There is only one categorical imperative...

There is, therefore, only one categorical imperative.  It is: Act only according to that maxim by which you can at the same time will that it should become a universal law.


Now if all imperatives of duty can be derived from this one mperative as a principle, we can at least show what we understand by the concept of duty and what it means, even 
though it remain undecided whether that which is called duty is 
an empty concept or not.


The universality of law according to which effects are produced constitutes what is properly called nature in the most general sense (as to form), i.e., the existence of things so far as it is determined by universal laws. [By analogy], then, the universal imperative of duty can be expressed as follows: Act as though the maxim of your action were by your will to become a universal law of nature.

Would robots have any difficulty with categorical imperatives?

We shall now enumerate some duties, adopting the usual division of them into duties to 
ourselves and to others and into perfect and imperfect duties.


1. A man who is reduced to despair by a series of evils feels a weariness with life but is still in possession of his reason sufficiently to ask whether it would not be contrary to his duty to himself to take his own life.  Now he asks whether the maxim of his action could become a universal law of nature.  His maxim, however, is: For love of myself, I make it my principle to shorten my life when by a longer duration it threatens more evil than satisfaction. But it is questionable whether this principle of self-love could become a universal law of nature.  One immediately sees a contradiction in a system of nature whose law would be to destroy life by the feeling whose special office is to impel the improvement of life.  In this case it would not exist as nature; hence that maxim cannot obtain as a law of nature, and thus it wholly contradicts the supreme principle of all duty.


2. Another man finds himself forced by need to borrow money.  He well knows that he will not be able to repay it, but he also sees that nothing will be loaned him if he does not firmly promise to repay it at a certain time.  He desires to make such a promise, but he has enough conscience to ask himself whether it is not improper and opposed to dutty to relieve his distress in such a way.  Now, assuming he does decide to do so, the maxim of his action would be as follows: When I believe myself to be in need of money, I will borrow money and promise to repay it, although I know I shall never do so. Now this principle of self-love or of his own benefit may very well be compatible with his whole future welfare, but the question is whether it is right. He changes the pretension of self-love into a universal law and then puts the question: How would it be if my maxim became a universal law? He immediately sees that it could never hold as a universal law of nature and be consistent with itself; rather it must necessarily contradict itself.  For the universality of a law which says that anyone who believes himself to be in need could promise what he pleased with the intention of not fulfilling it would 
make the promise itself and the end to be accomplished by it impossible; no one would believe what was promised to him but would only laugh at any such assertion as vain pretense.


3. A third finds in himself a talent which could, by means of some cultivation, make him in many respects a useful man.  But he finds himself in comfortable circumstances and prefers indulgence in pleasure to troubling himself with broadening and improving his fortunate natural gifts.  Now, however, let him ask whether his maxim of neglecting his gifts, besides agreeing with his propensity to idle amusement, agrees also with what is called duty. He sees that a system of nature could indeed exist in accordance with such a law, even though man (like the inhabitants of the South Sea Islands) should let his talents rust and resolve to devote his life to idleness, indulgence, and propagation—in a word, to pleasure.  But he cannot possibly will that this should become a universal law of nature or that it should be implanted in us by a natural instinct. For, as a rational being, he necessarily wills that all his faculties should be developed, inasmuch as they are given to him for all sorts of possible purposes.


4. A fourth man, for whom things are going well, sees that others (whom he could help) have to struggle with great hardships, and he asks, “What concern of mine is it? Let each one be as happy as heaven wills, or as he can make himself; I will not take anything from him or even envy him; but to his welfare or to his assistance in time of need I have no desire to contribute.” If such a way of thinking were a universal law of nature, certainly the human race could exist, and without doubt even better than in a state where everyone talks of sympathy and good will or even exerts himself occasionally to practice them while, on the other hand, he cheats when he can and betrays or otherwise violates the rights of man.  Now although it is possible that a universal law of nature according to that maxim could exist, it is nevertheless impossible to will that such a principle should hold everywhere as a law of nature.  For a will which resolved this would conflict with itself, since instances can often arise in which he would need the love and sympathy of others, and in which he would have robbed himself, by such a law of nature springing from his own will, of all hope of the aid he desires.


The foregoing are a few of the many actual duties, or at least of duties we hold to be actual, whose derivation from the one stated principle is clear. We must be able to will that a maxim of our action become a universal law; this is the canon of the moral estimation of our action generally.  Some actions are of such a nature that their maxim cannot even be thought as a universal law of nature without contradiction, far from it being possible that one could will that it should be such. In others this internal impossibility is not found, though it is still impossible to will that their maxim should be raised to the universality of a law of nature, because such a will would contradict itself. We easily see that the former maxim conflicts with the stricter or narrower (imprescriptible) duty, the latter with broader (meritorious) duty.  Thus all duties, so 
far as the kind of obligation (not the object of their action) is concerned, have been completely exhibited by these examples in their dependence on the one principle.