Germaine to what Marje posted just above, I've had occasion to talk with Richard Dyer-Bennet a couple of times. I once asked him how many songs he estimated that he knew, and he responded, "About 700."

That dwarfed my repertoire at the time of about 200 songs, so I asked him, "How do you manage to keep them all fresh? Or do you?"

He said, "I regularly sing about 50 concerts a year. Some performers will sing the same songs at every concert when they're on tour, but when I did that, I found I was forgetting some of my other songs. So now I try to go through an entire concert tour singing different songs at each concert—not repeating a song until I've gone through them all. That tends to keep them fresh in my mind."

Some people don't like Richard Dyer-Bennet because of his high, light tenor voice and his cultivated, carefully studied delivery. But he was the consummate concert performer, and not so much a "folk singer" as a modern counterpart of a medieval minstrel. He didn't just learn a song, he would study it carefully, and learn as much as he could about its historical background.

There's an important difference between just learning the words of a song and knowing a song. Dyer-Bennet advocated the latter.

We only had a couple of fairly brief conversations, but I learned a great deal from him.

Excellent biography of Richard Dyer-Bennet:   

Richard Dyer-Bennet:   The Last Minstrel, by Paul O. Jenkins.

Don Firth