I will outline a formal semantic theory of causal claims, and discuss some of the ways in which it differs from past and present alternatives. Features discussed will include: the primitive structure on which to define truth conditions of causal claims; the absence of detailed accounts of the logical role of background conditions in most alternative theories; and using propositions as causal terms vs. giving some ontological account of causes. I will not attempt to present a complete set of necessary conditions on causal claims, but just the subset of these that relate to nomic dependencies, and suggest that the role that causes play in explanation reasonably introduces further pragmatic and contextual conditions. So, the theory will, at best, include those conditions that establish the appropriate kind of nomic relation that exists between cause, effect, and background conditions, and, tentatively, the direction of causation.