now the "key" thing. When a song is "in the key of C," it means the song mostly uses notes from the C major scale, and C feels like "home." The music wanders around but keeps returning to C as its resting point.
Why does knowing the key matter? It tells you what notes to expect. If you're figuring out a song by ear, knowing the key narrows your options from 12 notes down to 7.
Chords are what changed everything for me. A chord is multiple notes played at the same time. Most chords have three notes. And here's what nobody told me at first: chords follow patterns. Once you know the pattern, you can build any chord instantly.
Major chord formula: start on any note, count up 4 half-steps, count up 3 more half-steps. That's your chord. C major = C, E, G (count 4 from C to E, count 3 from E to G). Works for every major chord.
Minor chord formula: flip the numbers. 3 half-steps then 4 half-steps. A minor = A, C, E. One note different from A major. That tiny change completely shifts the emotional feel. Major sounds happy, minor sounds sad.
I stopped memorizing individual chords and started deriving them from the formula. Way faster. Full breakdown in what chords actually are.
The most useful thing in all of music theory: the I-V-vi-IV progression. In C, that's C major, G major, A minor, F major. Play those four chords. Sound familiar?
"Let It Be." "No Woman No Cry." "Someone Like You." "With or Without You." Hundreds of songs use these exact four chords in this order. Once you recognize it, you hear it everywhere.
Why Roman numerals? They represent scale positions instead of specific notes. C is the first note of C major scale, so C chord = I. G is the fifth note, so G chord = V. This lets you transpose songs to any key – same progression, different starting point.
How much theory do you actually need? For casual playing, know your major and minor chords, understand keys, recognize common progressions. Maybe a weekend of focused learning.
MusicTheory.net is free and excellent. Hooktheory is great for understanding how chords work in real songs.
I regret avoiding theory for 8 months. All those tutorials would've made more sense. Learn it early.