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Intervals - The Thirds

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Intervals - The Thirds

There are two main types of intervals: Consonant and dissonant. Consonant intervals sound pleasant, or at least comfortable. Dissonant intervals sound unpleasant, uncomfortable and even aggressive. We will come back to the dissonant intervals in later lessons. The intervals we have covered so far - the perfect interval - are all consonant intervals. The other consonant intervals are the thirds and the sixths. In this lesson we will look at the thirds, and the sixths will be covered in the next lesson. You should be familiar with the counting and naming convention, and you should know that the third is the interval from 1st to 3rd note. And you should find the rest of the thirds by applying some very basic mathematics: If the distance from 1st to 3rd is a third, then the distance 2nd to 4th, 3rd to 5th etc, are thirds too. There are two kinds of thirds: Themajor and minor third.

The major third

The major third is two whole steps above the root, which equals four frets on your guitar. The interval between the 3rd and 2nd string is a major third. The first major third in the C-major scale is C to E.

Go to my Ear Training Lesson for examples of the other major thirds in the C-major scale: F-A and G-B.

The minor third

The minor third is one whole and one half step above the root. It makes no difference if it is first a whole and then a half, as in the interval D-F, or first a half and then a whole as in the interval E-G.

As long as we use the C-major scale as the basis, we will not find a minor third within the scale, starting at the root of the scale. The third up from the root (C) is a major third. We go up one step to D, and choose the minor third interval D-F.
Go to my Ear Training Lesson for examples of the other minor thirds in the C-major scale: E-G, A-C and B-D.

Notice the writing of thirds in standard notation. Both notes are either on lines, or in spaces between lines. There is no space between the notes, but they are not overlapping.

We will of course play our C-major scale harmonized in thirds. But notice that we alternate between major and minor thirds. Listen to the sound. You may try harmonizing in major thirds or minor thirds only, just to listen to the effect.

The first third of a scale determines major or minor

It is the first third of a scale that determines if it is major or minor. If the first third is a major third, then the scale is a major scale. If the first third is a minor third, then the scale is a minor scale. There are many different scales. But at least if we do not choose too exotic scales, this rule applies to all of them.

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Previous page: Music Theory for Guitar - Music Theory for Guitar - The perfect invervals - sounds Next page: Intervals - The Sixths