Master–slave morality is a central theme of Friedrich Nietzsche's works, in particular the first essay of On the Genealogy of Morality. Nietzsche argued that there were two fundamental types of morality: 'Master morality' and 'slave morality'. Slave morality values things like kindness, humility and sympathy, while master morality values pride, strength, and nobility. Master morality weighs actions on a scale of good or bad consequences unlike slave morality which weighs actions on a scale of good or evil intentions. What he meant by 'morality' deviates from common understanding of this term. For Nietzsche, a particular morality is inseparable from the formation of a particular culture. This means that its language, codes and practices, narratives, and institutions are informed by the struggle between these two types of moral valuation. Master–slave morality provides the basis of all exegesis of Western thought.
It is disputed whether Nietzsche advocated either of the two moralities.
Master morality 
Nietzsche defined master morality as the morality of the strong-willed. Nietzsche criticizes the view, which he identifies with contemporary British ideology, that good is everything that is helpful; what is bad is what is harmful. He argues that this view has forgotten the origins of the values, and thus it calls what is useful good on the grounds of habitualness - what is useful has always been defined as good, therefore usefulness is goodness as a value. He continues explaining, that in the prehistoric state, "the value or non-value of an action was derived from its consequences" but ultimately, "There are no moral phenomena at all, only moral interpretations of phenomena." For these strong-willed men, the 'good' is the noble, strong and powerful, while the 'bad' is the weak, cowardly, timid and petty. The essence of master morality is nobility. Other qualities that are often valued in master moralities are open-mindedness, courage, truthfulness, trust and an accurate sense of self-worth. Master morality begins in the 'noble man' with a spontaneous idea of the good, then the idea of bad develops as what is not good. "The noble type of man experiences itself as determining values; it does not need approval; it judges, 'what is harmful to me is harmful in itself'; it knows itself to be that which first accords honour to things; it is value-creating." In this sense, the master morality is the full recognition that oneself is the measure of all things. Insomuch as something is helpful to the strong-willed man it is like what he values in himself; therefore, the strong-willed man values such things as 'good'. Masters are creators of morality; slaves respond to master-morality with their slave-morality.
Slave morality 
Unlike master morality which is sentiment, slave morality is literally re-sentiment—revaluing that which the master values. This strays from the valuation of actions based on consequences to the valuation of actions based on "intention". As master morality originates in the strong, slave morality originates in the weak. Because slave morality is a reaction to oppression, it villainizes its oppressors. Slave morality is the inverse of master morality. As such, it is characterized by pessimism and cynicism. Slave morality is created in opposition to what master morality values as 'good'. Slave morality does not aim at exerting one's will by strength but by careful subversion. It does not seek to transcend the masters, but to make them slaves as well. The essence of slave morality is utility: the good is what is most useful for the whole community, not the strong. Nietzsche saw this as a contradiction. Since the powerful are few in number compared to the masses of the weak, the weak gain power by corrupting the strong into believing that the causes of slavery (viz., the will to power) are 'evil', as are the qualities they originally could not choose because of their weakness. By saying humility is voluntary, slave morality avoids admitting that their humility was in the beginning forced upon them by a master. Biblical principles of turning the other cheek, humility, charity, and pity are the result of universalizing the plight of the slave onto all humankind, and thus enslaving the masters as well. "The democratic movement is the heir to Christianity."—the political manifestation of slave morality because of its obsession with freedom and equality.
- "...the Jews achieved that miracle of inversion of values thanks to which life on earth has for a couple millennia acquired a new and dangerous fascination--their prophets fused 'rich', 'godless', 'evil', 'violent', 'sensual' into one and were the first to coin the word 'world' as a term of infamy. It is this inversion of values (with which is involved the employment of the word for 'poor' as a synonym for 'holy' and 'friend') that the significance of the Jewish people resides: with them there begins the slave revolt in morals."
