There’s a logic behind every note written in music, & you can learn to understand that logic, and therefore understand music. If you can read music to some degree but don’t “see through” the written music — don’t understand what you are seeing — it is now very possible that you can put on your “chord glasses” that good “chord detectives” wear to see through all that mass of black printed notes on a white page of sheet music to quickly understand what chords are being used and the “family logic” behind it all. The “family logic” is this: In every key there are certain chords which are organic to that key — “family members”, so to speak. For example, in the key of F the 3 most used chords are F, Bb and C. In the key of G the most used chords are G, C, and D. In the key of Eb the most used chords are Eb, Ab, and Bb. Do you see a pattern here?
Article continued at http://playpiano.com/musical-courses/chord-detective.htm