Marx produced a new theory about historical change based upon conflict between competing groups.

马克思创立了一种新理论，认为历史的演变是基于对立集团之间的冲突之上的。

Einstein formulated the Theory of Relativity in 1905. [+ of]

爱因斯坦于 1905 年创立了相对论。

There was a theory that he wanted to marry her.

有人认为他想娶她。

My theory about divorce is that it's not the split-up that damages children, it's how it is handled.

我对离婚的看法是，伤害孩子的不是婚姻的破裂，而是处理离婚的方式。

He taught us music theory.

他教我们乐理。

...graduates who are well-trained in both the theory and practice of statistics.

在统计学理论和实践两方面都训练有素的毕业生

A school dental service exists in theory, but in practice, there are few dentists to work in them.

照理说，学校也有牙医诊所，可实际上，里面的牙医寥寥无几。