Thumos (also commonly spelled 'thymos'; Greek: ) is a Greek word expressing the concept of "spiritedness" (as in "spirited stallion" or "spirited debate"). The word indicates a physical association with breath or blood and is also used to express the human desire for recognition. It is not a somatic feeling, as nausea and giddiness are.
In Homer's works, thumos was used to denote emotions, desire, or an internal urge. Thumos was a permanent possession of living man, to which his thinking and feeling belonged. When a Homeric hero is under emotional stress, he may externalize his thumos and converse with or scold it.
Plato's Phaedrus and his later work The Republic discuss thumos as one of the three constituent parts of the human psyche. In the Phaedrus, Plato depicts logos as a charioteer driving the two horses eros and thumos (erotic love and spiritedness are to be guided by logos). In the Republic (Book IV) soul becomes divided into (See Plato's tripartite theory of soul):
Plato suggested we have three parts of our soul, which in some combination makes our destined vocation that makes us better in, this is a hidden basis for developing ideas that are innate ideas. Thumos may draw from this to strengthen man with our reasoning, this tripartite division is as follows:
Democritus used "euthymia" (i.e. "good thumos") to refer to a condition in which the soul lives calmly and steadily, being disturbed by no fear, superstition, or other passions. For Democritus euthymia was one of the root aspects the goal of human life.
Achilles', in the Illiad, cares for his own honour, he keeps god and deities in his heart; "...the thunderous lord of Hera might grant you the winning of glory, you must not set your mind on fighting the Trojans, whose delight is in battle, without me. So you will diminish my honour." 
"Megalothymia" refers to the need to be recognized as superior to others, while "isothymia" is the need to be recognized as merely equal to others. Both terms are neoclassical compounds, coined by Francis Fukuyama.
In his book The End of History and the Last Man, the author mentions "thymos" in relation to liberal democracy and recognition. He relates Socrates' ideas about Thymos and desire to how people want to be recognized within their government. Problems emerge when other people do not recognize another's Thymos, and therefore do not provide the justice that it requires. In order for people to exist in harmony, Fukuyama argues, isothymia rather than megalothymia must be used to satisfy the human need for recognition. Any system that creates political inequality is necessarily feeding the megalothymia of some members while denying it to others.
Fukuyama explains how Thymos relates to history with the example of anti-communism in relation to the Soviet Union, Eastern Europe, and China. He states, "We cannot understand the totality of the revolutionary phenomenon unless we appreciate the working of thymotic anger and the demand for recognition that accompanied communism's economic crisis."
Harvey Mansfield, author of the 2006 book on Manliness, bringing Thumos to political science, in relation to thumos; "Politics is about what makes you angry, not so much about what you want. Your wants do matter, but mainly because you feel you are entitled to have them satisfied and get angry when they are not." Politics, which political science misses; "is about who deserves to be more important."
Mansfield says "... people want to stand for something, which means opposing those who stand for something else."
Robert Kagan defines Thumos as; "a spiritedness and ferocity in defence of clan, tribe, city, or state." Kagan's argument is men in Western civilization are lacking in thumos, manly virtue, it is what leads many men to self-sacrifice, men must preserve enough thumos to be prepared to die for their country, lest they become decadent and ultimately subservient.