Creating chords for a song is much like building a house; you probably know the sort of style you want, but it is the chords that give the song it’s light and shade. And, in much the same way that the colour of your brickwork and windows will change the feel of your living environment. Adding major sevenths to chords can be the equivalent of letting in more colour and sunlight.
Basic chordal character and tonality is dictated by the third note of a triad, with this note expressing whether a chord is major or minor, or to put it another way, overtly happy or sad.
