In classical style brief definitions would be...
Dominant: a major chord, built on the tone a perfect fifth above the tonic, used to form authentic, half, and deceptive cadences.
Plagal: a cadence type (disputed by some) moving from a chord without the leading tone to the tonic chord.
Can someone offer brief descriptions for the meanings in medieval music? Of course, more than a sentence is fine. I just would like something concise.
My current understanding is 'dominant' is a tone other than the tonic that the melody tends to center around. I'm not sure I really understand how that dominant would really be treated. In E Phrygian C is the dominant. Won't centering around that start to sound (perhaps only to modern ears) like C major?
Plagal is the form of the scale where the tonic is placed in the middle of the ambitus (?) a 4th above lowest tone and a 5th below the highest tone. When a plagal scale was used did the melody actually confined to that ambitus? Like is D Hypodorian were the
A's the lowest and highest tones.