We call the difference between one note and another an “interval”.
Common music scales consist of 7 notes that ascend in steps from the first note. Here is A minor (natural) ascending to the A an octave above and descending back again.
If we start with the note A, then the next note, B, is the second, so we say that the interval between A and B is a “2nd”. The third note is C, so the interval between A and C is a “3rd”, and so on.
G is the seventh (7th) note. The next note after G is another A, so we say that this higher A is the eighth note or “octave” (written as “8ve”) above the starting note A.
So the musical scale of A minor has 8 intervals:
Compare this with the scale of A major:
The major scale differs from the natural minor scale on the 3rd, 6th and 7th intervals where the notes are raised a semi-tone e.g. C in A minor is replaced by C# (“C sharp”) in A major. Similarly F becomes F# and G becomes G#.
Listen to the differences between the minor and major intervals:
To confuse the subject slightly, the 2nd interval of a minor and major scale is the same, but it is called a “major 2nd”. There is also a “minor 2nd” which is one semi-tone e.g. A to B♭. Why? Well although in the scale of A minor the 2nd interval A to B is 2 semi-tones, other intervals are only 1 semi-tone such as B to C, and E to F and these are called a minor 2nd.
Here are examples of the main intervals found in the A major and A minor scales. Note the table has 5 columns. If you cannot see all of them, swipe left to reveal “How it sounds”:
| Interval notes | On music stave | Number of semi-tones | Interval name | How it sounds |
| A to A |  | 0 | Unison | |
| B to C |  | 1 | Minor 2nd | |
| A to B |  | 2 | Major 2nd | |
| A to C |  | 3 | Minor 3rd | |
| A to C# |  | 4 | Major 3rd | |
| A to D |  | 5 | Perfect 4th | |
| B to F |  | 6 | Tritone | |
| A to E |  | 7 | Perfect 5th | |
| A to F |  | 8 | Minor 6th | |
| A to F# |  | 9 | Major 6th | |
| A to G |  | 10 | Minor 7th | |
| A to G# |  | 11 | Major 7th | |
| A to A |  | 12 | Octave |
Listen to different intervals. Which ones sound harmonious (the notes sound good together) and which ones sound discordant (the notes clash and don’t sound so pleasant together)?
You might notice that the minor 2nd interval (a semi-tone) B to C is very discordant. This is because the notes vibrate at frequencies that are close to each other but do not fit together very well.
The most harmonious intervals are the major 3rd, perfect 4th, perfect 5th and octave because the notes vibrate at frequencies that fit together very well in the ratios 4:5, 3:4, 2:3 and 1:2 respectively. See our page on Harmonics.
Tritones
Notice the interval B to F with 6 semi-tones is called a “tritone” because it is 3 whole tones, “tri” meaning 3 as in triangle, triple, triplet, etc.
Musicians tend to avoid harmonies that include a tritone because our brain wants to hear a “perfect” 4th (5 semi-tones) with a ratio of 3:4 or a perfect 5th (7 semi-tones) with a ratio of 2:3, and a tritone is close to both but fails to be either!
It is even known as the “devil’s interval” because it is considered to be so discordant (the notes clash against each other).
The tritone was featured in an episode of Doctor Who when it summons the evil Maestro who destroys all music with terrible consequences!
B to F is a 5th interval (B-C-D-E-F) but a semi-tone less than the “perfect” 5th of B to F#, and is therefore called a “diminished” 5th.
Another example of a tritone is F to the higher B which is a 4th interval (F-G-A-B) but a semi-tone more than the “perfect” 4th of F to B♭, and is therefore called an “augmented” 4th.
However, some music does use the tritone to create tension, so maybe it’s not quite so evil after all!
You can read more about intervals on simple wikipedia
See also our page on Harmonics
See also our page on How do Brass Musical Instruments work?
Now read our page on Why are there only 7 notes names A to G?
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