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Interval qualification
The qualification of an interval specifies its nature and its composition, that is to say the tones and semitones that form it.
Before you dive into this course, take the time to master the concepts seen in the courses on intervals and tones and semitones . Knowledge of the construction of the major and minor scales is also recommended, but not mandatory.
Perfect, minor and major intervals
The qualification terms of the intervals derive from the construction of major and minor scales. The qualifications are determined in relation to the first degree of the range (the tonic).
There are two types of intervals: perfect intervals and major or minor intervals.
Perfect intervals
Perfect intervals are intervals that do not vary, whether in a major scale or in a minor scale. So they have only one "normal" state, called perfect.
In the following figure, the upper staff represents the C Major scale. On the lower staff is the C minor scale with its accidentals (flats). The intervals are determined with respect to the first degree of the range, i.e., C. For example, the interval between C and F is the same in major as in minor. The interval between C and F is a fourth because there are 4 notes to go from C to F. So it's a perfect fourth.
Special case: the second is identical in both major and minor scales. But one often encounters the second degree lowered in a minor context (hence the flat in parentheses on the D of the minor scale): that is why the second is not considered as a perfect interval, but as a major or minor interval (see following paragraph).
The perfect intervals are the unison, the fourth, the fifth and the octave.
Major and minor intervals
Unlike the perfect intervals, the other intervals can take two different states, depending on the context. These intervals will be qualified as major if they belong to the major scale and as minor if they come from the minor scale.
For example, on the major scale, the third between C and E is larger than on the minor scale, because there is a flat on the E. The third is therefore a major or minor interval. The C-E interval is a major third while the C-E interval is a minor third.
The minor or major intervals are the second, the third, the sixth and the seventh.
To remember. A perfect interval is never major nor minor ; a major or minor interval is never perfect.
Warning: the major and minor scales are at the origin of the qualification of the intervals, but it is important to understand that one can meet major intervals in a minor context and vice versa.
Summary table
| Interval | Qualification |
|---|---|
| Unison | Perfect |
| Second | Major/Minor |
| Third | Major/Minor |
| Fourth | Perfect |
| Fifth | Perfect |
| Sixth | Major/Minor |
| Seventh | Major/Minor |
| Octave | Perfect |
The compound intervals meet the same criteria as the simple intervals. For example, a ninth being a compound second, it can be major or minor, but never perfect.
Diminished and augmented intervals
You may have noticed that we have not listed all possible intervals in the previous paragraph. For example, what to do with the interval C-F? What to do with the interval C-D? Admittedly, we saw that C-E is a minor third, C-D looks like this interval, but, if you remember the course on intervals, you know that C-D#_ is a second and the accidental (the sharp) on the D does not change that aspect. So, how to name these intervals?
Two qualifiers will be added to the qualifiers seen previously (perfect or major/minor). An interval smaller than a perfect or minor interval will be called diminished. An interval greater than a perfect or major interval will be called augmented.
Note that the "augmented" and "diminished" qualifiers can be applied to perfect intervals as well as to major or minor intervals.
Let's summarize the situation:
Diminished ← Perfect → Augmented
Diminished ← Minor / Major → Augmented
Augmented intervals
Let's take again the examples quoted at the beginning of the paragraph: C-F and C-D.
We know that C-F is a fourth because there are 4 notes to go from C to F. Previously in this course, we saw that C-F was a perfect fourth. F being higher by a chromatic semitone than F, C-F is greater than C-F. It is therefore an augmented fourth.
On the following keyboard, the perfect fourth is green. F (orange) is a chromatic semitone above F.
Let's now examine the case of the interval C-D. We know that C-D is a major second. D being higher by a chromatic semitone than D, C-D is greater than C-D. It is therefore a augmented second.
On the following keyboard, the major second is green. D (orange) is a chromatic semitone above D.
Diminished intervals
Now take the case of the interval C-G.
The C-G interval is a fifth because there are 5 notes to go from C to G. At the beginning of theis course, we saw that C-G was a perfect fifth. G being lower by a chromatic semitone than G, C-G is smaller than C-G. It is therefore a diminished fifth.
On the following keyboard, the perfect fifth is green. G (orange) is a chromatic semitone below G.
You may have noticed that, on the keyboard, the diminished fifth looks strangely like the augmented fourth seen previously. It is indeed the same keys that are pressed to play C-G and C-F. By ear, it is not possible to distinguish between the two. Yet, on paper, they are not the same notes, so they are two different intervals. The meeting of one or the other on a score depends on the context and the key signature. For example, in G major, which has a F in its signature, you will be able to meet the augmented fourth interval between C and F. On the other hand, in D Major, which has 5 accidentals in its key signature, whose G, one will find the interval of diminished fifth between C and G. This distinction is certainly theoretical, but it is very important, because it will allow you to apprehend the functions of notes and chords, thus to better understand the harmonic construction of a piece.
Let's end with a slightly more complex case, that of the interval C-B (double-flat).
The C-B interval is a seventh because there are 7 notes between C and B. At the beginning of this course, we saw that C-B was a major seventh and C-B a minor seventh. B being lower by a chromatic semitone than B, C-B is smaller than C-B. It is therefore a diminished seventh.
