Whenever you see a number after a chord, it refers to the note in that particular scale that you should add to the basic chord. If you know that the C scale (C, D, E, F, G, A, B, C), then C6, for example, is the basic C chord (C, E, G) plus the 6th, which is A.

But sevenths are a different matter. If you see a “Cmaj7,” then this would be C, E, G and B, which is the major seventh. A regular “7” chord means that you want to add a FLATTED seventh note - a major seven which is lowered a half step so that it is one full step below the root. So a “C7” would be C, E, G and Bb.

I go over the formation of these and other chords quite thoroughly in my columns The Power of Three and Building Additions and Suspensions. If you haven't already done so, you might want to give those a once-over.

Unlike a major or minor chord where the third is a major or minor third, the seventh chord is a minor seventh unless we specify that it is a major. If I say play an A, you automatically play an A major. If I say play an A7, we automatically add the G note (minor seventh) to the chord. Only if I ask for an Amaj7 will you play the natural seventh (G#).

In music theory, a seventh is traditionally used to make a transition from the root (or I) to the subdominant (IV). This transition is called a resolution. Even the use of this term “resolution” implies that a seventh chord is incomplete, that there must be a following chord that will bring it (and our ears) to a final point.

• Happy New Ear
• The Power of Three
• Building Additions and Suspensions
• Sevens Threes and Nines

• Seventh chord Wikipedia entry
• Seventh Chords Explained
• Seventh Chords Basic Concepts
• Theory on the Web: Chords