Why did Bruce use the seventh chord?

For the blues chord of 12, it is generally a group of three different chords played on the combination of 12:

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Four four one one one

Five four one one or five

Here, Roman numerals represent harmonious scales. For example, if you play F major, the chord order is:

F F or Bb F F

Bb Bb F F

C Bb F F F or c

In this example, f is harmony and Bb is subordinate. It should be noted that in most cases, chords belong to the seventh chord. Generally, the last chord is the main chord of the next harmony in the harmony series (here in C major).

Lyrics usually end in the last beat of the tenth bar or the first beat of the eleventh bar, and the last two bars serve as a transition for the instrument players. The chords of these two bars can be very complicated, and sometimes it is impossible to analyze their chords. But the last beat is almost always based on the seventh chord to improve the power of the next lyric.

In melody, Bruce uses semitones in three, five and seven flat major. Harmonic progression in the poem 12 has been used for centuries. Bruce's revolutionary improvement is to use three, seven or even five flat notes in the melody, and directly play adjacent notes and "tearing notes" (like leading notes) at the same time. A classical musician usually plays the lead first, while a blues singer or harmonica player will adjust the pitch. A blues pianist or guitarist will play both notes at the same time, and then release the lead in advance. Blues chords will also replace the main theme with minor seventh chords and major seventh chords. Bruce occasionally uses a minor. Bruce's minor is not much different from traditional minor. He occasionally uses flat five in the main melody, and often the singer or the main instrument will play the big five in the chord at the same time. In addition, the minor blues is generally 16 bar instead of 12 bar, which is often influenced by evangelical religious music.

Bruce's rock rhythm is also a major feature. Its use strengthens the effect of rhythm and reaction. Many postwar electronic blues and rock music used one of these simpler rhythms. The early Bebop is a basic repetitive fragment, which consists of three notes based on guitar strings. This sound group, combining bass and drums, creates a technique similar to bass walking, giving Bruce his typical feeling. The last bar of a harmony usually changes to the beginning of the next harmony. Rock rhythm is often accompanied by the sound of "duo, duo, duo, da" or "dong, da, da, da". On the guitar, it can use a simple, constant bass or turn from the fifth chord to the seventh chord step by step, and then turn back.