I think we should go back to first principles.

我认为我们应该回到基本原则上。

One of the first principles of probability theory is called the multiplication rule.

概率论的基本原理之一叫做乘法法则。

You start from first principles.

你要从一系列最初的原则开始。

Let's start with first principles.

让我们先从原理开始。

We must come back to first principles.

作“原理，原则”讲时，是可数名词。