The Complete Idiot''s Guide to Music Theory

Definition
On a guitar, a half step is
the distance of a single
fret. A whole step is the
distance of two frets.
Note
While the half step is the smallest interval in Western music, music from
other parts of the world often contains intervals smaller than a half step.
Some Indian music, for example, divides an octave into 22 steps, each
about half as large as a Western half step.
Tip
You can use the step method to describe the intervals between two notes—
although once you get more than a few steps away, the counting becomes a tad
difficult. When you’re trying to figure out which note is seven half steps above
middle C (it’s G, in case you’re counting), it’s time to use another method to
describe your intervals. 
A Matter of Degrees
A more accepted way of describing intervals is to go back to the seven main
notes of a scale—and revisit the relative numbering method. You can use the
numbers of the scale to denote the basic intervals between notes, and thus apply
this numbering to any scale.
First Things First
As you learned in the previous chapter, you can use numbers to describe the
seven main notes in any scale. The first note is numbered one, the second note
is numbered two, and so on. This method of numbering actually describes the
seven 
degrees
of a musical scale.
There also are fancy musical names you can use in place of the numbers, which
you might run into in some more formal situations. The following table pre-
sents these formal degree names.

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Part 1:
Tones
Degrees of the Scale
Degree
Name
First (Root)
Tonic
Second
Supertonic
Third
Mediant
Fourth
Subdominant
Fifth
Dominant
Sixth
Submediant
Seventh
Leading Note
Eighth (Octave)
Tonic
There are a few more terms you need to know before we proceed. When two
notes of the exact same pitch are played by two different instruments or voices,
they’re played in 
unison.
Two identical notes with the same name, played eight
degrees apart, form an 
octave.
(The word octave comes from the Latin word
octo,
for “eight”—because an octave is eight notes above the beginning note.)
For example, if you go from middle C to the next C up the keyboard, that’s an
octave; F to F is another octave … and so on.
These musical degrees come in handy when you’re describing intervals between
notes. Instead of counting half steps and whole steps, you can simply describe
an interval by using these relative numbers.
For example, let’s say you want to describe the interval between C and D. If you
count C as number one (the first degree), D is number two and the interval
between them is called a 
second.
The interval between C and E (the first and
third degrees) is a 
third;
the interval between C and F (the first and fourth
degrees) is a 
fourth 
… and so on.
Pretty easy, once you get used to it!
The following figure shows the basic intervals, starting with a unison and end-
ing with an octave, with C as the 
root.
20
All this dominant and sub-
dominant stuff will become
more important when you
learn about chord progres-
sions in Chapter 10.