TESTING MORAL LAWS II
For Kant, a particular moral principle can be tested by asking if a rule pertaining to behavior which goes against the principle can be universalized.
And he says: “If not, then it must be rejected . . . because it cannot enter as a principle into a possible universal legislation” [cannot be a moral law applicable to everyone.]
Thus a test of a maxim or moral law such as ‘keep your promises’ is to ask if a principle pertaining to conduct which would break the law, such as ‘it is okay to make a promise which you don’t intend to keep,’ could be universalized.