Excerpt from his upcoming Memoir, Unknown Pleasures (to be released later this month), in the NYT Magazine:

That was the thing about Joy Division, though: writing the songs was dead easy because the group was really balanced. We had a great guitarist, a great drummer, a great bass player and a great singer. Ian would listen to us jamming and then direct the song until it was . . . a song. He stood there like a conductor and picked out the best bits. Which was why, when he killed himself a year later, it made everything so difficult. It was like driving a great car that had only three wheels. The loss of Ian opened up a hole in us, and we had to learn to write in a different way. We were so tight, as a group, we didn’t even use a tape recorder half the time. Didn’t need one.

This makes it all the more impressive that the group went on after Ian.