The Many Faces of Intervals: An Interval Intro to Quality and Size

by KicknGuitar (Dec 19, 2007)

The Many Faces of Intervals
An Interval Intro to Quality and Size

Just a quick note, for those of you familiar with using flats (b) and sharps (#) with your intervals, this is more of a formal theory lesson. Don't be scared, it's quite easy to follow along if you are already familiar with the usage of sharps and flats with interval numbers like so, "1-b3-5, 1-3-#5-b7, 1-bb3-5." If you misunderstand these, jump to JazzMaverick's Interval exchange chart to help you along.

Intervals are the distance between two pitches and are categorized by two factors, size and quality.

Interval Quality
Intervals have a few qualities. They change by half steps, either going up or down.

Decreasing Half a Step: Perfect Intervals
Perfect intervals decreasing half a step become diminished.

Increasing Half a Step: Perfect Intervals
Perfect intervals increasing half a step become augmented.

Decreasing Half a Step: Major and Minor Intervals
Major intervals decrease half a step to become Minor. Minor intervals decrease half a step to become Diminished.

Increasing Half a Step: Major and Minor Intervals
Minor intervals increase half a step to become Major. Major intervals increase half a step to become Augmented.

              Decrease  Increase
Diminished- - - -Perfect- - - -Augmented
Diminished- - -Minor- - -Major- - -Augmented

Abbreviated intervals are,
Perfect - P
Major - M, Maj
Minor - m, min
Augmented - Aug
Diminished - dim

Some Don'ts on Intervals,
Minors never become Perfect.
Majors never become Perfect.
And vice versa.

Interval Size
Interval qualities go along side with specific interval sizes. Do you recall the Major scale? A major scale has seven different notes (the eighth note, or interval, is the octave of the first, hence it doesn't get counted to the total). It reads as follows,

 1    2    3    4    5    6    7    8    9   10   11   12
P1 M2 M3 P4 P5 M6 M7 P8 M9 M10 P11 P12 etc.

Lets try this out on some real notes,

To label an interval correctly we must know the lowest note and highest note.
In this example, our low note will be G and our high note will be A. Before we can figure out the quality of the interval, we must found the size. F is out initial note, and we must get to A, luckily for us, A is the next note. G (first) - A (second). We have just found the size of our unknown interval, it is a second. The question now is, what type of second? We simply take the major scale pattern and apply it to our unknown interval starting with the lower note. In this case the lowest note is G, so we now use the G Major scale,
Interval:P1 M2 M3 P4 P5 M6 M7 P8(P1)
Note: G A B C D E F# G

Here all we do is look for the second interval, A. The second interval of G Major is a M2 A. We now have something to refer to when looking up intervals. From here, we check to see if the second interval (A) in G Major is exactly the same as our second unknown interval (A). We have a match. Great, you're done. G to A is a M2. If our A was a Ab, we would have to see how many half steps our A was away from G Major's A. The step difference between Ab and A is one half step down. A half step down from a Major interval is a minor interval. Thus, G to Ab would be a m2, due to the half step decrease between Ab and A.

Practice this with any notes, or with any interval (asking yourself what is a dim5 away from F?)

Many times the quality is substituted with sharps and flats. Don't let this confuse you. When you have a "b3" it doesn't mean the actual note is has a single flat, just like a m3.

To convert the title "b7" to the interval gone over above is quite easy. Just like the previous tip mentioned above, the "b" doesn't mean the note will be flat, just the structure of the scale's intervals will be raised or lower a certain number of steps. When referring to a b7, you don't mean the seventh note is flat, you mean the seventh note is lowered half a step. Sharps and Flats refer to the distance the note is to be away from the interval.
In B Major,
B C# D# E F# G# A# B
1 2 3 4 5 6 7 8

To refer to the b7 is to say A, not Ab because the "b" next to the interval is saying move down half a step from the seventh interval. A flat next to a note means half a step below the note. The difference is in the context, the interval title 1,3, #5, b7 is set, the note names change for varying key. The seventh interval in B Major is A# (a half step above A). to make it a b7 interval we must lower it half a step because the interval is telling us to go one half step (b).

                         ->#6 ->#7
1 2 3 4 5 6 7 8
B C# D# E F# G# A# B