Model-based revision of knowledge bases ex­ pressed as first-order theories was shown in [Winslett 88b] to be useful as a means of de­ scribing and reasoning about the effects of ac­ tions. This paper shows that model-based the­ ory revision is actually expressible as a form of circumscription. This shows that in cer­ tain applications, the cumbersome conceptu­ ally machinery of circumscription...