Process cause or mechanism that explains how a pattern occurred (why/how); not observable. Easier to document patterns than to understand processes. Since most processes are not observable, we build models to figure out what"s going/ to test hypotheses. Models simplified imitations of reality built using observation and inference: theoretical, similar to an analogy, ex. Electrical current flows like a river : ex. Evolutionary tree : quantitative representations of a system using numerical representations, ex. Computer simulations: something you can touch, ex. Problems with models: confuse the real with the model, limit further testing because of already set idea. Good models: account for all known, correctly predict, consistent. Supernatural explanations can"t be tested so they"re not a part of science. Theory how or why it happens . Not just a tentative explanations; they are well-substantiated explanations that incorporate facts, inferences and tested hypotheses. Physical: association study, natural experiment, thought experiment, causation experiment.