The_Complete_Idiot%27s_Guide_To_Music_Theory

In most cases, the type of chord is determined by the middle note—the third.
When the interval between the first note and the second note is a major third—
two whole steps—you have a major chord. When the interval between the first
note and the second note is a minor third—three half steps—you have a minor
chord.
It’s no more complex than that. If you change the middle note, you change the
chord from major to minor.
Read on to learn all about major and minor chords—as well as some other types
of chords that aren’t quite major and aren’t quite minor.
Major Chords
A major chord consists of a root, a major third, and a perfect fifth. For example,
the C Major chord includes the notes C, E, and G. The E is a major third
above the C; the G is a perfect fifth above the C.
Here’s a quick look at how to build major chords on every note of the scale:
Major triads.
There are many different ways to indicate a major chord in your music, as
shown in the following table:
Notation for Major Chords
Major Chord Notation Example
Major C Major
Maj C Maj
Ma C Ma
M CM
∆ C∆
In addition, just printing the letter of the chord (using a capital letter) indicates
that the chord is major. (So if you see C in a score, you know to play a C Major
chord.)
Chapter 9: Chords 113