Michael asked:

Why are maxims or principles important for Kant's ethics?

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Principles are important because Kant wants to explain and ground our sense of morality, which he
takes as acting on obligation rather than impulse. Impulse doesn't have moral import. Kant thought
that we actually do act from a sense of duty to others. If we act according to a sense of duty, we act
on principles which can be worded in the form that we "ought" to do such and such. Before Kant,
Hume said that we can't derive an "ought" from an "is" and if Hume is right and there is no ground for
recognising an "ought" there is no obligation and acting from moral duty doesn't make sense. But, as
Kant recognised, we do act from a sense of obligation. Kant thought this was the essence of moral
action.

In acting on principle we are not acting on impulse or motivated by mere desire. We are rational and
can act contrary to desire. However, there are two senses of principles and maxims. To motivate us
our principles or maxims must be subjective — or ones we are committed to. To be moral these
maxims we are committed to must be universalisable and essentially universalisable by ourselves as
individuals. If we merely acted from desire, we couldn't produce reasons (in terms of maxims and
principles) but as rational beings we can be committed to principled action and perform such actions
even when we don't actually want to do so. As free rational beings we can commit ourselves to a
principle or maxim.

Rachel Browne