theory

1. N-VAR A theory is a formal idea or set of ideas that is intended to explain something. 理论

Marx produced a new theory about historical change based upon conflict between competing groups. 马克思提出了一个新理论，认为历史变革是由于对立集团的冲突而产生的。

2. N-COUNT If you have a theory about something, you have your own opinion about it which you cannot prove but which you think is true. 观点

There was a theory that he wanted to marry her. 有种观点认为他想娶她。

3. N-UNCOUNT The theory of a practical subject or skill is the set of rules and principles that form the basis of it. 基础理论

He taught us music theory. 他教我们乐理。

4. PHRASE You use in theory to say that although something is supposed to be true or to happen in the way stated, it may not in fact be true or happen in that way. 从理论上说

Achieving these goals is relatively easy in theory, yet quite difficult in practice. 实现这些目标从理论上说比较容易，但在实践上却相当困难。