Before I make any music-themed posts on this blog, I want to explain a few technical terms that I expect I'll occasionally want to invoke. They're not difficult, but some readers may be unfamiliar with them or have only a vague notion of what they mean. I assume a passing familiarity with the layout of the piano keyboard. If you don't have a keyboard handy and find any of the descriptions below difficult to visualize (or "auralize"), try playing with the little Flash keyboard here. (If you don't have Macromedia Flash installed, there's also a Java piano here.)
The major scale
Most people, I think, know how to find middle C on a keyboard and know that, if you play the next seven white keys in sequence, up the keyboard, you'll spell out the do re mi scale familiar from The Sound of Music ("Do, a deer, a female deer, re, a drop of golden sun," etc.). The last note in that eight-note sequence is another C -- not middle C, but the C an octave (a span of eight notes) above middle C. That is, the do re mi scale -- a.k.a. the major scale -- has only seven notes in it; with the eighth note, you're starting the scale over again, only higher ("that will bring us back to do").
In this blog, I will refer to the notes of the major scale by number. So do is 1, re is 2, mi is 3, etc. Ti ("a drink with jam and bread") is 7, which brings us back to do, or 1.
If you play middle C, and then play the next four white keys, up the keyboard, in sequence, you'll get to G, or 5. But if you play middle C and then play the next three white keys down the keyboard, you'll also get to G, or 5. For every 1, there's a 5 above and a 5 below. There's also a 4 above and a 4 below, etc. And for every 5, there's a 1 below and a 1 above. Etc., etc.
An interval is the distance between two notes. We call the distance from 1 to the 5 above it a fifth: the total number of white keys you have to press to get from middle C to the G above it is five. The distance from 1 to the 5 below it, however, is a fourth: the total number of white keys you have to press to get from middle C to the G below it is four. Conversely, the interval from 1 to the 4 above it is a fourth, while the interval from 1 to the 4 below it is a fifth. The interval from 1 to 6 is a sixth, from 1 to 3 is a third, etc.
What's the interval from 5 to the 3 above it (from G to E)? Well, if middle C is 1, how many white keys do you have to press to get from the 5 below middle C (G) to the 3 above it (E)? If you can't figure the answer out in your head, try actually pressing the keys, and then check your answer against the one at the end of this post.
It so happens that the first line of the Christmas carol "Joy to the World" traces out the major scale -- from 1 back down to the 1 below it. Sing it to yourself: "Joy to the world, the Lord is come." You sing the word "joy" on 1, "world" on 5, "lord" on 3, and "come" on 1 again. If you play the eight white keys from the C above middle C back down to middle C in the right rhythm, you'll play the opening line of "Joy to the World."
But let's say that, instead of starting on a C, you start on the next white key above C -- i.e., D. Now, if you just play down the white keys, the tune will sound completely wrong. In order to make it sound right, you'll have to throw in some black keys -- specifically, at "to" and "lord".
If, instead, you started playing "Joy to the World" on E, you'd need four black keys to make it sound right, and if you started on B, you'd need five!
There's a fundamental principle here, one that I've found is not intuitive for nonmusicians. Of everything I've said on this page, it's the most important thing to remember (if you don't know it already): no two major scales use the same notes. If you start your major scale on C, you can use all white keys -- but that's not true for scales begun on any other note. If you start your scale on G or F, you need only one black key -- but it's not the same black key. That is, if you play "Joy to the World" starting on F, you'll need a black key at "the" -- B-flat; but if you play "Joy to the World" starting on G, you'll need your black key at "to" -- F-sharp. (Try it.)
So, a few definitions:
a melody is a set of notes played in sequence;
a chord is a set of notes played simultaneously;
music written in a particular key is music all of whose melodies and chords use the notes of a single scale.
If you play a piece that's entirely in the key of C on the piano, you'll use all white keys. If you play a piece that's entirely in the key of G, you'll use one black key: F-sharp. If you play a piece that's entirely in the key of F, you'll use one black key, but not the same black key: B-flat. Etc., etc.
If you play middle C, then play the next six notes up the keyboard (stopping just shy of the next C), you will have played seven notes total: each of those notes determines a unique major scale, so each of those notes determines a unique major key. You will also, however, have left out five black notes. Each of those notes also determines a unique major key. So there are 12 major keys total.
An experienced musician can tell from a handful of notes what key a particular piece is in. Indeed, she can tell from only three notes what key a piece is in, if they're the right three notes. For instance, there are seven different major keys that contain the note C: C, D-flat, E-flat, F, G, A-flat, and B-flat. But five of those -- the ones with "flat" in their names, plus F -- contain the note B-flat instead of the note B. So if a melody begins on C and moves to a B (not a B-flat), it is in one of only two possible keys: C or G. The C and G scales, in turn, differ by only one note: the C scale contains an F, but the G scale contains an F-sharp. So if a melody contains only three notes, and they're C, B, and F, then the melody must be in the key of C. (Note that, by contrast, if the melody contains the notes B, C, D, E, G, and A, it could be in either C or G.)
This post has taken me a lot longer to write than I anticipated, because I'm trying to be both accurate and accessible. I'll be back with more Music Theory 101 in the coming days.
Answer key: a sixth