Causality (also referred to as 'causation', or 'cause and effect') is the relation between an event (the cause) and a second event (the effect), where the first event is understood to be responsible for the second.In common usage, causality is also the relation between a set of factors (causes) and a phenomenon (the effect). Anything that affects an effect is a factor of that effect. A direct factor is a factor that affects an effect directly, that is, without any intervening factors.