Spinoza's Ethics: III.D1: Adequate Cause

Causam adæquatam appello eam cujus effectus potest clare et distincte per eandem percipi. Inadæquatam autem seu partialem illam voco cujus effectus per ipsam solam intelligi nequit.

I name an adequate cause that whose effect is able to be perceived clearly and distinctly. Moreover I call that an inadequate or partial cause whose effect is not able to be understood through itself alone.

Spinoza starts his three book discussion on human affects with causal clarity. He is interested in calling something an adequate cause based on the effect that it generates. This first step is important as his approach is based on many of the human affects being grounded in biases. Adequacy is an attempt to remove biases.