Mathematically, congruent means having the same size and shape, being identical in form. The antonyms are incongruent and incongruence. Congruous means to be in agreement or harmony usually in an aesthetic sense. It is rarely used, while its antonym, incongruous, is more common.

In a day to day context, congruence means what a person display outwardly—words, actions, body language, etc.—matches what is on the inside—thoughts, feelings, body sensations, etc. When what is on the outside does not correspond with what is on the inside, one is incongruent.

The conjunction of these features creates trials that are congruent, because both features converge on the same response, or incongruent because they indicate contrary responses.