John Stuart Mill believed in an ethical theory known as utilitarianism and his theory is based on the principle of giving the greatest happiness to greatest number of people, Mill support the pursuit of happiness. On the other hand, Kant who believed in an ethical theory known as Deontologist and he believes that only principle of actions matter and moral decisions should be made based on one duties and right of others.
Utilitarianism believes the morally right actions are those actions that maximize the pleasure and minimize the pain. Utilitarianism thinks the consequence of an action justifies the moral acceptability of means taken to reach that end and the result of actions outweigh any other considerations. In other words, they believe that end justifies the means. Utilitarianism believes an action is morally right if it results in pleasure; whereas it is wrong if it gives rise to pain.
Utilitarianism believes sacrificing one man to save thousands is okay because you maximize the happiness of whole community or the world. For utilitarianism consequences of actions matter, so right action maximize the amount of happiness. Utilitarianism does not consider personal relationship. For instance, there is fire and in this fire there is your son and a person who can cure cancer who will burn to the death, utilitarianism will say save the person who can cure the cancer because he will save all patients who have cancer and it will maximize the happiness in the world. According to utilitarianism, it is out duty to help people without worrying about consequences, for example, Mills thinks we should do charities as much as we can without having affected or damage on ourselves because giving charity will give maximize pleasure and minimize pain. Millâ€™s ethical view links happiness with morality because it makes sense with common beliefs about morality for example utilitarianism backs up murder is wrong. There are few act that are not good according to utilitarianism such as selfless act, for instance beating up wife gives pleasure to men where wife is selfless so this act is not morally right and good for utilitarianism.
Sometimes utilitarianism require us to commit morally reprehensible acts for instance, there is a terrorist who has a nuclear weapon aimed at your city and at the same time you have access to the child of insane terrorist, you can torture the child so you can get the terrorist to stop his action. In situation like this, utilitarianism might say to torture the child so you can save the whole city even though it is not morally right to torture small child. I think the major problem with utilitarianism in defining ethics as either happiness or pleasure is that happiness is a moral duty and it is not morality in and of itself. While pleasure is not a moral duty but rather a biological command to seek that which pleasure us, for example drugs, sex, music can give us pleasure but they have nothing to do with morality or ethics.
On the other hand, Kant believed in an ethical theory known as Deontology; that focus on the concept of duty rather than on any concept of right or wrong. His theory emphasize on the type of action rather than consequences of that action. Kant believes that moral decisions should be based on one duties and right of others and we should act morally regardless of consequences and act is considered moral if it is done for the sake of duty. For instance, a homeless man with brain damage in accident is brought to hospital and doctor realize that he does not have any families but deontologist will save man life as it is his duty to treat a patients. Utilitarianism might say let man die and use his organ to save as many people as possible to maximize the happiness of the world. However, according to deontologist allowing the man to die would not make that decision justify.
Kant believe that well being of each person should be an end to in itself and we should never treat someone as simple a means but always as a means to an end. According to Kant, moral rules are commands and it is demanded by reason and free person acts on reason and does not pay attention to influences that are nor rational. For example, there should not be any exception to moral rules or laws, therefore, it is wrong to kill people in all situations even in self defense that apply to everyone in every situation.
Kant believes that consequences do not matter because act of our consequences are not always in our control and things do not turn out, as we want. However, we can control our motives and the motives to what is right gives an act its moral worth. Kant believes we should use our morals as a guide when making decisions, for instance, there are four patients in the hospital that needs different organ to survive, and a regular person comes to the hospital for regular check up. According to utilitarianism, it is better to sacrifice one man to save others because it will maximize the happiness but deontologist will say it is immoral to kill an innocent person to maximize the happiness and we should not use person as a tool. Another difference between these two theories in situation like lie, Kant believes we should not lie in any circumstances because it is morally wrong and to lie it will make a person a means to an end which is not good. However, utilitarianism will say that it is okay to lie if it maximizes the happiness.