The blues genre of music originated in the USA in the 19th century and was a form of music developed by African-Americans. It is described as a soulful and emotional music whose themes are primarily about the lives, loves, hardships and hopes of African-Americans.
Slowly the blues spread into urban areas which was mainly due to the fact that many rural blues musicians were leaving the countryside to find work in the factories of major cities. By 1920, three major formats of blues were common: The 8 bar blues, the 12 bar blues and the 16 bar blues. Blues also developed various styles, or subgenres, such as Mississippi Delta blues and Chicago electric blues.
Blues leads are played relying heavily on the notes of a minor pentatonic scale. The minor pentatonic scale played over major chords creates the baseline for the dissonances that drive blues to a resolution. The flatted seventh degree of the minor pentatonic lines up with the flatted seventh in the V7/IV chord which ties the chord progression and the leads together.
Since the chord progression being played are mostly made up of major chords though, degrees from the major scale may also be included when playing blues leads. The major third and major sixth are often added to the minor pentatonic scale to further tie the leads and chords together.
The major third is most often played in blues immediately after the minor third and it often precedes either a resolution to the tonic of the scale or a jump up to the fifth degree.
The major sixth is most often played immediately after the fifth degree of the scale and often precedes a resolution to the tonic of the scale or a jump to the minor third. The tritone jump from major sixth to minor third is commonly played over the IV chord because it outlines the dominant seventh chord played based on that degree of the scale (V7/VII).
The second and minor sixth degrees of the scale may only be played in a context where they are part of a chromatic run at least three notes long, for example: the motion from second - minor third - major third, or the motion from fifth - minor sixth - major sixth.
Another common note present in the blues scale is the flatted fifth or tritone of the tonic of the scale. The most common idea of a blues scale, and the quickest and easiest to pick up consists of a minor pentatonic scale with the added flatted fifth because use of the flatted fifth does not depend heavily on context and may be relied upon almost as frequently as any of the other notes in the pentatonic scale.
The real blues scale includes all the chromatic notes between octaves except for the major seventh and minor second in the following order of commonality of use: tonic, minor third, perfect fifth, minor seventh, perfect fourth, major third, tritone, major sixth, minor sixth, major second.
Blues chord progressions are often made up by major chords and dominant seventh chords. In 12 bar blues (explained later), the chord progression follows the most common underlying driving chord progression in western music moving from the tonic (I) to the sub-dominant (IV) to the dominant (V) back to the tonic (I). In blues, the first tonic is often played as a dominant seventh chord written as the V7/IV. This dominant seventh chord departs from the basic major scale by flatting the seventh degree, but it also creates a dissonance which resolves very nicely to the IV chord. The IV chord then resolves up to the V chord weakly which is often played as a V7 chord, crating a dissonance which resolves to the I chord.
The most common chord progression played in blues is the 12 bar blues pattern which follows this general outline:
I | I | I | I IV | IV | I | I V | IV | I | I
This pattern is heavily based on jazz progression and was mainly adopted to create some sense of uniformity among blues songs. In early blues, the verses were not locked in to twelve bars and the only common line between songs was that it tonally moved from the tonic (I) to sub-dominant (IV) to dominant (V) back to tonic (I). The usual chords to meet these purposes weren't even set, for example the dominant was occasionally played as a III chord rooted on the minor third, or just by hitting the minor third and fifth together to create some semblance of resolution when the 1 chord was returned to. Blues verses could range anywhere from around seven bars in length to fifteen. When record companies began to discover blues musicians, they realized this looseness of playing made blues songs less marketable and made it more difficult to bring many blues musicians together to play with each other, so they urged blues musicians to record their songs in uniform sets of twelve bars like jazz musicians did.
The 12 bar blues progression is essentially a more complicated version of a I IV V progression. If you simplify the bars into sets of two by the strong chords in the set, you can begin to see how this tonally makes sense: (I I)(I), (I I)(I), (IV IV)(IV), (I I)(I), (V IV)(V), (I I)(V). The 12 bar blues can be further simplified into three sections the first being the tonic section with four bars of the tonic (I I I I)(I), the second being the sub-dominant section with two bars of the sub-dominant and two bars of the tonic (IV IV I I)(IV), and the third being the dominant section with a bar of the dominant, a bar of the sub-dominant, and two bars of the tonic (V IV I I)(V). The presence of the two bars of tonic in the sub-dominant section doesn't change the tonal feel of the section, but gives it a feeling of motion and interest, just as the presence of the sub-dominant and tonic in the dominant section do. The V IV I return to I also creates a more powerful resolution because the most powerful motions in music are the V - I relationship, and scalar movement. The V to IV creates scalar motion without losing the dominant feel of the first chord then resolves to the I in the same direction of the scalar motion. Since the dominant feel has not been lost, the resolution still feels like it is moving straight from from V to I. Any twelve bar blues song can be played in a simplified version by playing the chord progression:
I | I | I | I IV | IV | IV | IV V | V | I | I
Another common practice in blues is to play the entire song over a single chord, for example, listen to catfish blues, first recorded by Skip James, or I'm a Man by Bo Diddly. The song is often driven by a single riff that adds interest and a backbone behind the lyrics. This practice doesn't warrant too much explanation due to its simplicity.
