Sorry I meant to add that a good example of a melodic minor mode is the Nursery Rhyme Higgledy Piggledy my black hen. The second cadence goes straight down the scale. Or if you prefer the last line of Bert Lloyds Trim Rigged Doxy. Either way 'God rest ye merry, gentlemen' is a magnificent tune. Ken Loveless used to be very insistent about the pause between 'merry. and 'gentlemen'. i.e. 'Be happy Gentlemen there is good news. Here endeth the lesson you'll be relieved to know.