Theory :  (noun)
1: a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"
2: a tentative theory about the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena; "a scientific hypothesis that survives ... ( more )

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apprehension, assumption, attitude, base, basis, body of theory, climate of opinion, common belief, community sentiment, conceit, concept, conception, conclusion, conjecture, consensus gentium, consideration, estimate, estimation, ethos, explanation, eye, fancy, feeling, general belief, grounds, guess, guesswork, harmonics, harmony, hunch, hypothesis, idea, image, imago, impression, intellectual object, judgment, lights, melodics, memory-trace, mental image, mental impression, mind, music, music theory, musicality, musicography, musicology, mystique, notion, observation, opinion, perception, perhaps, personal judgment, point of view, popular belief, position, posture, premise, presentiment, presumption, prevailing belief, public belief, public opinion, reaction, recept, reflection, representation, rhythmics, sentiment, sight, speculation, stance, supposal, suppose, supposition, surmise, suspicion, tentative explanation, theoretical structure, there, thinking, thither, thitherward, thought, understanding, unified theory, view, way of thinking, yon, yonder,