Like the major chord, 7th chords can be derived from the major scale. A 7th chord is obtained by adding the flattened 7th note of the scale to a major chord.
Note: the 7th chord is not indicated by Roman Numerals.
Because the notes of a dominant 7th chord are the first (I), third (III), fifth (b7) and flattened seventh (VI) notes of the major scaje, Uie diord formula for the seventh chord is: I III V b7