Epicurus (Epikouros or Ἐπίκουρος in Greek) (341 BC, Samos – 270 BC, Athens) was an ancient Greek philosopher, the founder of Epicureanism, one of the most popular schools of thought in Hellenistic Philosophy.
Epicurus was born into an Athenian émigré family; his parents, Neocles and Chaerestrate, both Athenian citizens, were sent to an Athenian settlement on the Aegean island of Samos. According to Apollodorus (reported by Diogenes Laertius at X.14-15), he was born on the seventh day of the month Gamelion in the third year of the 109th Olympiad, in the archonship of Sosigenes (about February 341 BCE). He returned to Athens at the age of 18 to serve in military training. The playwright Menander served in the same age-class of the ephebes as Epicurus.
He joined his father in Colophon after the Athenian settlers at Samos were expelled by Perdiccas after Alexander the Great died (c. 320 BCE). He spent the next several years in Colophon, Lampsacus, and Mytilene, where he founded his school and gathered many disciples. In the archonship of Anaxicrates (307 BCE-306 BCE), he returned to Athens where he formed The Garden, a school named for the garden he owned about halfway between the Stoa and the Academy that served as the school's meeting place.
Epicurus died in the second year of the 127th Olympiad, in the archonship of Pytharatus, at the age of 72. He reportedly suffered from kidney stones, and despite the prolonged pain involved, he is reported as saying in a letter to Idomeneus:
We have written this letter to you on a happy day to us, which is also the last day of our life. For strangury has attacked me, and also a dysentery, so violent that nothing can be added to the violence of my sufferings. But the cheerfulness of my mind, which arises from their collection of all my philosophical contemplation, counterbalances all these afflictions. And I beg you to take care of the children of Metrodorus, in a manner worth of the devotion shown by the youth to me, and to philosophy (Diogenes Laertius, X.22, trans. C.D. Yonge).
Epicurus' school had a small but devoted following in his lifetime. The primary members were Hermarchus, the financier Idomeneus, Leonteus and his wife Themista, the satirist Colotes, the mathematician Polyaenus of Lampsacus, and Metrodorus, the most famous popularizer of Epicureanism. This original school was based in Epicurus' home and garden. An inscription on the gate to the garden is recorded by Seneca in his Epistle XXI:
The school's popularity grew and it became, along with Stoicism and Skepticism, one of the three dominant schools of Hellenistic Philosophy, lasting strongly through the later Roman Empire. In Rome, Lucretius was the school's greatest proponent, composing On the Nature of Things, an epic poem, in six books, designed to recruit new members. The poem mainly deals with Epicurean philosophy of nature. Another major source of information is the Roman politician and amateur philosopher Cicero, although he was highly critical of Epicureanism. Another ancient source is Diogenes of Oenoanda, who composed a large inscription at Oenoanda in Lycia.
A library, dubbed the Villa of the Papyri, in Herculaneum, owned by Julius Caesar's father-in-law, Lucius Calpurnius Piso Caesoninus, was preserved by the eruption of Vesuvius in 79 AD, and was found to contain a large number of works by Philodemus, a late Hellenistic Epicurean, and Epicurus himself, attesting to the school's enduring popularity. The task of unrolling and deciphering the charred papyrus scrolls continues today.
After the official approval of Christianity by Constantine, Epicureanism was repressed. Epicurus' theory that the gods were unconcerned with human affairs had always clashed strongly with the Judeo-Christian God, and the philosophies were essentially irreconcilable. For example, the word for a heretic in the Talmudic literature is "Apikoros". Lactantius criticizes Epicurus at several points throughout his Divine Institutes. The school endured a long period of obscurity and decline. However, there was a resurgance of atomism among scientists in the 18th and 19th Centuries, and in the late 20th Century, the school was revived.
Epicurus' teachings represented a departure from the other major Greek thinkers of his period, and before, but was nevertheless founded on many of the same principles as Democritus. Like Democritus, he was an atomist, believing that the fundamental constituents of the world were uncuttable little bits of matter (atoms) flying through empty space (void). Everything that occurs is the result of the atoms colliding, rebounding, and becoming entangled with one another, with no purpose or plan behind their motions. His theory differs from the earlier atomism of Democritus because he admits that atoms do not always follow straight lines but their direction of motion may occasionally exhibit a 'swerve'. This allowed him to avoid the determinism implicit in the earlier atomism and to affirm free will.