This struggle between master and slave moralities recurs historically. According to Nietzsche, ancient Greek and Roman societies were grounded in master morality. The Homeric hero is the strong-willed man, and the classical roots of the Iliad and Odyssey exemplified Nietzsche's master morality. He calls the heroes "men of a noble culture", giving a substantive example of master morality. Historically, master morality was defeated as the slave morality of Christianity spread throughout the Roman Empire.
The essential struggle between cultures has always been between the Roman (master, strong) and the Judean (slave, weak). Nietzsche condemns the triumph of slave morality in the West, saying that the democratic movement is the "collective degeneration of man". He claimed that the nascent democratic movement of his time was essentially slavish and weak. Weakness conquered strength, slave conquered master, re-sentiment conquered sentiment. This resentment Nietzsche calls "priestly vindictiveness", which is the jealousy of the weak seeking to enslave the strong with itself. Such movements were, to Nietzsche, inspired by "the most intelligent revenge" of the weak. Nietzsche saw democracy and Christianity as the same emasculating impulse which sought to make all equal—to make all slaves.
Nietzsche, however, did not believe that humans should adopt master morality as the be-all-end-all code of behavior - he believed that the revaluation of morals would correct the inconsistencies in both master and slave morality - but simply that master morality was preferable to slave morality, although this is debatable. Walter Kaufmann disagrees that Nietzsche actually preferred master morality to slave morality. He certainly gives slave morality a much harder time, but this is partly because he believes that slave morality is modern society's more imminent danger. The Antichrist had been meant as the first book in a four-book series, Toward a Re-Evaluation of All Morals, which might have made his views more explicit, but Nietzsche was afflicted by mental collapse that rendered him unable to write the latter three books.
In other philosophy 
The notion that the strong-willed is not kind or helpful contrasts with the philosophy of Thomas Aquinas, who holds charity as "the greatest of virtues." According to Aquinas, a charitable man is happy and virtuous. Aquinas holds that the class of virtues denoted by fortitude is compatible with charity, and not in opposition to it.
An extreme notion that a virtuous man is "value-creating" contrasts with Aquinas's conception of a last end. According to Aquinas, man's last end is not determined by man: "all men agree in desiring the last end, which is happiness." Aquinas holds the choice of useful means to reach this last end as determined by man's free will, although he holds that certain habits are virtuous and thus predictably lead to happiness, provided that they are not pursued to excess. According to Aquinas, free will is thus a means to an end, but not the last end, as it can be helpful or unhelpful to the pursuit of happiness: those who choose to perform non-virtuous acts "turn from that in which their last end really consists: but they do not turn away from the intention of the last end, which intention they mistakenly seek in other things."
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 62. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 96. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1967). On The Genealogy of Morals. New York: Vintage Books. p. 39. ISBN 0-679-72462-1.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 63. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 122. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 125. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 118. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 153. ISBN 978-0-14-044923-5.
- Nietzsche, Friedrich (1973). Beyond Good and Evil. London: Penguin Books. p. 127. ISBN 978-0-14-044923-5.
- "SUMMA THEOLOGICA: Charity, considered in itself (Secunda Secundae Partis, Q. 23)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Humility (Secunda Secundae Partis, Q. 161)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Secunda Secundae Partis". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Fortitude (Secunda Secundae Partis, Q. 123)". Newadvent.org. Retrieved 2013-03-22.
- "Summa Theologica: Treatise On The Last End (QQ-5): Question. 1 - OF MAN'S LAST END (EIGHT ARTICLES)". Sacred-texts.com. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Free-will (Prima Pars, Q. 83)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Things in which man's happiness consists (Prima Secundae Partis, Q. 2)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: What is happiness (Prima Secundae Partis, Q. 3)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: Things that are required for happiness (Prima Secundae Partis, Q. 4)". Newadvent.org. Retrieved 2013-03-22.
- "SUMMA THEOLOGICA: The attainment of happiness (Prima Secundae Partis, Q. 5)". Newadvent.org. Retrieved 2013-03-22.
- Solomon, Robert C. and Clancy Martin. 2005. Since Socrates: A Concise Sourcebook of Classic Readings. London: Thomson Wadsworth. ISBN 0534633285.