For most people morals are sets of rules that we ought to obey, they tell us what is right or wrong. Moral philosophers want to discover how these rules are justified, and at the logical consequences of moral or ethical beliefs.
The age of enlightenment saw a questioning of religious and traditional values. If religion is questioned, then so to is morality. Philosophers needed to base moral system on justifiable grounds.
Kant's moral system is based on rationality. It attempts to show how any rational being would agree to universal moral laws. Its influence has been enormous and modern philosophers still use Kant's ideas as a starting point for discussions on morality.
The other great ethical system of the post-enlightenment era is Utilitarianism. Proposed by the British philosopher Jeremy Bentham (1748-1832), the principal of utility is based on happiness and was seen as being a scientific approach to morality.
Critical philosophers of the nineteenth century were less certain that universal moral values could be upheld. For Marx morality and ethics were part of bourgeois ideology: sets of ideas that ignored the exploitative economic arrangements of society and contributed to False Consciousness.
Nietzsche looked at the origins of morality, and like Marx, saw moral systems as arising from the interests of social groups. For Nietzsche the individual had to go beyond accepted morality to create a new morality for himself.
In the twentieth century, there has been growing pessimism about the possibility of a universal moral system. Jean-Paul Sartre (1905-80) emphasised the subjective judgements that an individual must make in order to be "authentic".
Anglo-American philosophers have wondered whether philosophy could say anything meaningful at all about what is right or good, as they put it moral statements have no "truth value". For these analytic philosophers the role of philosophy is to analyse how we use moral concepts, rather than say what morality should be. Writers like A.J. Ayer (1910-89) suggested that moral statements simply express the moral sentiments or attitudes of the individual and that philosophy has no way of evaluating which set of moral statements is best.
For Kant human beings as moral agents are rational and autonomous (free to make choices). He thinks that as rational beings we are able to judge whether any action is moral by asking if the action is consistent with the categorical imperative.
One formulation of the categorical imperative is, "Act only on that maxim (intention) whereby at the same time you can will that it shall become a universal law". What Kant means by this is that they way that we judge an action to be moral is to universalise it: If I want to know if telling a lie on a particular occasion is justifiable, I must try to imagine what would happen if everyone was to lie. Kant thinks that any rational being would agree that a world in which there is no lying is preferable to one in which lying was common; in a society in which lying was common no one could trust the word of anyone else.
Another formulation is: "Always act to treat humanity, whether in yourself or in others, as an end in itself, never merely as a means." What Kant means by this is that a rational being should not be used as a means to another person's happiness; if we use another person as a means to our ends then we have removed that person's autonomy.
Jeremy Bentham (1748-1832) and John Stuart Mill (1806-1873) in Britain developed the moral theory called Utilitarianism. It aimed to give a method of moral judgement based on experience rather than dogma.
Bentham thought that an action was good if it increased pleasure, bad if it increased pain. An action or law would by good if it produced "The greatest happiness for the greatest number". He developed a "happiness calculus" in order to calculate for any action or law what the consequences in terms of pleasure or pain would be. Using these principals he designed a prison called the panopticon where punishment would be measured out according to the amount of pain caused by the offender.
Thomas Carlyle (1795-1881) called utilitarianism "pig philosophy"; as it appeared to base the goal of ethics on the swinish pleasures of the multitude. In the light of this criticism, J S Mill refined Bentham's theory by suggesting that there were higher and lower pleasures, and that the higher pleasures were preferable. As he puts it: "Better to be Socrates dissatisfied than a fool satisfied". By lower pleasures Mill meant pleasures of the flesh, and by higher pleasures, pleasures of the intellect. One consequence of Mill's modification was that it was no longer possible to use Bentham's "happiness calculus".
For Nietzsche there are two basic types of morality: master morality and slave morality. By this, he means that moral codes arise from people's social origins.
Master morality sees the noble as good and emphasises heroism, courage and individual greatness as can be found in the aristocratic morality of the ancient Greeks.
Slave morality is the morality of the weak. What harms the weak is called "evil", and what helps them is called good. Christian ethics are identified with slave morality.
Nietzsche thought that each individual needs to create their own moral system: the point of morality is to enable each individual to sublimate and control their passions, in order to emphasise the creativity inherent in their being.
Sartre is an atheist, and as such believed that individuals have no objective way of formulating morality. If we follow a moral system or religion, we are acting in "Bad faith" by denying that we have the responsibility for determining our own choices.
Like Nietzsche, Sartre believed that it is the individual who needs to create their own moral code. Sartre believed that individuals should act authentically, that is make choices based on the understanding that we are responsible for creating ourselves.