·      Here is the chord progression for a simple 8-bar jazz tune:

 | FΔ7 | FΔ7 | C7 | C7 | C7 | C7 | FΔ7 | FΔ7 |...etc

 ·      This gives the player enough information to construct an improvisation.  But how?  What does it all mean?

 ·      In each bar (between one barline, |, and the next) there is a chord symbol.  The chord symbol is a summary of the harmony that applies to that bar.

 ·      The example is the progression of a song in the key of F major.  The two chords that occur in the piece - FΔ7 and C7 - are the most important chords associated with this key.

 ·      How are a key and a chord related?  We can see this if we harmonise the scale.

 ·      In the attached example the scale of F major (F G A Bb C D E F) is given, followed by the same scale but on each degree we show a chord.  The rule for making each chord is to take the scale note, then add the scale note a third above (i.e. if the scale note = 1, add note 3), then the note a third higher again, then a further third higher.

 ·      So on F, the notes are F:A:C:E.  On Bb they are Bb:D:F:A.

 ·      The chord F:A:C is the tonic chord of F major and its symbol is F, or F maj, or F M, or (most commonly these days) FΔ.

 ·      The chord on G (G:Bb:D) has a different makeup from the one on F.  The interval from F to A is a major third.  From G to Bb is a semitone smaller - a minor third.  So the chord on G is G minor, abbreviated G mi or, mostly, G-.

 ·      If F:A:C is FΔ, then the same chord with an E on top (a seventh above the root note F) is called FΔ7.  Similarly G:Bb:D:F is G-7.

 ·      Notice that the chord on C in the scale of F major is C:E:G:Bb.  This is the dominant seventh chord and its symbol is C7.  Don’t confuse it with CΔ7 (which would be C:E:G:B) or C-7 (C:Eb:G:Bb).  These names for the 7^th chords aren’t very logical and there have been attempts to introduce more consistent symbols, but the old system remains the one in widest use - sorry, don’t blame me, I don’t make the rules!

 ·      The chord on E is different again - it has a G (so it’s a kind of E minor) and a D (so it’s a 7^th), but it has a Bb instead of B - a flat fifth.  So it’s E-7 5b, sometimes these days called EØ (half-diminished).

 ·      So the pattern for the chords that harmonise the major scale is:

 IΔ7  II-7  III-7  IVΔ7  V7  VI-7  VIIØ  I¹Δ7...etc

 ·      Examples of four harmonised major scales are shown.  You can work out the patterns for all twelve major keys.  A useful exercise for practice is to play each scale up and down, then play the chord on each scale degree as an up-and-down arpeggio.

 ·      Returning to our simple 8-bar chord progression, we now know that the FΔ7 and C7 chords both occur in the harmonised scale of F major.  This tells us that we can make up an improvised melodic line using notes from the F major scale and these notes will fit correctly with the chords.

 ·      But you may be wondering why, if the same scale fits both chords, there are two chords and not just one, or why these two chords and not any other two from the harmonised F scale?  The answer is that, of course, FΔ7 and C7 have very different harmonic functions, even though they are very close in melodic origin.

 ·      Take a look at the important differences between the two chords.  FΔ7 and C7 share two notes - C and E - but the Bb of C7 makes it quite distinct from FΔ7, whereas the root note of the latter - F - is not strongly implied by the C chord.

 ·      So when improvising on FΔ7, use the scale of F major but don’t emphasise the note Bb, and certainly avoid finishing a phrase on that note.  Against C7, Bb is fine but F becomes a weak note to emphasise.  Notice that Bb, the taboo note for the F chord, is a perfect fourth above F, and that F is likewise a fourth above the root note of C7.

 ·      So a useful rule (by no means unbreakable - just useful) is to be wary of the note a perfect 4^th above the root when improvising on major or dominant seventh chords.  If you’re feeling really adventurous you can use a common modern jazz trick - instead of avoiding the fourth, sharpen it.  More of this anon.

 ·      One last suggestion: even if you are not, and never intend to become, a twinkle-fingered jazz pianist, it is extremely useful for your harmonic sense and improvisation skills to be able to finger chords on the keyboard.  A simple trick is to play just the root note and seventh of each chord (sometimes called the shell) in the left hand and to fill in other notes from the scale with the right.  So for FΔ7, F:E in the left hand is the shell, leaving the right hand to noodle around the scale of F (mind that Bb now!).

 ·      Work out the shells for all the other chords in the harmonised F major scale.