The cause which owes its existence to the “causa causans”; the secondary cause. The vera causa is (a) the immediate predecessor of an effect; (b) a cause verifiable by independent evidence. (Mill.)
In theology God is the causa causans, and creation the causa causata. The presence of the sun above the horizon is the vera causa of daylight, and his withdrawal below the horizon is the vera causa of night.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894