A classic, one of the most insightful things ever written about programming, and way ahead of its time (1985).
The actual paper is at http://alistair.cockburn.us/ASD+book+extract%3A+%22Naur,+Ehn... (Edit: that link is broken now, but http://pages.cs.wisc.edu/~remzi/Naur.pdf still works.)
What Naur means by "theory" is some combination of what we'd now call "model" and "design".
Naur put the N in BNF and played a role in creating Algol.