Hiromi asked:

What is the categorical imperative? Why, according to the categorical imperative, is it immoral to
make a false promise?

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The categorical imperative is stated as "Act only on that maxim whereby you can at the same time will
that it should become a universal law". This is an objective duty, valid for all rational beings, stating
how they oughtto act. It is contrasted with a hypothetical imperative which is conditional upon such
things, as "if you want to look kind..." or "if you want to avoid reproach..." etc. It is a formal principle
and doesn't prescribe any particular actions. It is often formulated along the lines of "Treat others as
they would treat you" and has application to any particular action with regard to others, as well as to
the self. Suicide is immoral because we cannot will that suicide become a universal law.

We cannot will as a universal law that promises should be broken because we cannot lie and at the
same time will that everyone makes deceitful promises, as it is a contradiction. If all promises were
deceitful, we could not even promise. Otherwise put, we would not have others break their promises
to us. To break a promise is to act upon a hypothetical imperative: "If I want to extricate myself from
my present difficulties then...". Kant suggests that a "greater inconvenience" may come from breaking
a promise on this basis because we cannot see the consequences, so it is not even prudent. But lying
or promise breaking is not wrong just because the consequences could lead to greater evil. It is
categorically prohibited, or against the moral law as stated by the categorical imperative. One should
not ask oneself what advantage a false promise would bring to oneself. One should ask "is it right" or
"could I will that anyone can make a false promise if it is to his personal advantage?"

The moral law also prescribes that we treat all human beings similarly "as an end": When we act
upon a hypothetical imperative we might use a person as a means to an end, and an example is
making a false promise. To use someone for one's own purposes is to use him as a means and this,
too, violates the categorical imperative. We cannot will that it is a universal law that everyone should
use another person as a means to an end, or for one's personal advantage.

Rachel Browne