noun, plural: theories
(2) An expectation of what would happen, excluding unforeseen circumstances. For instance, the theory that criminals usually return to the scene of the crime.
(science) A set of statements or principles that may be tested through experimentation or otherwise by reasoning to explain certain facts or phenomena, and thereupon may be used as basis for predicting similar future occurrences or observations.
The common use of the term theory implies speculation or assumption that has not been verified or has limited proofs. However, in science, a theory is a well-substantiated explanation or a set of statements that have been confirmed over the course of many independent experiments. In comparison, theories are more certain than hypotheses but less certain than laws. And in science, an unproved idea or a mere theoretical speculation is regarded as a hypothesis rather than a scientific theory.
Word origin: L theōria < Gk theōría a viewing, contemplating.