Cross-disciplinary influences
Logic
The research on nonmonotonic logics remains popular (Gabbay et al. (1994b) give an overview) and has broadened its scope to defeasibility (cf. Nute, 1994).
Computer science
The computational complexity of nonmonotonicity attracted the attention of the logic programming community (e.g., Dung, 1993, 1995; Bondarenko et al., 1993).