He admitted women and slaves into his school, and was one of the first Greeks to break from the god-fearing and god-worshipping tradition common at the time, even while affirming that religious activities are useful as a way to contemplate the gods and to use them as an example of the pleasant life. Epicurus participated in the activities of traditional Greek religion, but taught that one should avoid holding false opinions about the gods. The gods are immortal and blessed and men who ascribe any additional qualities that are alien to immortality and blessedness are, according to Epicurus, impious. The gods do not punish the bad and reward the good as the common man believes. The opinion of the crowd is, Epicurus claims, that the gods "send great evils to the wicked and great blessings to the righteous who model themselves after the gods.", when in reality the gods do not concern themselves at all with human beings.
Epicurus' philosophy is based on the theory that all good and bad derive from the sensations of pleasure and pain. What is good is what is pleasurable, and what is bad is what is painful. Pleasure and pain were ultimately, for Epicurus, the basis for the moral distinction between good and bad. If pain is chosen over pleasure in some cases it is only because it leads to a greater pleasure. Moral reasoning is a matter of calculating the benefits and costs in terms of pleasure and pain. Although Epicurus was commonly misunderstood to advocate the rampant pursuit of pleasure, what he was really after was the absence of pain (both physical and mental, i.e., anxiety) - a state of satiation and tranquility that was free of the fear of death and the retribution of the gods. When we do not suffer pain, we are no longer in need of pleasure.
Epicurus explicitly warned against overindulgence because it often leads to pain. For instance, in what might be described as a "hangover" theory, Epicurus warned against pursuing love too ardently. However, having a circle of friends you can trust is one of the most important means for securing a tranquil life.
Epicurus also believed (in contradistinction to Aristotle) that death was not to be feared. When a man dies, he does not feel the pain of death because he no longer is and he therefore feels nothing. Therefore, as Epicurus famously said, "death is nothing to us.",when we exist death is not, and when death exists we are not. All sensation and consciousness ends with death and therefore in death there is neither pleasure nor pain. The fear of death arises from the false belief that in death there is awareness.
In his epistemology he emphasized the senses, and his Prinicple of Multiple Explanations is an early contribution to the philosophy of science: if several theories are consistent with the observed data, retain them all. "There are also some things for which it is not enough to state a single cause, but several, of which one, however, is the case. Just as if you were to see the lifeless corpse of a man lying far away, it would be fitting to state all the causes of death in order that the single cause of this death may be stated. For you would not be able to establish conclusively that he died by the sword or of cold or of illness or perhaps by poison, but we know that there is something of this kind that happened to him." (Lucretius)
In contrast to the Stoics, Epicureans showed little interest in participating in the politics of the day, since doing so leads to trouble. He instead advocated seclusion. His garden can be compared to present-day communes.
The most well-known Epicurean verse, which epitomizes his philosophy, is lathe biōsas λάθε βιώσας (Plutarchus De latenter vivendo 1128c; Flavius Philostratus Vita Apollonii 8.28.12), meaning "live secretly", "get through life without drawing attention to yourself", i. e. live without pursuing glory or wealth or power, but anonymously, enjoying little things like food, the company of friends, etc.
Main article: Tetrapharmakos.
Tetrapharmakos, or, "The four-part cure," is Epicurus' overall statement of how to live the happiest possible life. This poetic doctrine was handed down by an anonymous Epicurean who summed up Epicurus' philosophy on happiness in four simple lines:
Don't fear god,
Don't worry about death;
What is good is easy to get, and
What is terrible is easy to endure.
(Philodemus, Herculaneum Papyrus, 1005, 4.9-14)
Epicurus' philosophy of the physical world is found in "Letter to Herodotus": Diogenes Laertius 10.34-83. Below is its paraphrase.
If a limited form lives within an unlimited void, the form could only wander aimlessly about, because what is unlimited is ungraspable; meaning, the limited form would travel forever, for it does not have any obstacles. The void would have to be limited in quality and the form of an unlimited quality, for an unlimited form can oscillate and seemingly grasp—practically, but not literally—an unlimited number of spots within the limited void. So therefore all living things on Earth are unlimited, and the Earth on which they live and the universe around it, is limited. (This could be furthered ad nauseam in that the universe is limited and that the galaxy is unlimited, etc.)
Forms can change, but not their inherent qualities, for change can only affect their shape. Some things can be changed and some things cannot be changed because forms that are unchangeable cannot be destroyed if certain attributes can be removed; for attributes not only have the intention of altering an unchangeable form, but also the inevitable possibility of becoming—in relation to the form’s disposition to its present environment—both an armor and a vulnerability to the its stability.
