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

馬克思創立了一種新理論，認爲歷史的演變是基於對立集團之間的沖突之上的。

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

愛因斯坦於 1905 年創立了相對論。

There was a theory that he wanted to marry her.

有人認爲他想娶她。

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

我對離婚的看法是，傷害孩子的不是婚姻的破裂，而是處理離婚的方式。

He taught us music theory.

他教我們樂理。

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

在統計學理論和實踐兩方面都訓練有素的畢業生

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

照理說，學校也有牙醫診所，可實際上，裏面的牙醫寥寥無幾。