Harold Kelley's covariation principle is a central model within attribution theory, an area of social psychology that is concerned with the scientific analysis of the psychology of everyday people. Attribution theory was originally introduced by Fritz Heider in 1958 and assumes that we all want to understand and explain events. For instance, we ask why we succeeded at a task or why our friend liked a movie. The answers to such “why questions” (e.g., “I am smart” or “The movie was good”) are called causal attributions. Kelley's model explains how laypersons arrive at such attributions; hence, it is a scientific theory about naive theories.

For both scientists and laypersons, explanations consist of effects to be explained (e.g., success at a task or liking a movie) and ...