Hi, This is a very good question. There are two issues in your letter. The first is about matching a melody to an existing chord and the second is actually about what we call - a slash chord.
I'll begin with the slash chord. When you take the C chord(C E G) and you play it together with a low F note you get a slash chord (CEG/F). The concept here is matching a chord with a bass note. Click here to read more about slash chords.
Your first question is actually a bit more complicated. It is about matching a melody to the harmony. For example when you play the C chord, you could play various notes above it. The C E and G will sound good together with the C chord. On the other hand F, B and other notes will not sound good with this chord. There is a reason for that which comes from physics laws.
However, we do encounter in many cases the combination of F with the C chord. Usually in these cases the F is not accented as it doesn't come on a strong beat, or if you play the melody GFE while playing the C chord, the F sounds ok.
I have just mentioned some of the harmony and voice leading laws which explain the relationship between the melody and the harmony. Actually there are many more laws for this and there are full books which explain this field of music.
At this stage I would recommend you to develop your musical hearing. The best law for matching melody to a harmony is - "does it sound good?" Play and listen.
There is a full course by Hear and Play which will help you to develop essential music skills. After this course you will feel much better the relationship between the melody and the harmony. Click here to learn more about Hear and Play.
I hope that I have helped you. Please don't hesitate to ask us further questions.
Ido from www.piano-play-it.com
Fitting Chords to a melody by: Angel Shadowsong Warren
Hi Que,
To match chords, with the chord C and a melody F, you may want to try a Csus4 chord Instead of C/F
That is C-F-G.
However, you must rate the F note if it is a strong note or just a passing note.
Strong notes are measured as quarter note to whole note(inside a bar).
It depends on the Progression however, if your composition is like
C-E-F-G-E, where F is in between E and G and F measures less than a quarter note then it is most probably a passing note.
If it is a passing note you may need not to change a chord as the F will go and lead to G when G is a C major chord.
A slash chord has a use on its base to direct that the progression leads to a note that contains F.
Example if your chord is C and it will go to F or Dm or B diminished, you may use C/F as a C-E-G sounds FAR TO D-F-A and B-D-F compare to F-A-C