In philosophy, ressentiment (rəˌsɑ̃.tiˈmɑ̃; ʁə.sɑ̃.ti.mɑ̃) is one of the forms of resentment or hostility. The concept was of particular interest to some 19th century thinkers, most notably Friedrich Nietzsche. According to their use, ressentiment is a sense of hostility directed toward an object that one identifies as the cause of one's frustration, that is, an assignment of blame for one's frustration. The sense of weakness or inferiority complex and perhaps even jealousy in the face of the "cause" generates a rejecting/justifying value system, or morality, which attacks or denies the perceived source of one's frustration. This value system is then used as a means of justifying one's own weaknesses by identifying the source of envy as objectively inferior, serving as a defense mechanism that prevents the resentful individual from addressing and overcoming their insecurities and flaws. The ego creates an enemy to insulate themselves from culpability. Ressentiment as a concept gained popularity with Friedrich Nietzsche's writings. Walter Kaufmann ascribes his use of the term in part to the absence of a proper equivalent term in the German language, contending that this absence alone "would be sufficient excuse for Nietzsche", if not for a translator. The term came to form a key part of his ideas concerning the psychology of the 'master–slave' question (articulated in Beyond Good and Evil), and the resultant birth of morality. Nietzsche's chief development of ressentiment came in his book On the Genealogy of Morals; see esp §§ 10–11). Earlier it had been used by Søren Kierkegaard. notably in his Two Ages: A Literary Review. The term was also studied by Max Scheler in a monograph published in 1912 and reworked a few years later. Currently of great import as a term widely used in psychology and existentialism, ressentiment is viewed as an influential force for the creation of identities, moral frameworks and value systems. However, there is debate as to what validity these resultant value systems have, and to what extent they are maladaptive and destructive.