principle
1.原则;原理[C]
I take this seriously. It's a matter of principle.
我对此很认真。这是原则问题。
2.主义;信条[C]
3.(机器等的)原理;构造;工作方式[C]
The two machines work on the same principle.
这两部机器的工作原理是一样的。
4.道义,节操[U]
He is a man of high principle.
他是节操高尚的人。
5.起源,本源
theory
1.学说;论说;...论[C][(+of)][+that]
Darwin spent more than twenty years working on his theory of evolution.
达尔文花了二十余年时间研究他的进化论。
2.理论;学理,原理[U][C]
It seems good in theory, but it doesn't work in practice.
理论上它似乎很不错,但实际上却行不通。
3.意见;推测,揣度[C][+that]
My theory is that we'll have a cold winter this year.
依我看今年冬天会很冷。
Many scientists accept the theory that the universe is growing larger.
许多科学家接受这样的看法:宇宙在不断增大。
简单说
principle强调准则、原则
theory 强调理论 ,与实践相对 apply theory to practice 把理论应用于实践