theory/ˋθiərI; ˈθIəri/n plural theories 1 [C] an idea that tries to explain something [→ theoretical] 学说﹔理论: +of Darwin's theory of evolution 达尔文的进化论+about different theories about how the brain works 关于大脑如何运作的各种学说One theory is that he was killed by members of a rival gang. 一种观点认为他是被敌对团伙的成员杀死的。2 in theory something that is true in theory should be true, but may not actually be true 理论上﹐从理论上来说〔实际上未必如此〕: In theory, I don’t work on Saturdays. 理论上来讲﹐我星期六不工作。3 [U] the general principles of a subject〔某一学科的〕理论﹔原理: studying economic theory 学习经济学理论