| 1. | a coherent group of general propositions used as principles of explanation for a class of phenomena: Einstein's theory of relativity. |
| 2. | a proposed explanation whose status is still conjectural, in contrast to well-established propositions that are regarded as reporting matters of actual fact. |
| 3. | Mathematics. a body of principles, theorems, or the like, belonging to one subject: number theory. |
| 4. | the branch of a science or art that deals with its principles or methods, as distinguished from its practice: music theory. |
| 5. | a particular conception or view of something to be done or of the method of doing it; a system of rules or principles. |
| 6. | contemplation or speculation. |
| 7. | guess or conjecture. |

In science, an explanation or model that covers a substantial group of occurrences in nature and has been confirmed by a substantial number of experiments and observations. A theory is more general and better verified than a hypothesis. (See Big Bang theory, evolution, and relativity.)
theory the·o·ry (thē'ə-rē, thēr'ē)
n.
A systematically organized body of knowledge applicable in a relatively wide variety of circumstances, especially a system of assumptions, accepted principles, and rules of procedure devised to analyze, predict, or otherwise explain the nature or behavior of a specified set of phenomena.
Abstract reasoning; speculation.
| theory (thē'ə-rē, thîr'ē) Pronunciation Key
A set of statements or principles devised to explain a group of facts or phenomena. Most theories that are accepted by scientists have been repeatedly tested by experiments and can be used to make predictions about natural phenomena. See Note at hypothesis. |