nickmaynard wrote:can you share examples?
Try this. Play a D minor chord. D minor basic triad is D - F - A. The corresponding minor harmonic scale is D E F G A Bb C# D. As an experiment , play a sucesion of notes over D minor, and one of the notes will be G#, which does not belong neither to the chord, neither to the scale.
Play in eights over the Dm chord in 4/4, the following notes G# A C D C A C D (Being G# the lowest of them).
Now play A G# A C D C A C. This time the G# will tend to sound more integrated to the musical idea than in the first case (always depending on the way that you play it... we are talking about volume, accent, attack...) This is because the note outside the scale is played on the upbeat. Now, play A C A G# A C D C. This time the G# blends really well, as it is on the upbeat of the second beat which is supposed to be a weak one. Having this in mind, you may decide when you want the "outside" note to be more shocking or when you want it to be more subtle. It will depend of the idea you are trying to transmit as composer, at that particular moment.
Take a look at a couple of popular songs. "All Shook Up" by Elvis Presley, at the second bar, over a Bb chord the melody goes for a brief moment to C# (in the downbeat of the second beat), because of its position it blends perfectly with the rest of the melody.
Another example, the jazz standard "Angel Eyes", in the first bar (Second beat upbeat) it has an Ab over a Dm6 chord, which is an outside note, but this note lasts to the next beat and the chord changes to a Bb9 chord becoming an inside note of the second chord as it is the minor sevenths of Bb.
You´ll find several examples looking in tunes here and there. Certainly, as it was suggested, pay attention to Bach, we could say that the man invented the rules and broke them better than anyone. I think it could be a good excersize, analizing his music with the partitures.
In jazz there are lots of cases of playing outside the harmony from subtle elegant ways, such as Duke Ellington to totally avant garde expresions like Sun Ra.
Hope this can help.