Perfect Fifth and Perfect Fourth

by Vicente Rizzuti
(Caracas - Venezuela)

I am an older beginner piano student(70). My question is:

Why the fourth and fifth are called perfect?

Thanks a lot for your attention.

Comments for Perfect Fifth and Perfect Fourth

Perfect Fifth and Perfect Fourth
by: Ido from www.piano-play-it.com

Hi Vincente,

We classify the intervals by their number (unison, second, third, etc.) and their quality (perfect, major, minor, augmented and diminished).

We divide the intervals in to two groups:
Consonance - a combination of notes that sound pleasant and stable when played at the same time.
Dissonance - is a combination of notes that sound unstable and unpleasant.

The perfect intervals are – unison, fourth, fifth and octave.
We call them perfect intervals because they have a high level of consonance. The unison and the octave are actually the same note so of course they sound stable when played together. The fifth is also a most stable interval due to a special physical relation between the two notes of the interval.

Let's take for example the C note and a fifth above it - the G note. They produce a stable sound, a high level of consonance, while being played together (the reasons come from the laws of physics.). Therefore this interval is called a perfect fifth.
Now, if we invert this interval, what do we get? G, and a C above it. In other words we get the same combination of notes as the fifth, only now we call it a fourth. As you see, a fourth is a result of the same notes that have a special relationship between them. Therefore the fourth also belongs to the group of the perfect intervals.

I hope that I have helped you,
Ido from www.piano-play-it.com

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