/ˈθɪəri ||; ˈθɪərɪ/noun (
plural theories)
1 [C] an idea or set of ideas that tries to explain sth 理论；学说: the theory about how life on earth began 关于地球上生命起源的理论
2 [U] the general idea or principles of a particular subject 理论；原理: political theory 政治理论the theory and practice of language teaching 语言教学的理论与实践
3 [C] an opinion or a belief that has not been shown to be true 看法；推测；揣度
in theory as a general idea which may not be true in reality 理论上:
Your plan sounds fine in theory, but I don't know if it'll work in practice. 你的计划理论上不错，但我不知道实际上是否可行。