I have a couple students right now who are delving into the mysteries of "playing by ear," which roughly means to listen to a song and then be able to come up with the structure and changes and at least have a starting point for playing that song. Way back in my early years of playing I viewed that ability with awe. I had a friend who could do it and I supposed (with not a little jealousy) that he was endowed with some magical musical ability that I would never be able to understand. Well, maybe he was endowed with skills that made him an awesome player but after I went to college and began learning the basics of music theory much of the mystery disappeared. It can happen for you , too!
The first thing to understand is that just about all Western music for the last three hundred or so years has been based on the major diatonic scale. You know it: "do, re, mi, fa, sol, la, ti, do." From that major scale come many of the chords we play in American popular music. Before I go any further, understand that I'm talking about the less complicated forms of popular music like folk, country, blues and rock. Jazz is another thing entirely in that the diatonic scale is just a basic starting point and from there the player of that wonderful music goes in many, many directions.
To understand the major diatonic scale and the chords that are constructed from it you have to know a bit about intervals, which are the musical distances between the notes. It would be a wonderful thing if all the notes were the same distance apart but alas, that is not the case. For example, the notes C and D are what is called a "whole step" apart. Between them is another note, which has two names: C-sharp (C#) or D-flat (Db). Why does that note have two names? It has to do with the "key" a song is played in. Don't worry about that for the moment - just accept that the note between C and D has two possible names.
The interval between C and C# is a "half step" and the interval from C# to D is a half step so we say that C to D is a whole step. However - and here's the rub - the musical distance between B and C, and E and F, is a half step! In other words, for now, you can assume there is no B#, Cb, E# or Fb. (There is - those notes are really C, B, F and E, but you're not supposed to think of them that way in certain keys - more on that later)
Because of that lack of consistency in the intervals, to attain that "do -re-mi" sound of the major diatonic scale has to be adjusted depending on where you start and stop a scale. Here's the formula:
There are 8 notes in the scale if you move one complete "octave" from, say, one C to the next C higher up. Wait a minute! you say. Two C's ?!! Are they the same note?
Well, no...but yes! There are only seven "natural" note names in Western music: A, B, C, D, E, F, and G. There's no H! But there are literally hundreds if not thousands of notes that we can hear, from very low to very pitches so you can see that there must be many, many notes with each of those seven names.
You need to think of the names of the notes in a circular fashion. That is, moving through notes in sequence, after G comes A again. Keeping that in mind, here is a one-octave diatonic scale moving from C to the next C:
C - D - E - F - G - A - B - C
Now, remember what I said above about which notes are a whole step which are a half step apart and applying that to the C scale I just wrote, the intervals between the notes in that scale look like this:
whole - whole - half - whole - whole - whole - half
And THAT is The Formula of a Major Diatonic Scale! If you start with C and move to the next C, it happens that all the intervals between the notes line up perfectly with The Formula. Because of this, the Key of C Major (the notes found in the key of C) are ALL "naturals," i.e., no notes need to be raised or lowered ("sharped" or "flatted") to make that one-octave scale match The Formula!
For now, just re-read what I've written here in Part 1 and digest it. Read it a couple times if you need to! Next we'll look at adjusting notes to make all the keys. After that - the chords and how they are developed from the major scales.
Peace & good music,