Act only according to that maxim whereby you can at the same time will that it should become a universal law.
Kant concludes that a moral proposition that is true must be one that is not tied to any particular conditions, including the identity and desires of the person making the moral deliberation.
Act as if the maxims of your action were to become through your will a universal law of nature.
In general, perfect duties are those that are blameworthy if not met, as they are a basic required duty for a human being.
Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.
Every rational action must set before itself not only a principle, but also an end. Most ends are of a subjective kind, because they need only be pursued if they are in line with some particular hypothetical imperative that a person may choose to adopt. For an end to be objective, it would be necessary that we categorically pursue it.
The free will is the source of all rational action. But to treat it as a subjective end is to deny the possibility of freedom in general. Because the autonomous will is the one and only source of moral action, it would contradict the first formulation to claim that a person is merely a means to some other end, rather than always an end in themselves.
On this basis, Kant derives the second formulation of the categorical imperative from the first.
The second formulation also leads to the imperfect duty to further the ends of ourselves and others. If any person desires perfection in themselves or others, it would be their moral duty to seek that end for all people equally, so long as that end does not contradict perfect duty.
Thus the third practical principle follows [from the first two] as the ultimate condition of their harmony with practical reason: the idea of the will of every rational being as a universally legislating will.
Act according to maxims of a universally legislating member of a merely possible kingdom of ends.
There is, however, another formulation that has received additional attention as it appears to introduce a social dimension into Kant's thought. This is the formulation of the "Kingdom of Ends."
Because a truly autonomous will would not be subjugated to any interest, it would only be subject to those laws it makes for itself—but it must also regard those laws as if they would be bound to others, or they would not be universalizable, and hence they would not be laws of conduct at all. Thus, Kant presents the notion of the hypothetical Kingdom of Ends of which he suggests all people should consider themselves never solely as means but always as ends.
The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in itself. The theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences.
A man reduced to despair by a series of misfortunes feels sick of life, but is still so far in possession of his reason that he can ask himself whether taking his own life would not be contrary to his duty to himself. Now he asks whether the maxim of his action could become a universal law of nature. But his maxim is this: from self-love I make as my principle to shorten my life when its continued duration threatens more evil than it promises satisfaction. There only remains the question as to whether this principle of self-love can become a universal law of nature. One sees at once that a contradiction in a system of nature whose law would destroy life by means of the very same feeling that acts so as to stimulate the furtherance of life, and hence there could be no existence as a system of nature. Therefore, such a maxim cannot possibly hold as a universal law of nature and is, consequently, wholly opposed to the supreme principle of all duty.
How the Categorical Imperative would apply to suicide from other motivations is unclear.Application of the universalizability principle to the ethics of consumption
Instead of resolving the problems of the poor and thinking of how the world can be different, some can only propose a reduction in the birth rate. ... To blame population growth instead of extreme and selective consumerism on the part of some, is one way of refusing to face the issues. It is an attempt to legitimize the present model of distribution, where a minority believes that it has the right to consume in a way which can never be universalized, since the planet could not even contain the waste products of such consumption.
Kant's objection to the Golden Rule is especially suspect because the categorical imperative (CI) sounds a lot like a paraphrase, or perhaps a close cousin, of the same fundamental idea. In effect, it says that you should act toward others in ways that you would want everyone else to act toward others, yourself included (presumably). Calling it a universal law does not materially improve on the basic concept.
However, deontology also holds not merely the positive form freedom (to set ends freely) but also the negative forms of freedom to that same will (to restrict setting of ends that treat others merely as means, etc.). The deontological system is for Kant argued to be based in a synthetic a priori - since in restricting the will's motive at its root to a purely moral schema consistent its maxims can be held up to the pure moral law as a structure of cognition and therefore the alteration of action accompanying a cultured person to a 'reverence for the law' or 'moral feeling'.
Thus, insofar as individuals freely chosen ends are consistent in a rational Idea of community of interdependent beings also exercising the possibility of their pure moral reason is the egoism self-justified as being what is 'holy' good will because the motive is consistent with what all rational beings who are able to exercise this purely formal reason would see. The full community of other rational members - even if this 'Kingdom of Ends' is not yet actualized and whether or not we ever live to see it - is thus a kind of 'infinite game' that seeks to held in view by all beings able to participate and choose the 'highest use of reason' (see Critique of Pure Reason) which is reason in its pure practical form. That is, morality seen deontologically.
Kant was of the opinion that man is his own law (autonomy)—that is, he binds himself under the law which he himself gives himself. Actually, in a profounder sense, this is how lawlessness or experimentation are established. This is not being rigorously earnest any more than Sancho Panza's self-administered blows to his own bottom were vigorous. ... Now if a man is never even once willing in his lifetime to act so decisively that [a lawgiver] can get hold of him, well, then it happens, then the man is allowed to live on in self-complacent illusion and make-believe and experimentation, but this also means: utterly without grace.