There's a version of "The Braes of Yarrow" that I sing in the key of Am, and at one point in each verse, I hit a Maj 7th (F-A-C-E, with the E on top) and linger on it for a second or two. Perfect at that point in the verse. Resolves back to the Am. A regular F major at that point sounds too major, but the F major 7th works if I hold it for a second, then end the verse on the Am.

But I'm not using a particular picking or strumming pattern. I'm playing the chords "freely," with occasional arpeggios and runs.

Don Firth