Which intervals can be perfect

The intervals C-E and C-Eb are both thirds. They sound different because they contain a different number of half steps. The third from C-E contains four half steps. The third from C-Eb contains three half steps. The larger third is called the major third, the smaller third is called the minor third. Quality is used to distinguish intervals of the same size but with different numbers of half steps.

The terms used for quality are:. Intervals are classified as perfect or imperfect. Unisons, fourths, fifths, and octaves are termed perfect intervals. Seconds, thirds, sixths, and sevenths are termed imperfect intervals. Perfect intervals are the unison, fourth, fifth, and octave. They occur naturally in the major scale between scale note 1 and scale notes 1, 4, 5, and 8. Imperfect intervals are the seconds, thirds, sixths, and sevenths.

They come in two forms, Major and Minor. Major seconds, thirds, sixths, and sevenths occur naturally in the ascending major scale between scale note 1 and scale notes 2, 3, 6, and 7.

Minor seconds, thirds, sixths, and sevenths occur naturally in the descending major scale between scale note 8 and scale notes 7, 6, 3, and 2.

Perfect intervals are never major or minor. Likewise, major and minor intervals are never perfect. If you expand or contract an interval by a half step you change its quality. The size may stay the same. The resulting quality depends on whether you alter a perfect interval or an imperfect major or minor interval. When you alter a perfect interval by a half step it becomes either diminished or augmented. When a perfect interval is made one half step larger it becomes augmented.

As a beginner you should therefore begin with Intervals and later continue with, for example, Melody dictation to identify a sequence of intervals, or Chord identification to identify harmonies with more than two tones. An interval is the distance in pitch between two tones. It is labeled by its numerical value and its quality. The numerical value indicates the number of tones of the diatonic scale it includes. In the staff above, the diatonic tones are shown i.

Examples of interval naming : The interval from C 1 to D 2 is a "Second" because it includes two tones, the interval from C 1 to E 3 and the interval from E 3 to G 5 are both a "Third" because they include three diatonic tones. Unison, fourth, fifth and octave are called perfect intervals.

Each of them can be diminished one chromatic tone smaller or augmented one chromatic tone larger. The rest of the intervals within an octave are: second, third, sixth and seventh.

Each of them can be major or minor. Below is an example of a perfect fifth, diminished fifth and augmented fifth and a major and minor third. Always count a note to itself as one when counting size. Example 2 shows the first 8 sizes within an C major scale:.

Example 2. Sizes of intervals. Size is considered generic. Example 3 demonstrates this:. Example 3. Generic size is demonstrated. Accidentals do not matter in the determination of generic size. A quality makes an interval specific when used in combination with a size. When speaking about or writing intervals, one says or writes the quality first and then the size. For now, we will only discuss three qualities: perfect, major, and minor. Different theorists in different locations and time periods have applied these qualities to different sizes of intervals, depending on milieu.

Example 4 shows how these qualities are applied today:. Example 4. Interval qualities. There are several different methods for learning to write and identify qualities of intervals. One method you may have heard of is counting half-steps. This is not a recommended method, because it is time consuming and often inaccurate. Example 5 shows two intervals. Try identifying their size and quality:.

Example 5. Two intervals. For the first interval: the notes are F and C in treble clef. Here is the process in more detail:. To review, there are five possible interval qualities, of which we have covered major, minor, and perfect:.

Augmented intervals are one half-step larger than a perfect or major interval. Example 6 shows this:. Example 6. Two augmented intervals. As you can see in the first measure of Example 6 , the notes F and C form a perfect fifth because C is in the key of F major. In the second measure of Example 6 , a major sixth is shown with the notes G and E because E is in the key of G major. Note that it is not always the top note that is altered.

Example 7 shows two augmented intervals in which the bottom notes have been altered:. Example 7. Two more augmented intervals. In the first measure of Example 7 , F and C again form a perfect fifth. In the second measure of Example 7 , G and E once again form a major sixth. Diminished intervals are one half-step smaller than a perfect or minor interval. Example 8 shows this:. Example 8. Diminished Intervals. In the first measure of Example 8 , the perfect fifth F and C has been made a half-step smaller, since the top note has been lowered by a half-step.

In the second measure of Example 8 , G and E form a major sixth which becomes a minor sixth when the top note is lowered by a half-step making the entire interval one half-step smaller. It is very important to note that major intervals do not become diminished intervals directly; a major interval becomes minor when contracted by a half-step. It is only a minor interval that becomes diminished when further contracted by a half-step.

Again, it is not always the top note that is altered. Example 9 shows two diminished intervals in which the bottom notes have been altered:.

Example 9. Diminished intervals with the bottom notes altered. In the first measure of Example 9 , F to C form a perfect fifth. In the second measure of Example 9 , G to E form a major sixth. Examples 10 and 11 again demonstrate and summarize the relative size of intervals. Each bracket in these examples is one half-step larger or smaller than the brackets to their right and left.