theory

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

Marx produced a new theory about historical change based upon conflict between competing groups. 馬尅思提出了一個新理論，認爲歷史變革是由於對立集團的沖突而産生的。

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. 觀點

There was a theory that he wanted to marry her. 有種觀點認爲他想娶她。

3. N-UNCOUNT The theory of a practical subject or skill is the set of rules and principles that form the basis of it. 基礎理論

He taught us music theory. 他教我們樂理。

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. 從理論上說

Achieving these goals is relatively easy in theory, yet quite difficult in practice. 實現這些目標從理論上說比較容易，但在實踐上卻相儅睏難。