Euthymia (, "gladness, good mood, serenity"—literally "good

thumos ''Thumos'', also spelled ''thymos'' (), is the Ancient Greece, Ancient Greek concept of (as in "a spirited stallion" or "spirited debate"). The word indicates a physical association with breath or blood and is also used to express the human desi ...

") is a central concept in the moral thoughts of

Democritus Democritus (, ; , ''Dēmókritos'', meaning "chosen of the people"; – ) was an Ancient Greece, Ancient Greek Pre-Socratic philosophy, pre-Socratic philosopher from Abdera, Thrace, Abdera, primarily remembered today for his formulation of an ...

, who presents it as an ideal disposition of mind corresponding to a form of equanimity, a calm affectivity and relative steadiness of the soul.

Diogenes Laërtius Diogenes Laërtius ( ; , ; ) was a biographer of the Greek philosophers. Little is definitively known about his life, but his surviving book ''Lives and Opinions of Eminent Philosophers'' is a principal source for the history of ancient Greek ph ...

records Democritus' view as follows: "The chief good he asserts to be cheerfulness (euthymia); which, however, he does not consider the same as pleasure; as some people, who have misunderstood him, have fancied that he meant; but he understands by cheerfulness, a condition according to which the soul lives calmly and steadily, being disturbed by no fear, or superstition, or other passion."

Seneca's ''tranquillitas''

In his dialogue '' De Tranquillitate Animi'', Seneca translates ''euthymia'' as ''tranquillitas'' (latin for "tranquility" or "peace of mind"):

The Greeks call this calm steadiness of mind ''euthymia'', and Democritus's treatise upon it is excellently written: I call it peace of mind 'tranquillitas''

Seneca's dialogue is intended as a remedy for the absence of ''euthymia'' of his friend Serenus, who asks him for help:

erenus:Not to multiply examples, I am in all things attended by this weakness of a well-meaning mind, to whose level I fear that I shall be gradually brought down, or what is even more worrying, that I may always hang as though about to fall, and that there may be more the matter with me than I myself perceive: for we take a friendly view of our own private affairs, and partiality always obscures our judgment. ..I beg you, therefore, if you have any remedy by which you could stop this vacillation of mine, to deem me worthy to owe my peace of mind to you.

Serenus' problem is that, despite recognising the validity of the Stoic principles by which he lives his life, his strength to follow them sometimes wavers. The opposite of this weakness, or vacillation, is the steadiness of mind, or tranquillity, defined by Seneca as follows:

eneca:What we are seeking, then, is how the mind may always pursue a steady, unruffled course, may be pleased with itself, and look with pleasure upon its surroundings, and experience no interruption of this joy, but abide in a peaceful condition without being ever either elated or depressed: this will be "peace of mind". 'tranquillitas''/blockquote> Seneca's euthymia, or tranquillity, must not be confused with the idea of
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, who misquotes (indicating no reference) Seneca's work ''On the tranquility of the mind'', wrongly defining euthymia as "believing in yourself and trusting that you are on the right path, and not being in doubt by following the myriad footpaths of those wandering in every direction".

See also
*
Ataraxia In Ancient Greek philosophy, ( Greek: , from indicating negation or absence and with the abstract noun suffix ), generally translated as , , , or , is a lucid state of robust equanimity characterized by ongoing freedom from distress and wo ...
*
Thumos ''Thumos'', also spelled ''thymos'' (), is the Ancient Greece, Ancient Greek concept of (as in "a spirited stallion" or "spirited debate"). The word indicates a physical association with breath or blood and is also used to express the human desi ...
*
Euthymia (medicine) In psychiatry and psychology, euthymia is a normal, tranquil mental state or mood. People with mood disorders, including major depressive disorder and bipolar disorder Bipolar disorder (BD), previously known as manic depression, is a me ...

References
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Sources

Democritus: Ethics
– ''
Stanford Encyclopedia of Philosophy The ''Stanford Encyclopedia of Philosophy'' (''SEP'') is a freely available online philosophy resource published and maintained by Stanford University, encompassing both an online encyclopedia of philosophy and peer-reviewed original publication ...
'' Concepts in ancient Greek ethics Happiness