Section 1--The major and minor scales
Hundreds of years ago, cassical composers used the "modal" system. Dorian, Hypodorian, Phrygian, Hypophrygian, Lydian, Hypolydian, Mixolydian, Hypomixolydian, Aeolian, Hypoaeolian, and Ionian were the modes used back then and music was primarily based around the use of scales. At the dawn of "tonal" music (music theory still used today to analyze and create music) composers such as Bach and theorists such a Jean-Phillipe Rameau began to narrow this down to simply Ionian and Aeolian, and renamed them the major and mino scales.
Major scale: 1-2-3-4-5-6-7 or WWhWWWh*
Minor scale: 1-2-b3-4-5-b6-b7 or WhWWhWW
*If I haven't already explained this in previous lesons, a "whole step" or a tone is the distance between 2 notes where there is one in-between. From C to D is a whole step up. From C to Bb is a whole step down. From F to G is a whole step up. From A to G is a whole step down. And so on. A half step or semitone is the distance between 2 notes right next to each other. B to C is a half step up. D to Eb is a half step up. And so on. Sometimes you'll see scales spelled out by their whole-step/half-step pattern.
Let's construct a Cmajor scale. C is our tonic, 1, so we go up a whole step to 2, D, up another whole step to 3, E, up a half step to 4, F, up a whole step to 5, G, up a whole step to 6, A, up a whole step to 7, B, and up a final half step to the octave 8, C.
Let's construct an Eminor scale. Start with E, 1, go up a whole step to , F#, go up a half step to b3, G, go up a whole step to 4, A, go up a whole step to 5, B, go up a half step to b6, C, go up a whole step to b7, D, and go up a final whole step to the octave 8, E.
When writing modern music, we start with a key.
Homework: before moving on watch the musictheory.net videos under the category "Scales and Key Signatures."
Let's say we're in the key of Gmajor. The Gmajor scale is made of the notes G-A-B-C-D-E-F#. This doesn't mean we can't use notes like C# or F or Bb. We can still use any note we want, but the thing that makes it the key of Gmajor is that your harmony (chord progression) will eventually "resolve" to the Gmajor chord, or will feel like it wants to resolve there.
What is resolution in music? When you play the chord progression Bminor, Emajor, Amajor, there is a feeling that the Amajor chord is a sort of home base. It's something you just hear as a musician. This is where the song wants to end, but there are other interesting things you can do. Just because the song WANTS to end on Amajor, doesn't mean it has to. If you ended the song on Fminor, even though the key of the song is Amajor, it might create an interesting effect.
Back to our Gmajor song...The key signature (which you should know from the videos) will show you that there is an F#. So when writing the sheet music, instead of writing the sharp sign (#) every time you want to play an F#, you just write the note where the F is and the reader already knows that it is sharped. If you want to play an F natural, you'll have to put the natural sign in front of the F (the sign that looks like a square). Just remember, if you put that natural sign there, it means that all the Fs throughout the song are natural, until you put the sharp or flat sign there again (# or b).
You can also alter all of the other notes. If you want to use a C# instead of a C, just use the sharp sign, but remember that the C will stay sharp for the rest of the song unless you put a natural sign there again.
Section 3--Diatonic Harmony
Diatonic harmony means that all of the notes for all of your chords fit a diatonic scale. A diatonic scale is a seven-note scale comprising five whole steps and two half steps, in which the two half steps are separated from each other by either two or three whole steps. The major scale and the minor scale are diatonic scales. So how do we make sure all of our chords are diatonic? Let's start with the Dmajor scale.
Now we stack "generic 3rds" onto each note. A generic 3rd is a 3rd when we don't know yet if it's a major or minor 3rd (3 or b3). Check the videos on musictheory.net under "intervals."
The 3rd of D is some kind of an F. The 3rd of E is some kind of a G. Work all this out and you end up with:
Now we have to turn these "generic intervals" into "specific intervals" which match the key signature. According to the key signature, all notes are natural except for C and F, which are both sharp. So we go back to those 3rds and make sure all of the Cs and Fs are shap and that all the other notes are natural.
Now we stack our next 3rds on top of those. The 3rd of F# is some kind of A. The 3rd of G is some sort of B. And so on...
Again, make sure all the Cs and Fs are sharp.
So the triads we end up with are:
1: D-F#-A (1-3-5)
2: E-G-B (1-b3-5)
3: F#-A-C (1-b3-b5)
4: G-B-D (1-3-5)
5: A-C#-E (1-3-5)
6: B-D-F# (1-b3-5)
7: C#-E-G (1-b3-b5)
This pattern can be applied to the major scale in every key using these roman numerals:
What do these mean? Well they're simply the numbers 1-7 in roman numeral form, each representing a scale degree. The capitol letters mean major chords, the lower case letters mean minor, and the chord with the 0 next to it is diminished. Let's apply this to the Fmajor scale:
Diatonic harmony can get boring, so I'll teach you how to use other chords not in the key eventually, but first you have to have a solid grasp of diatonic hamony and how to create chords larger than triads.
Homework: Watch ALL of the rest of the musictheory.net videos, starting on the category "Chords" and finishing on the final video of the category "Neapolitan Chords." There is some very important information here and you need to know it in order to understand my next lessons!