Situation awareness (SA) is a relatively new concept that has captured the imagination of the human factors community. This new concept is considered in the light of Benton J. Underwood's discussion about psychological concepts. In particular the distinction between SA as a phenomenon description (Level 2 concept) and SA as a causal agent (Level 3 concept) is discussed. The argument that SA is valuable as a phenomenon description draws attention to the intimate interactions between human and environment in determining meaning (or what matters) and reflects an increased appreciation for the intimate coupling between processing stages (e.g., perception, decision, and action) within closed-loop systems. However, I caution against considering SA as a causal agent. When SA is considered to be an object within the cognitive agent, there is a danger of circular reasoning in which SA is presented as the cause of itself. As a causal explanation, SA is a simple, easy-to-understand wrong answer that, in the end, will be an obstacle to research. As a phenomenon description, SA invites further research to discover causal relationships between the design of human-machine systems and the resulting performance.