Introduction
An interval is what we call the "distance" between
two notes. This distance has two properties. One, the quantity, we learned
about in Lesson 1. The quantity is determined by counting the letters involved
in the interval. Count the first letter as one, and then count each letter
until the final letter is reached. The number of letters counted is the
quantity (or interval number) for that interval. Thus, three letters equals
a third, five letters a fifth, and so on.
The Quality of the interval is much more difficult. The quality is determined by figuring out the actual distance in steps. This allows us to differentiate between intervals of the same quantity. For example, c to e and c to eb are both thirds. We need some way to distinguish between these thirds. By labeling the interval number with a name, the quality, we can tell the difference between them. In this case, c to e is called a major third and c to eb a minor third.
Perfect Intervals
The
first intervals that we will look at will be perfect intervals. The reason
for calling these intervals perfect is too long to explain here. Just learn
which ones are perfect and you will be fine. Once you do some exercises,
it will become simple.
In defining perfect intervals, we begin by using a major scale. We define the intervals by using the first scale step, 1 , and the scale steps 1 , 4 , 5 , and 8 , as perfect intervals. For example: 1 to 1 is a Perfect Unison; 1 to 4 is a Perfect Fourth; 1 to 5 Perfect Fifth; and 1 to 8 is a Perfect Octave. (See Table 2-1)
Method 1: Using the major scale.
It is critical to understand that we must use the major scale of the
lower note in the interval to determine the quality. Intervals are defined
by using ascending intervals only, so using the scale from the upper tone
would often give us incorrect results. For example, if we want to find
the perfect fourth above f, we must first know the make-up of an
F Major scale. By looking at an F Major scale and counting up to the fourth
note, you will find that the fourth is a bb. This is
one of two ways to determine the notes in an interval.
Method 2: Counting Steps
It is also possible to figure out the intervals by counting half-steps
and whole-steps (see Exercise 2-1). By counting up four letters from f,
we find that a fourth above f is some type of a b note. Then, knowing
that a perfect fourth covers 2-1/2 steps, the b must be changed to a bb
because f to b is initially three whole-steps. Try using
both methods in the following exercises.
Exerise 2-2 Fill in the correct note names fot the intervals below.

Major Intervals
We
use the term major to label the rest of the intervals that occur within
the major scale. Since 1, 4, 5, and 8 were all used as perfect
intervals, that leaves us 2, 3, 6, and 7 to use as major
intervals. As with the perfect intervals, major intervals are defined by
going from the root note in the major scale up to the corresponding note
of the interval. As a result, a Major 2nd (M2) goes from 1 to 2,
a Major 3rd (M3) from 1 to 3 , a Major 6th (M6) from 1
to 6, and a Major 7th (M7) from 1 to 7. (See Table
2-2)
Exercise 2-4 Fill in the correct note name for the intervals below.

Exercise 2-5 In the following chord diagrams, fill in the diagram with the correct "dot" for the given interval. All intervals shall be ascending, so the note you choose should be higher in pitch than the note given. It is possible for the notes to be on the same string if necessary.

Minor Intervals
Now that we know how perfect and major intervals work, minor intervals
are easy. A Minor Interval is simply a lowered (or flatted) major interval.
For example, a minor 3rd (m3)* is a M3 that has been lowered one half-step.
When lowering the major interval, DO NOT change the note names (letters).
The note names must stay the same. Only the quality of the notes (#'s and
b's) can be changed.
At first, the easiest way to determine the minor interval is to figure out the major interval and then flat it. For example, a M3 above d is f#. Therefore, a m3 above d is f. Now try the exercises below.
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Augmented and Diminished Intervals
Now that we have covered all other interval types, we shall
cover augmented and diminished intervals. An augmented interval is either
a major or a perfect interval that has been raised a half-step. A diminished
interval is either a minor or a perfect interval that has been lowered
a half-step.
Pay careful attention to the difference in the affected intervals. Both augmented and diminished intervals affect perfect intervals in a similar way. They work differently when dealing with major and minor intervals. The augmented interval raises a major interval, while the diminished interval lowers a minor interval.
(Still Under Construction)