What are fourths in music?
Fourth as a note in scale
In music, the fourth means the fourth note of a scale. Please note (pun intended), that it doesn’t automatically mean that the first and fourth notes of each scale create the perfect fourth interval. Knowing how to find the fourth note in different keys is very important. This note is a part of many important chords, such as II minor chord, subdominant chord, sus 4 chord and e.c. Just remember the fourth as an interval is a different thing. Let’s explain!
Fourth as an interval
The fourth or “perfect fourth” is the musical interval between two notes/pitches located at a distance of two tones and one halftone from each other. Simply put, one tone is the distance between two neighboring notes on the piano keyboard separated by one black key. A halftone is the distance between two neighboring notes, which don’t have a black key in between.
How to find the perfect fourth?
Let’s find a Fourth interval from C. The main thing we will be guided by is the distance of 2,5 tones. Check the piano keyboard to make it more clear.
We’re going up from C to D, crossing one black key and getting one tone. Then from D to E — there is another black key — another tone. So, two tones in total until now. Remember we need two and a half tones. Let’s go further, E – F — there is no black key. Therefore we got a halftone. So, we collected two and a half tones and we stopped on F. We’ve just found the perfect fourth interval from C. Playing C and F at the same time, you can hear the perfect fourth interval!
How to find the fourth in different keys?
The keys may be different, but the way to find the fourth from any desired note is the same, as we described above: you have to count tones to get the right distance between notes, which will create the perfect fourth interval.
Here is the list of perfect fourth intervals in C major scale and universal roman numerals:
Perfect fourths in C major scale
Perfect fourths in any major keys
C – F;
D – G;
E – A;
F – B;
G – C;
A – D;
B – E.
I – IV;
II – V;
III – VI;
IV – VII;
V – I;
VI – II;
VII – III.
Roman numerals indicate an order on notes in scale. In case of C major scale, roman numerals are:
Now you can number any major scale and find all perfect fourths there.
How to find the fourth in a minor scale?
Since we have three types of minor — natural minor, harmonic minor and melodic minor — it’s impossible to make a universal formula for all of them. But don’t worry! The most important thing is that now you can find your perfect fourth interval from any desired note, since you know, that this interval is two and a half tones. So, you need just to count tones.
With this knowledge you can find the perfect fourth interval in any major or minor key. Just be careful, when you start counting from your initial note, the note you come to may not belong to the scale you’re in.
Perfect fourth extra example
For instance, we’re in C natural minor. And we want to find the perfect fourth from “Ab” note. Let’s start counting: Ab-Bb – 1 tone; Bb-C – 1 tone; C-D – 1 tone. But we need just a half tone to accomplish two and a half tones. Therefore, we’re landing on Db, because C-Db – a hal tone. So, the perfect fourth from Ab will be Ab-Db. As you can see, Db is not in C natural minor scale.
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