theory
/ˈθɪərɪ/noun
(pl.-ies)
1- a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained学说; 论说; 论, 说：
Darwin's theory of evolution.
达尔文的进化论。
1.1
- a set of principles on which the practice of an activity is based理论; 学理, 原理：
a theory of education
教育理论
mass noun music theory.音乐原理。
1.2
- an idea used to account for a situation or justify a course of action意见, 看法; 推测：
my theory would be that the place has been seriously mismanaged.
依我看这个地方的管理十分混乱。
1.3
- Mathematics a collection of propositions to illustrate the principles of a subject【数】论, 理论。
短语
in theory
- used in describing what is supposed to happen or be possible, usually with the implication that it does not in fact happen理论上（应该）; 照道理：
in theory, things can only get better; in practice, they may well become a lot worse.
理论上情况只会变好, 实际上却很可能变得更糟。
词源
late 16th cent. (denoting a mental scheme of something to be done)： via late Latin from Greek theōria 'contemplation， speculation'， from theōros 'spectator'.