Harmonic analysis of Beatles "Because"

The genius of this song is that there are few chords in the actual key it is written. By using techniques from classical music, borrowed chords and modulations, Paul McCarthy was able to create a hauntingly beautiful chord progression which is both familiar and fresh. This is the thesis of Howard Goodall's BBC documentary. It shows how the beatles welded the rift between Classical Music and Popular music by rediscovering harmonies that classical music abandoned in the early 20th century.

I love Goodall's ability to explain this complex innovation in ways anyone can understand.

Howard Goodall's
BBC Beatles Documentary

For the rest, 

you need to understand music theory and harmony. 

"Because" is in the Key of C#min. Starting in C#min ascending and descending arpeggios, it goes on to a D#min7b5, the 2nd of C#min scale, then to a G#major chord, A major, and resolving to C#min.

This is called a "Deceptive Cadence" in that the i iv v is followed by VI not i, fooling the ear. Note that the G# is not in the C#min scale, this is because there is an ascending 2nd interval root movement between V and vi, and as the base note moves up, the 3 other notes must move down to avoid parallel 5ths and octaves.

The song then goes to an A7 descending to an A13 which is nothing less than the A7 with an extension of the 6th. A13 is not in the C#min scale, but acts like a secondary dominant ( v/ii), or the V of D major scale. This precedes the modulation to the D major scale in the next chord. 

The D chord goes on to the Ddim chord, 1 b3 b5. Diminished chords work well as passing chords, in this case a half step above the C#min chord returning to the beginning of the song. 

The Bridge moves into the parallel key of C#maj but instead of going to the root chord C#, it goes to the VI in the key which is F#maj followed by V7 which is G#7, ending with a #5th note alteration of G#7 chord as it ends the bridge, and resolves to the C#min chord begining the final verse. 

"Because" chords are in Ultimate Guitar website at

https://tabs.ultimate-guitar.com/t/the_beatles/because_crd.htm

Intro: C#m C#m D#m7b5 G#7 A C#m A7 A13 D Ddim

Verse 1: 

C#m C#m D#m7b5 G#7 

Be-cause the world is round, it turns me on_________; 

 A C#m A9 A13 D Ddim 

Be-cause the world is round___. Ah_____. 

 Verse 2: 

C#m   C#m D#m7b5 G#7 

Be-cause the wind is high, it blows my mind_______; 

 A C#m A9 A13 D 

 Be-cause the wind is high____. Ah. 

 Bridge: 

(*This is an exception, the Ddim is played for one beat and the last three beats have no chord) 

 Ddim (none) F# 

 Love is old, love is new; (none) 

G#7            G#7 

Love is all, love is you. 

Verse 3:

C#m C#m D#m7b5 G#7 

Be-cause the sky is blue, it makes me cry________; 

A C#m A9 A13 D Ddim C#m C#m 

Be-cause the sky is blue____. Ah_______________. 

Outro: 

D#m7b5 G#7 A C#m A9 A13 D Ddim 

Ah_________________. Oo_____. Ah_____.