Scientists and science enthusiasts can get exasperated by the conflation of definitions between the scientific conception of a theory and the colloquial definition. In the latter, a theory is sometimes considered no better than a guess, and at best what a scientist would call a hypothesis (an educated formulation of a mechanism or explanation). People will say things like “evolution is just a theory” as if that attests to some shortcoming of evolution. In the scientific conception, a theory is the gold standard. It is a set of inferences, explanations, predictions, and interpretations that bring together (sometimes disparate) data, evidence, and observations into a cohesive whole. Theories are what scientists use to make predictions in order to formulate new hypotheses and design new experiments. But what is the nature of a theory? And what is the ontological status of a scientific theory? In what way is a theory true?