It is a crucial issue for history to determine a cause or a causal relation between two events. The regularity theory of causation is one of the most popular approach to this problem. The paper analyzes mainly how this approach deals with the determination of a causal condition and with the choice of the main cause from the remaining causal conditions. It examines also Mackie’s conception of cause as an INUS condition, which is in fact only one version of the regularity theory. The paper not only outlines and illustrates these approaches, using a concrete causal statments, but also presents the criticism of their shortcomings. It points to their difficulties springing from their inability to distinguish between the laws and accidental generalizations. This is important, because a genuine causal relation cannot be based on the second type of statments.