The general form of a decision-making model raises hypotheses about the dynamics of stimulus, conception, and response. One might suppose that the decision progress begins with the perception of some sort of stimulus. The amount of information available for decision-making is often incomplete and hence any logic that attempts to model decision-making must be nonmonotonic in nature. The existing logics can handle defeasible nonmonotonic inferences. The authors propose a modified first-order logic so that defeasible beliefs can also be handled. The modification is in the form of a set of proper axioms to handle belief revision, and a modified modus ponens to capture nonmonotonic reasoning. The proposed logic is extended to model decision-making activity. >