About Improvisation
Under each song and rhythm pattern are printed the letter names of the chords that can be used to accompany that piece. These particular chords are used because the notes of the song or the rhythm pattern fit in well with the notes of the chord.
When a harmonica player is playing a particular song, especially one that he or she knows well, the notes of the song are of primary importance, for it is the specific arrangement of the notes that makes a song recognizable. Although playing along to a guitar or keyboard chord accompaniment may make for a richer, fuller sound, it is not necessary.
Some types of music are not so much based on a specific arrangement of notes (which is called a "melody", or "tune"). Instead, styles of music such as blues, and the jazz and rock styles that come from the blues, are often "improvised".
Improvisation is the act of creating music as it is being played. Unlike playing a specific song with its specified notes, this way of playing offers the blues musician a great deal of freedom in choosing the notes. However, the notes used in blues improvisation are far from randomly chosen — rather, they are most often chosen largely from the Blues Scale, as explained in later lessons.
In order to give themselves a certain degree of order or organization, improvising musicians often play along with an accompaniment of chords. Thus they have a structure upon which to base their improvisations, and often allow their choice of notes to be determined by their knowledge of which notes will fit in well with those chords.
About Chord Structures
A "chord structure", also known as a "chord progression", is any particular sequence of chords that form one verse of a song.
For example, the chord structure of the song Oh When The Saints Go Marching In might be described as a C to G to C to F to C to G to C structure. You may wish to verify this by looking at the letter names of the chords, which are written below the harmonica notation for each line of the song. This might also be written as a C-G-C-F-C-G-C structure. Each verse of the song uses these same three chords, C, F, and G, in the same order.
Certain chord structures are especially popular for improvising musicians to use. Learning to play some of these popular chord structures in a very simplified way will prepare you for improvising blues, rock, and jazz music. In fact, once you have memorized a chord structure, you will be able to improvise along with your memory of that chord structure, even though you do not have a guitarist, keyboard player, or full orchestra to provide it in real life.
About The Twelve Bar Chord Structure
Most blues and many rock styles of music are heavily based on a particular repeated series of chords called "The Twelve Bar Chord Structure", as is a great deal of jazz.
Literally thousands of well known blues, rock, and jazz songs utilize The Twelve Bar Chord Structure, also known as the Twelve Bar Progression or the Twelve Bar Blues Structure, which you will play in a moment.
The Twelve Bar Chord Structure can be played in any key. The key that it is played in will determine the chords that are used. The Appendix on page 100 will list the chords used to form a Twelve Bar Chord Structure in each key.
Playing The C Harmonica In The Key Of G: "Second Position" Harmonica, Or "Cross Harp"
It might seem obvious that music in the key of C would be easiest to play on a C harmonica. And non-blues songs, like Jingle Bells and Oh When The Saints Go Marching In can be most simply played in the same key as the key of the harmonica.
Your C harmonica will play this type of song in C quite naturally, as you know if you have used the Progressive Harmonica Method prior to approaching the blues with this book. This is because most non-blues songs are based on a particular sequence of notes known as the Major Scale. To learn a little more about the Major Scale if you are so inclined, please turn to page 96 of the Appendices.
But it is easiest to play blues on the C harmonica in the key of G, although other key blues are possible for the advanced player. This is due to the fact that the C harmonica can most easily produce a Blues Scale in the key of G. This will be discussed further in Lesson Twenty One, when the Blues Scale is covered.
Playing in the key of G on a C harmonica is known as playing "second position" harmonica, or "cross harp". When playing cross harp, the key of the harmonica is always four whole steps above the key of the blues, which you can easily verify for yourself by counting the notes from G (1) to A (2) to B (3) to C (4). Following is a chart describing which key harmonica must be used to play cross harp, or second position blues, in any key. As you can see, your C harp will play cross position blues in the key of G. If sharp (#) and flat (b) signs confuse you, please see page 97.
Second Position or Cross Harmonica Chart
The Repeat Sign
The repeat sign: 
tells the reader to repeat the entire piece preceding it. When used at the end of a song, repeat the entire song. When used at the end of a line that is not at the end of a song, repeat only the line preceding the repeat sign. This useful sign will be used throughout the book.
