PRUDENCE AND DUTY V
Kant takes the above test cases to show “that if duty is a conception which is to have any import and real legislative authority for our actions, it can only be expressed in categorical, and not at all in hypothetical imperatives.”
Thus one does not say, if you want to be well-liked, then help others in need, which is a hypothetical imperative which might be thought prudent for a person to follow. Instead, we see that we ought to help others since a principle which maintains that we ought not to help others in need cannot be consistently universalized.
Helping others then fits the categorical imperative which pertains to the universalization of correct moral actions.