Intervals

The distance that separates two notes is called the interval. This term also regulates the harmonic relationship between the two notes. It's very important to know the relationships between the notes, because we can build any type of scale or chord from these intervals. I suggest that you read and study this section carefully.
To know the interval between two notes, first of all you must have the MDS of the lowest note, after which we analyze the place where the other is found. You table below illustrates five categories of intervals (there should be seven, but we will look at the most common). The MDS is divided into sections in order to combine every degree of the scale with a determined interval. The five intervals are: PERFECT, MAJOR, MINOR, DIMINISHED and AUMENTED. We will use an example with the MDS of C, seen in the table below.

	DIMINISHED	MINOR	PERFECT	MAJOR	AUMENTED
I°			C
II°				D
III°				E
IV°			F
V°			G
VI°				A
VII°				B
VIII°			C

As you can see, the eight notes have been "distributed" in two categories. In the MDS, the I°, IV°, V° and the VIII° are considered perfects intervals, while the II°, III°, VI° and the VII° are major intervals. This distinction is made by the harmonic relationship that the various degrees have with the root (C). If we want to know the distance that separates the C from the E, we can say that we have a third major interval, which is equal to the physical distance of two tones (C - D = 1 tone,  D - E = 1 tone). Or the distance between C and B, which is a seventh major  interval. Now, in another scale the harmonic relationship is the same, which means that the root is always I° and so on for all the other notes that belong to their interval categorie. As an example, we will look at the scale of E major, and therefore the MDS of E.

	DIMINISHED	MINOR	PERFECT	MAJOR	AUMENTED
I°			E
II°				F#
III°				G#
IV°			A
V°			B
VI°				C#
VII°				D#
VIII°			E

As you can see, the notes of the scale are put in their appropriate places, and maintain any eventual alterations typical of the scale, either sharp (as in the scale of E), or flat, as for instance the scale of Bb that we see in the underlying table.

	DIMINISHED	MINOR	PERFECT	MAJOR	AUMENTED
I°			Bb
II°				C
III°				D
IV°			Eb
V°			F
VI°				G
VII°				A
VIII°			Bb

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