My (unschooled) understanding of 'modal' was that it refered to songs that have no definable chord progression. That is, a 'G modal tune' is one you that could (as a guitarist) simply strum a G all the way through without it ever sounding wrong. (Not that you'd actually want to do that.) So in modal songs the melody (or mode) is the defining element rather than the chord changes (as it is in blues or country).

I could (however) be utterly wrong here.

B.