Ataraxia (ἀταραξία) is a Greek term used by--amongst others--Pyrrho and Epicurus. Ataraxia is the Greek word for equanimity, sometimes translated as imperturbability.  It generally translates as tranquility, serenity, or peace, and it’s the telos or goal of all wholesome ethical philosophy. In Epicureanism, ataraxia was synonymous with the only true happiness possible for a person. It signifies the state of robust tranquillity that derives from eschewing faith in an afterlife, not fearing the Gods because They are distant and unconcerned with us, avoiding politics and vexatious people, surrounding oneself with trustworthy and affectionate friends and, most importantly, being an affectionate, virtuous person, worthy of trust.

Ataraxia is satisfaction with life as it is here and now, not seeking its perfection but accepting its limitations and never minding them. It’s the mental aboveness of one who’s learned to be happy and to live in a pleasant state always, regardless of conditions. Ataraxia is unconditional pleasure in living.

Note that ataraxia is not about eliminating doubt, but about eliminating the cause of the mental distress people experience when doubts assail their minds. This cause contains a desire for the certainty of knowledge coupled with a belief that such knowledge is possible; and when we desire something, we always desire more of it. The practice of ataraxia requires the acceptance of the inherent uncertainty of most of our opinions and calls us to stop searching for answers that do not exist in our world and can never be attained.

Epicurus insisted that ataraxia is a mindful, positive state of peaceful abiding which can be cultivated through certain disciplines, including the cultivation of deep gratitude to life, to nature, to one’s teachers and ancestors. Sextus Empiricus supplies an example of ataraxia:

"The Sceptic, in fact, had the same experience which is said to have befallen the painter Apelles. Once, they say, when he was painting a horse and wished to represent in the painting the horse's foam, he was so unsuccessful that he gave up the attempt and flung at the picture the sponge on which he used to wipe the paints off his brush, and the mark of the sponge produced the effect of a horse's foam. So, too, the Sceptics were in hopes of gaining quietude [ataraxia] by means of a decision regarding the disparity of the objects of sense and of thought, and being unable to effect this they suspended judgment; and they found that quietude, as if by chance, followed upon their suspense. [Outlines of Pyrrhonism 1.28—29]

How do we benefit by accepting a basic human ignorance? The reason is pragmatic. We benefit by releasing debilitating mental agitation. Where knowledge is unavailable, we can only make a choice. The those who practice ataraxia choose not to choose in cases where there are no clear conclusions and opposing positions continue to be asserted even while everyone knows they cannot all be true. The benefit is in letting go of any and all doubt an fear of that which will always remain uncertain.

Stoicism often made use of the term, as they too sought mental tranquillity and saw ataraxia as highly valuable. In Stoicism, however, ataraxia is not an end to be pursued for its own sake as it is in many other philosophical schools. Rather, it is a natural consequence that occurs in a person who pursues virtue.

Ataraxia is very important in Hellenic philosophy and in Hellenismos today. Christianity clings to many religious terms we use today--including the word ' religion', which is often seen as synonymous to Christianity. It's concepts of fear of Deity and death live on in many of our minds, even in those minds that were not formed by Christian ideology. In modern times, practicing ataraxia includes becoming aware of this influence and letting it go in favour of more ancient ways of philosophical thinking. In modern Hellenismos, ataraxia is an almost necessary practice to apply in order to get ethically and philosophically closer to the ancient Hellenes and through their way of thinking, the Theoi.