理论 (lǐ lùn): théorie

He studied theoretical physics at university. Although the courses were difficult, he found exploring the fundamental laws of the universe particularly fascinating.

This paper proposes a new theory that attempts to explain why some animals migrate collectively over long distances.

The coach explained the training theory very clearly, but the players preferred to practice on the field directly, feeling that they would improve faster that way.

When learning a foreign language, grammar theory can help you understand sentence structure, but actually speaking still requires a lot of practice.

Professor Wang has studied economic theory for decades and recently began using these theories to analyze changes in the domestic real estate market.