The purpose of this note is to draw attention to certain aspects of causal reasoning which are pervasive in ordinary discourse yet, based on the author’s scan of the literature, have not received due treatment by logical formalisms of common-sense reasoning. In a nutshell, it appears that almost every default rule falls into one of two categories: expectation-evoking or explanation-evoking. The former describes association among events in the outside world (e.g., Fire is typically accompanied by smoke.); the latter describes how we reason about the world (e.g., Smoke normally suggests fire.). This distinction is consistently recognized by people and serves as a tool for controlling the invocation of new default rules. This note questions the ability of formal systems to reflect common-sense inferences without acknowledging such distinction and outlines a way in which the flow of causation can be summoned within the formal framework of default logic.