Theory Thursday: Thirds

Intervals: The Third

Last week we learned that adjacent tones in a scale have the interval relationship of a second. And we also learned that if the second is made up of a single half-step (or one fret space on a guitar), it is called a minor second. Likewise, a second made up of two half-steps (i.e., two frets on a guitar), it is called a major second. Easy peasy, right?

This week, we're going to talk about the interval relationship that happens if you skip a tone. As you've likely guessed by today's blog title, it's called a third. So let's take a look at what the thirds look like in the A minor scale:

A -> C
B -> D
C -> E
D -> F
E -> G
F -> A
G -> B

None of that seems too bad so far, right? If we start on A, we simply leap-frog over the B to C, and we do the same for every tone in the A minor scale. Let's now take a look back at our pattern of whole and half steps that make up our A minor scale (I included the scale on top and the interval between each tone below...):

A B C D E F G A B C etc
 W H W W H W W W H  etc

Remember, every W is 2 half-steps. So let's now take a look at the raw intervals that make up each third interval in the A minor scale. We do this by adding adjacent intervals. So for example, A to C is W + H (using the pattern above), the B to D is H + W, C to E is W + W, etc. So this looks like:

A -> C : W+H = 3 half-steps
B -> D : H+W = 3 half-steps
C -> E : W+W = 4 half-steps
D -> F : W+H = 3 half-steps
E -> G : H+W = 3 half-steps
F -> A : W+W = 4 half-steps
G -> B : W+W = 4 half-steps

Remember how there are major and minor seconds? Well the same is true for thirds. A minor third (m3) is 3 half steps and a major third (M3) is 4 half steps.

Over time, you will naturally start to remember that A+C is a minor third. Right now, I don't think it's very important for you to memorize which thirds in the A minor scale are major or minor. What IS important is that you remember that minor thirds are 3 half steps and major thirds are 4. 

Review

• How many half-steps in a minor 2nd interval?
• How many half-steps in a major 2nd interval?
• How many half-steps in a minor 3rd interval?
• How many half-steps in a major 3rd interval?
• Try to list out from memory the A minor scale and write the intervals between each tone.

Reminder

These lessons are really intended to help you get a grasp on music theory. Things are a little slow moving at first because I'm not assuming ANY prior knowledge of this stuff. It's going to get a lot deeper as we continue. If you have ANY questions or comments, please leave a comment here, on my Facebook page, or tweet at me (@chrisstarkgtr).