Ask HN: How Can I Learn Music Theory?

If you speak Spanish, I would highly recommend Jaime Altozano's YouTube channel: https://www.youtube.com/playlist?list=PLrNRWzkImhnyDJYrUe2h0...

Here's how I approach it: forget about all the historic naming like "perfect fifths" and just think in terms of the modern 12-note equal temperament. Every note is a number, e.g. 440 Herz = 69, the standard guitar tuning has strings from 40 to 64, etc. Every interval is an integer, up an octave is +12, major chord is a triple of {x, x+4, x+7}, minor seventh chord is {x, x+3, x+7, x+10} etc.

Then, as a the second game-changer, learn the circle of fifths. Start with a note like C, and keep adding +7 to it. You'll get FCGDAEBF#C#G#D#A# - note how the sharped notes repeat the pattern of the nonsharped ones, easy to remember. The "keys" and "modes" stuff is just intervals of seven consecutive notes on the circle. Say you choose FCGDAEB, that's one key, then every mode is to be found by choosing one note out of those seven, and hopping over one note until you play all seven once: e.g. FGABCDE is one mode (Lydian afair), EFGABCD is another one etc. The "major" and "minor" keys are just different names for two of those seven modes. Pentatonic scales are those same modes with some notes omitted. Blues and harmonic minor scales are those same modes with some notes inserted. Overall modes, not keys or chords are the key to actually composing music intelligently, so learn them and learn to play them.

This should give you a good start in practical music theory.

> Here's how I approach it: forget about all the historic naming like "perfect fifths" and just think in terms of the modern 12-note equal temperament.

You actually want to learn these names, because they characterize the diatonic scale. Basically, pick seven contiguous notes on the circle of fifths, you get the pitch-class set of a diatonic scale. Then put the notes in the set in pitch order, and pick a tonal center. The default, naïve choice (pick the "flattest" note as your tonal center) is called Lydian mode. It can be interesting, but it has a drawback in that it forgoes the subdominant relationship. Picking the next-to-'flattest' note gives you Ionian, which solves this (the fourth scale degree forms a "perfect fourth" with the tonic, which is the flip side of a perfect fifth. Having more notes that can be related to the tonic makes for more musical possibilities). This is one simple explanation of the diatonic scale we ordinarily use.

One other quirk that also explains the "weird historic names": in traditional music theory, sharps and flats are definitely not treated equally, the way that would be implied by 12-equal temperament. The musically-relevant distinction is simple enough to explain: taking one example, F# "wants" to step up to G, whereas Gb "wants" to step down to F. This means that the "circle of fifths" turns into more of a helix of sorts that can be extended in both directions, in principle indefinitely. This difference cannot be "heard" directly; it's all about characterizing how the notes "work" in a piece of music.

After learning about the diatonic scale degrees, the next sensible step would be to start learning about counterpoint, which is based on simple definitions of consonance and dissonance between scale degrees. Then move on to thoroughbass and harmony.

Nitpick, but the bass part does not always play the root of a chord in the proper sense - "inversions" (which are actually very common) are precisely those chords where the bass is playing some note other than the root. What is true however is that the bass part provides the broadest level of "structure" in a piece of music that can be directly read in the score. Notes in other parts are always (at some basic structural level, disregarding further elaboration) chosen based on how they "relate" to the bass according to the rules of counterpoint.

The "thoroughbass" is a historic way of thinking about the "accompaniment" of a piece of music that's based on these principles; a "thoroughbass part" writes down chords by "annotating" a bass line with intervals, and music pieces can be written as "lead line(s) plus thoroughbass part" in a way that's comparable to a modern lead sheet but a lot more theoretically founded.

Yes, the names are important for "interop" reasons and yes, historically they mattered because the temperament was different and C# was totally different from Db. And yes, not all modern music is based on the 12-note equal temp. But for a beginner, I would advocate avoiding them and thinking in terms of semi-tones as I've described. It's simpler, and it's the way guitars and pianos and DAWs and whatnot work, so it's a good way of thinking for a beginner. I know for sure I didn't appreciate being bombarded with names like "augmented fourth" or "diminished seventh" when "+6“ or "+9" would make more sense in terms of piano keys/frets that beginners usually have in front of them.