Major and minor intervals
Some intervals are specified with the word 'perfect', while others are specified with 'major' and 'minor'. Intervals of 2nds, 3rds, 6ths, and 7ths are specified with major and minor intervals. Let's look at them one by one.
Below is a diagram of a keyboard for your reference.
2nd: major and minor
We will start with 2nds. A minor 2nd is basically a half step. Intervals like A to Bb, and F# to G are minor 2nds.
One thing we need to be careful about is that even though A to A#, and A to Bb may sound the same when you play, A to A# is not a 2nd. To make an interval of a 2nd, we have to have two different letters; going from an A to another A is not a 2nd.
A major 2nd is basically a whole step. Intervals like A♮ to B♮, and F# to G# are major 2nds.
3rd: major and minor
Major 3rds are same as 2 whole steps. Intervals like C to E, A to C# are major 3rds. You can also think of it as 4 half steps if that is easier for you.
Minor 3rds are same as 1 whole step and 1 half step, or vice versa. Intervals such as A♮ to C♮, or F# to A♮ are minor 3rds.
6th: major and minor
We will skip 4th and 5th for now because they are not associated with major or minor intervals.
Intervals such as A to F#, and G to E are major 6ths. These intervals are far away from each other so it is difficult to count how many whole steps and half steps are in between. Luckily, there is an easy way to figure them out if you play the violin or the viola.
Let's think about playing an A on the G string. Major 6th above the A is F# on the D string. How would you play those two notes? You would use the 1st finger for the G string, and the 2nd finger for the D string. The distance of the two fingers feels like you are playing a whole step with two different strings. And that's all you need to know to identify a major 6th interval. You place your fingers on your instrument, and they feel like a whole step distance on two adjacent strings, that is a major 6th.
Intervals such as A to F♮, and G to E♭ are minor 6ths. Again, it is difficult to think about how many whole steps and half steps are in between, so let's think about them on the fingerboard.
Let's play an A on the G string, and F♮ on the D string. You would use the 1st and 2nd fingers, and they feel like you are playing a distance of a half step with two different strings. That's a minor 6th.
It becomes much easier to figure out 6ths when you think of them on the fingerboard like this.
7th: major and minor
7ths are very close to an octave. When you add one more letter to a 7th, it will become an octave.
A major 7th is just a half step short from becoming an octave. Intervals such as A to G#, and C to B are major 7ths.
A minor 7th is a whole step short from becoming an octave. Intervals such as A to G, and C to B♭ are minor 7ths.
7th is a large interval that is not the easiest to figure out. In the next article, I will show you a trick to make it easier, but before that I'd like to explain the perfect 4th and 5th.