Further proof that there are unchangeable forms and their inability to be destroyed, is the concept of the “non-evident.” A form cannot come into being from the void—which is nothing; it would be as if all forms come into being spontaneously, needless of reproduction. The implied meaning of “destroying” something is to undo its existence, to make it not there anymore, and this cannot be so: if the void is that which does not exist, and if this void is the implied destination of the destroyed, then the thing in reality cannot be destroyed, for the thing (and all things) could not have existed in the first place (as Lucretius said, ex nihilo nihil fit: nothing comes from nothing). This totality of forms is eternal and unchangeable.
Atoms move, in the appropriate way, constantly and for all time. Forms first come to us in images or “films”--outlines of their true selves. For an image to be perceived by the human eye, the “atoms” of the image must cross a great distance at enormous speed and must not encounter any conflicting atoms along the way. The presents of atomic resistance equal atomic slowness; whereas, if the path is deficient of atomic resistance, the traversal rate is much faster (and clearer). Because of resistance, forms must be unlimited (unchangeable and able to grasp any point within the viod) because, if they weren't, a form's image would not come from a single place, but fragmented and from several places. This confirms that a single form cannot be at multiple places at the same time.
And the senses warrant us other means of perception: hearing and smelling. As in the same way an image traverses through the air, the atoms of sound and smell traverse the same way. This perceptive experience is itself the flow of the moving atoms; and like the changeable and unchangeable forms, the form from which the flow traverses is shed and shattered into even smaller atoms, atoms of which still represent the original form, but they are slightly disconnected and of diverse magnitudes. This flow, like that of an echo, reverberates (off one's senses) and goes back to its start; meaning, one’s sensory perception happens in the coming, going, or arch, of the flow; and when the flow retreats back to its starting position, the atomic image is back together again: thus when one smells something one has the ability to see it too.
And this leads to the question of how atomic speed and motion works. Epicurus says that there are two kinds of motion: the straight motion and the curved motion, and its motion traverse as fast as the speed of thought.
Elements of Epicurean philosophy have resonated and resurfaced in various diverse thinkers and movements throughout Western intellectual history. The Epicurean paradox is a famous argument against the existence of an all-powerful and providential God. The paradox is quoted as this:
"God either wants to eliminate bad things and cannot, or can but does not want to, or neither wishes to nor can, or both wants to and can. If he wants to and cannot, he is weak -- and this does not apply to god. If he can but does not want to, then he is spiteful -- which is equally foreign to god's nature. If he neither wants to nor can, he is both weak and spiteful and so not a god. If he wants to and can, which is the only thing fitting for a god, where then do bad things come from? Or why does he not eliminate them?"--Epicurus (from "The Epicurus Reader", translated and edited by Brad Inwood and L.P. Gerson, Hackett Publishing, 1994, p. 97)
Epicurus did not, however, deny the existence of Gods, but he did not think of them along the lines that lead to this paradox, but rather as blissful and immortal beings inhabiting the metakosmia, empty spaces between worlds in the vastness of infinite space.
Epicurus was one of the first thinkers to develop the notion of justice as a social contract. He defined justice as an agreement "neither to harm nor be harmed." The point of living in a society with laws and punishments is to be protected from harm so that one is free to pursue happiness. Because of this, laws that do not help contribute to promoting human happiness are not just.
This was later picked up by the democratic thinkers of the French Revolution, and others, like John Locke, who wrote that people had a right to "life, liberty, and property." To Locke, one's own body was part of their property, and thus one's right to property would theoretically guarantee safety for their persons, as well as their possessions.
This triad was carried forward into the American freedom movement and Declaration of Independence, by American founding father, Thomas Jefferson, as "life, liberty, and the pursuit of happiness."
Karl Marx's doctoral thesis was on "The Difference Between the Democritean and Epicurean Philosophy of Nature." 
Epicurus was also a significant source of inspiration and interest for Friedrich Nietzsche. Nietzsche cites his affinities to Epicurus in a number of his works, including The Gay Science, Beyond Good and Evil, and his private letters to Peter Gast. Nietzsche was attracted to, among other things, Epicurus' ability to maintain a cheerful philosophical outlook in the face of painful physical ailments. Nietzsche also suffered from a number of sicknesses during his lifetime. However, he thought that Epicurus' conception of happiness as freedom from anxiety was too passive and negative.
In a purposefully unfavourable expression, Epicurus is titled in Modern Greek idiom as the so-called "Dark Philosopher".