The primary rules of obligation are those that require or forbid certain actions.

I have always been a stranger in this world, a visitor, a tourist.

The past is always with us, for it feeds the present.

对付不自由世界的唯一方法就是变得如此绝对自由，以至于你的存在本身就是一种反叛。

The principles of conditioning apply equally to all species.