An examination of the statement, criticism, and reformulation of the Pirenne, Turner, and Weber theses as causal explanations makes possible a clarification of the nature and justification of causal theses in history. Criticisms of such theses typically attack either the description of the cause-phenomenon or the effect-phenomenon, or they attack the (sometimes implicit) generalization or theory which justifies the claim of causal connection. Theses are defended by redescribing the phenomena so as to make the underlying theory (e.g., the psychological mechanisms postulated by Turner and Weber) a stronger justification. The analysis clarifies the essential connection between description and explanation, and shows that "colligatory" descriptions are always theoretical relative to lower-level factual descriptions.