I remember hearing people (jazzers) talk about chord substitutions. I recall hearing about using "tritone substitutions" which I can only assume means something like playing the same type of chord (Min, Maj, Dom, etc) a tritone away from the chord you're on....so, for example, playing an F# minor where you'd normally have a C Minor. It generally sounds bad/odd to do this but I assume I'm missing something or other. Maybe they're just used as a "passing chord/tone" on the way to another chord (like on the and of four, before the change??), or, maybe there's a more accurate and better sounding way to utilize such weirdness.....anyone know anything about this idea??