In Linguistic, the causal is a Cas expressing the reason or the reason for the action expressed by the principal verb. The opposite says Effectual.

Treatment of the signals

In Digital processing of the signal, a causal signal is defined by:

$s\; (T)\; =0$ for

A signal is known as causal if this signal is null when t<0

By opposition, a not-causal signal east defines on the whole of realities. The signal exists even if t<0.