On the following keyboard, the minor seventh is green. B (orange) is a chromatic semitone below B.
Find the qualification of an interval
You now know all the qualifications of the intervals. You have to learn to recognize them for yourself. For this, there are several methods, each with its advantages and disadvantages.
The first method is to find the composition of the interval, that is to say the number of tones and semitones, to find its qualification.
Interval composition
The following table shows the composition of the main intervals.
| Interval | Composition |
|---|---|
| Unison | 0 |
| Minor second | ½ tone |
| Major second | 1 tone |
| Minor third | 1 tone and ½ |
| Major third | 2 tones |
| Perfect fourth | 2 tones and ½ |
| Augmented fourth/Diminished fifth | 3 tones |
| Perfect fifth | 3 tones and ½ |
| Minor sixth | 4 tones |
| Major sixth | 4 tones and ½ |
| Minor seventh | 5 tones |
| Major seventh | 5 tones and ½ |
| Octave | 6 tones |
To simplify, we have not distinguished between chromatic and diatonic semitones. For example, the octave is actually composed of 5 tones and 2 diatonic semitones.
To find the qualifier of an interval, first find its name and then identify its number of tones and semitones.
This table, although easy to understand, is difficult to use and memorize because it does not involve the tonal context from which the names of the intervals are derived. That's why we recommend the methods discussed below.
Intervals and keys
As we saw at the beginning of this course, the interval qualifiers come from the major and minor scales. The simplest and most logical way to find the qualification of an interval is to refer to the scale from which it comes.
For that, all you have to do is to look at the major scale whose first degree - that is to say the name of the scale - corresponds to the first note of the interval. If the desired interval is part of the scale in question, it will be a major or perfect interval.
To find the interval qualifier with this method, it is important to know how to find the key signature from the key (see the course on key-signature).
Let's take the E-G interval.
From E to G, there are 3 notes: E, F, G. It is therefore a third. We have the name of the interval, let's look for the qualifier now.
The first note of the interval is E. We will take a look at the E Major scale.
Let's look for the accidentals at the E Major key signature. Since the key name does not have any accidentals (no sharps or flats in the key name) and it is neither C Major nor F Major (both exceptions), we are going to look for key signature with sharps. In the sharp serie, we will have to stop on the note a semitone below E, that is to say D. The order of the sharps being F C G D A E B, in E major, the key signature will be composed of the following sharps: F C G D.
Here is, in the following figure, the E Major scale.
The G is present in the E Major scale. The interval E-G exists in the E Major scale: it is therefore a major or perfect interval. Since this is a third it can not be a perfect interval, so it is a major interval. The E-G interval is therefore a major third.
Be careful to always take into account the accidentals present in the key signature. In our example, the G is sharp.
Let's take the B-F interval.
From B to F, there are 5 notes: B, C, D, E, F. So it's a fifth. Let's now determine the qualifier.
The first note of the interval is B. We will take a look at the B Major scale.
Let's look for the accidentals at the B Major key signature. As the name of the key has a flat (the flat in « B flat Major »), we will look for key signature in flats. In the flat serie, we will have to add a flat after reaching the key name. Since the flat serie is B E A D G C F, in B Major, the key signature will be composed of the following flats: B E.
Here is, in the following figure, the B Major scale.
The F is present in the B Major scale. The interval Bb -F is included in the B Major scale: it is therefore a major or perfect interval. Since it's a fifth it's a perfect interval. The interval B-F is therefore a perfect fifth.
Let's take the B-A interval.
From B to A, there are 7 notes : B, C, D, E, F, G, A. So it's a seventh. Let's now determine the qualifier.
The first note of the interval is B. We will take a look at the B Major scale.
Let's look for the accidentals at the Si Major key signature. Since the key name does not have any accidentals (no sharps or flats in the key name) and it is neither C Major nor F Major (both exceptions), we are going to look for key signature with sharps. DIn the sharp serie, we will have to stop on the note a semitone below B, that is to say A. The order of the sharps being F C G D A E B, in B Major, the key signature will be composed of the following sharps: F C G D A.
Here is, in the following figure, the B Major scale.
The A is not present in the B Major scale. On the other hand, A is included in it. The interval B-A is therefore a amjor seventh. By lowering the A by a chromatic semitone, we get a minor seventh. The interval B-A is therefore a minor seventh. By further lowering the A by a chromatic semitone, we get a diminished seventh diminished. The interval B-A is therefore a diminished seventh.
Let's take the F-B interval.
From F to B, there are 4 notes : F, G, A, B. So it's a fourth. Let's now determine the qualifier.
The first note of the interval is F. We will take a look at the F Major scale.
Let's look for the accidentals at the F Major key signature. La tonalité de Fa Majeur fait parti des exceptions et possède un bémol à la clef sur le B.
Here is, in the following figure, the F Major scale.
The B is not present in the F major scale. On the other hand, the B is included. The interval F-B is therefore a perfect fourth. By raising the B by a chromatic semitone, we obtain an augmented fourth. The interval F-B is therefore an augmented fourth.
Last update on 2021/05/07
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