Common Blues Elements
One of the most recognizable blues riffs is the Mannish Boy riff. This riff is commonly played over a single chord song and creates space between the lines. It can also be heard in Hoochie Coochie Man, and George Thourogood's Bad to The Bone. It is most commonly played in the key of G because in this key it can be played easily on all Bb brass instruments, harmonica, slide guitar in both standard tuning, and open G, piano, and bass. The riff is played: G A G Bb G.
Another common blues practice, especially on electric guitar is the shift from a power chord to the interval on the major sixth and back. This rhythm switching back and forth serves as the backbone of most electric blues and early rock. Over twelve bar blues, this rhythm would be played
|E E E E E E E E E E E E E E E E A A A A A A A A E E E E E E E E B B B B A A A A E E E E E E E E|
|B B C#C#B B C#C#B B C#C#B B C#C#E E F#F#E E F#F#B B D#D#B B D#D#F#F#G#G#E E F#F#B B C#C#B B C#C#|
Finally, the turnaround is a common element of almost every blues song. The turnaround is how blues musicians make transition from the dominant section back to the tonic more interesting. The most simple turnaround is just hitting the V chord at the end of the dominant section again instead of just sitting on the I. The basic concept of most turnarounds is the chromatic run from the minor seventh to the fifth. Many blues musicians abandon the harmonic root of this practice and just play either the notes alone, or some chord containing the minor seventh and chromatically move the chord down four half steps. The chord progression that gave rise to this practice though is V7/IV -> Idim -> IVadd9 -> IIm7b5 -> I.
The lyrics of blues usually takes the form of a narrative. Most blues lyrics deal with personal woes and hard times, or simply day to day life. Blues lyrics rely on the idea that simple and understandable is easier for an audience to relate to than the eloquent and sometimes obscure lyrics in other popular genres of music. Many blues songs also deal with the topics of personal pride, defiance, or powerful emotions other than woe such as love or anger. While blues lyrics seldom turn to extremely happy topics, they are often uplifting, empowering, or humorous. It cannot be said that blues is a 'sad' genre. The blues are a way of dealing with sorrow, rather than wallowing in it.
There are a few main structures of blues lyrics.
Most commonly, a verse over one repetition of a I IV V or twelve bar blues progression consists of two distinct rhyming lines. The first line is repeated twice, first over the tonic section and second over the sub-dominant section. The second line is sung over the dominant section and often sums up the emotion of the first line. A good example of this structure lies in How Many More Years, in which Howlin' Wolf sings:
I "How many more years, do I have to let you dog me around, IV How many more years, do I have to let you dog me around, V I'd rather be dead, lyin' six feet underground"
A second common structure for blues lyrics contains a refrain and a few lines that change in every verse. The progression is played with extra-long measures to accommodate the words. The variable lyrics are sung over the tonic section and the refrain is sung over the sub-dominant and dominant sections. The variable section of lyrics often rhymes with itself and the refrain rhymes with itself, but the rhyme schemes don't carry over between each other. A good example of this structure is the verses of Muddy Waters' song, Can't be Satisfied, in which he sings:
I "Well I'm goin' away to leave, won't be back no more I Goin' back down south, child, don't you want to go? IV Woman I'm troubled, I I be all worried in mind V Well baby I just can't be satisfied I And I just can't keep from cryin'"
A final common structure for blues lyrics is a single line that repeats twice. The first repetition of the line is sung over the tonic chord, and the second is split into two halves, covering the sub-dominant and the dominant chords. A good example of this structure is Robert Johnson's Walking Blues, where he sings:
I "Woke up this morning, looked 'round for my shoes I You know I had those mean old walking blues IV Woke up this morning, I Looked round for my shoes V You know I had those I Mean old walking blues"
For more details on writing a song, go to Writing Effective Songs.