The word 作证 is formed through the logical combination of its two component characters: 作, which carries the core meaning "to do, to act, to perform", and 证, which means "evidence, proof, or to prove". They merge not grammatically but conceptually, where the action of 作 is directed toward the object/result of 证, naturally creating the unified meaning "to act as proof" or "to give testimony". It is a direct semantic blend where performing an action related to evidence yields the act of testifying or bearing witness.