A minor 7th chord

What each note does

• A is the root. It names the chord and is the note your ear hears as home.
• C is the minor third, a half step below the major third (C♯). That one note is the whole difference between sad and happy.
• E is the fifth. It adds weight without changing the character, so it is the first note to drop when a voicing gets crowded.
• G is the flat seventh. It adds tension that pulls toward the chord a fourth above, the sound of blues and of a V chord heading home.