0Accompanying a song melody using chords is perhaps one of the essential aspects of playing guitar..now as we know according to the diatonic harmonisation theory, for any major scale:
1.for scale degrees 1 and 4 the respective Major or Major 7th chords are played.
2.for scale degrees 2,3 and 6 the respective minor or minor 7th chords are played..
3.for the 5th scale degree the respective major or dominant 7th chord is played and
4.finally for the 7th scale degree the respective diminished or minor 7th flat 5th chord is played..the following example will illustrate the theory. let's consider the C major scale..applying the tonal intervallic formula for Any major scale: 1-1-1/2-1-1-1-1/2 we get the notes of C major scale as C-D-E-F-G-A-B-C
SO for
C the 1st scale degree we play the CM7(C+E+G+B)
For D, the 2nd degree we play Dminor 7th or Dm7(D+F+A+C)
For E, the 3rd degree we play Eminor 7th or Em7(E+G+B+D)
For F, the 4th degree we play F Major7th or FM7(F+A+C+E)
For G, the 5th degree we play G dominant 7th or G7(G+B+D+F)
For A, the 6 degrees we play A minor 7th or Am7(A+C+E+G)
For B, the 7th degree we play B minor 7th flat 5th or Bm75b(B+D+F+A)
So practically whenever we play a song based on the C major scale ..we can keep toggling between these family chords depending upon where the melody notes are resting and the chords having that particular note as one of its constituent chord tones can be applied to back up the melody.
This is the basic approach towards harmonising a song melody.But jazz musicians have invented loads of ideas to reharmonizing that makes the songs sound different and harmonically rich and complex. One of the basic ways of reharmonization is the 2-5-1 cadence, i.e., for example, if we are in the key of C major and If in a song we have a C chord followed by an F chord. According to the 2-5-1 approach we shall consider the F chord as the 1(tonic), and before landing on it we shall play the minor chord of F's 2nd degree, i.e., Gm and the 7th chord of F's 5th ,i.e, C7{{This is called a secondary dominant which is often altered by adding a b9,b5 or a #9 or #5 to it, that makes the chord C7b9 or C7 #9 or C7b5 or C7#5 or combinations of both..this adds to the tension that releases once the harmony moves to the 1(tonic )chord}}..so a simple C|F| progression becomes C|Gm C7b9|F.This is an example of a Major 2-5-1 since the 1 chord is a major type chord. Now if the basic progression is a G followed by a Dm chord..here Dm is the 1(tonic) and its a minor type chord ..in this case, the 2 is always an m7b5 (half diminished) chord and the 5th again a 7th chord(often altered to surmount the tension ), so a simple G|Dm| progression becomes G|Em7b5 A7#9| Dm. So I hope this lesson helps you to understand the concepts of a major and a minor 2-5-1 and secondary dominants and altered dominants and most importantly you need to apply this concept to the songs you already know and have fun discovering the fresh reharmonized sound..have fun and stay tuned for more jazz concept lessons from me..!!
