Before we move on to chords, a few clarifications.

When I mentioned twelve names for notes in the chromatic scale, I was not thinking of the two possible names for some of the notes. It would have been more accurate to say that if you go from A to A (or C to C, Eb to Eb, etc.) one half step at a time you will cover twelve differently-named notes, then start repeating the note names.

A major scale in any given key, covering an octave, is the familiar (we hope) do-re-mi-fa-sol-la-ti-do.

Now, we'll talk about chords and how they are constructed.

Chords are combinations of three or more different notes. (Occasionally two different notes, properly called an interval, are used as if they were a chord.) The particular type of chord defines which notes of the major scale are used to form it. For examples of the different types of chords, we'll use the key of C. We must start with its major scale, and we'll assign each note an Arabic number for reference, as such:

  C  D  E  F  G  A  B  C  D  E  F  etc.
  1  2  3  4  5  6  7  8  9  10 11 etc.

A major chord (also called tonic chord), is comprised of notes 1, 3, & 5. Thus a C major chord (written C) has the notes C, E, & G.

A minor chord has the notes 1, 3b, and 5. Thus a C minor chord (Cm or Cmin) has the notes C, Eb, & G. You'll notice when going from an X major chord to an X minor chord on most instruments that you're changing just one note, lowering it a half step (although you may change more than one string on a guitar, for example, if that note is repeated in the way the chord is fingered).

A seventh chord (also called dominant seventh) is a major chord plus a flatted 7th note of the scale. In C, the 7th note is B, the flatted 7th is Bb. A C seventh chord (C7) has the notes C, E, G, & Bb.

There is a chord called a major seventh chord which uses the 7th note (unflatted). A C major seventh chord (Cmaj7) has the notes C, E, G, & B.

A C minor seventh (Cm7, Cmin7) has C, Eb, G, & Bb. A C minor major seventh (Cmmaj7, Cminmaj7) has C, Eb, G, & B.

A C sixth (C6) is a major chord plus the 6th note: C, E, G, & A. A C minor 6th (Cm6, Cmin6) likewise has C, Eb, G, & A.

A C ninth chord (C9) adds a 9th note (D) to a C7 chord. Its notes are C, E, G, Bb, & D.

A C eleventh (C11) adds an 11th note (F) to a C9: C, E, G, Bb, D, F. A C thirteenth (C13) adds a 13th note to a C11: C, E, G, Bb, D, F, A. On most instruments you run out of fingers or strings to play all of these notes, and certain ones are left out, sometimes the root (note 1--in this case C), sometimes the 5th (G), sometimes others. A C13th chord may not have all seven different notes when you play it, but it will have that 13th note, which gives it its essential character compared to, say, a C7. These higher number notes (9, 11, 13) are typically played at a high pitch--you don't generally see a 9th or 11th as the lowest note of the chord, where it might be called a 2nd or 4th, respectively.

Various other chords also have their definitions of which notes are used. Among these are diminished, augmented, suspended, and flatted 5th chords. I don't have all these chord formulas at my fingertips, but it's not hard to find books that show all these chords (and more!) in each key for a given instrument. These books are like chord dictionaries, and I highly recommend them. They're especially helpful in showing various options in forming a given chord (in other words, there are several ways to make a C minor chord on a guitar).

The same formulas apply to any key. An F major chord has the 1st, 3rd, and 5th notes of an F scale (F, A, & C). A D minor chord has notes 1, 3b, and 5 of a D scale (D, F, & A).

The "textbook ideal" is to have the notes of the chord correspond in pitch to their numbers. In other words, for a C chord you'd like the bass note to be C, with a higher E, and a higher yet G. Sometimes, however, these relative pitchs are rearranged, to form what are called inversions of the chord. Some inversions sound okay, some don't. For example, on a guitar one could play a C chord with the 6th string open (an E note). It sounds lousy. If that string is fretted to form a G, it sounds fine. So in this case the inversion with a G as the bass note is pleasant, the inversion with the E as the bass note is not.

Many instruments will typically sound more than three or four notes, so some notes of the chord are repeated. On a guitar, for example, a typical C chord using five strings has C, E, G, C, & E. Using six strings it has G, C, E, G, C, & E. An F chord can be played with four (F, A, C, F), five (C, F, A, C, F), or six (F, C, F, A, C, F) strings.

Knowing the formula for a given chord can help in understanding what you're doing with your instrument. For example, on a guitar, there are two commonly used variants of A7 which are one finger different from the basic A chord (E, A, E, A, C#, E). In one, the finger on the (3rd) G string is lifted, changing that note from A to G (giving E, A, E, G, C#, E). In another a finger is added to the (1st) E string to make it a G (giving E, A, E, A, C#, G). Each version has all four notes that comprise an A7 chord, and now you know why either one of those strings can be fretted differently from an A chord to make it an A7.

Next, typical chord progressions used in songs.