Epicureanism
Authors: Sedley David 
Published: September 2018

Epicureanism is one of the three dominant philosophies of the Hellenistic age. The school was founded by Epicurus (341–271 bc) (see Prolēpsis). Only small samples and indirect testimonia of his writings now survive, supplemented by the poem of the Roman Epicurean Lucretius, along with a mass of further fragmentary texts and secondary evidence. Its main features are an anti-teleological physics, an empiricist epistemology and a hedonistic ethics.
Epicurean physics developed out of the fifth-century atomist system of Democritus. The only per se existents are bodies and space, each of them infinite in quantity. Space includes absolute void, which makes motion possible, while body is constituted out of physically indissoluble particles, ‘atoms’. Atoms are themselves further measurable into sets of absolute ‘minima’, the ultimate units of magnitude. Atoms are in constant rapid motion, at equal speed (since in the pure void there is nothing to slow them down). Stability emerges as an overall property of compounds, which large groups of atoms form by settling into regular patterns of complex motion. Motion is governed by the three principles of weight, collisions and a minimal random movement, the ‘swerve’, which initiates new patterns of motion and obviates the danger of determinism. Atoms themselves have only the primary properties of shape, size and weight. All secondary properties, for example, colour, are generated out of atomic compounds; given their dependent status, they cannot be added to the list of per se existents, but it does not follow that they are not real. Our world, like the countless other worlds, is an accidentally generated compound, of finite duration. There is no divine mind behind it. The gods are to be viewed as ideal beings, models of the Epicurean good life, and therefore blissfully detached from our affairs.
The foundation of the Epicurean theory of knowledge (‘Canonic’) is that ‘all sensations are true’ - that is, representationally (not propositionally) true. In the paradigm case of sight, thin films of atoms (‘images’) constantly flood off bodies, and our eyes mechanically register those which reach them, neither embroidering nor interpreting. These primary visual data (like photographs, which ‘cannot lie’) have unassailable evidential value. But inferences from them to the nature of external objects themselves involves judgment, and it is there that error can occur. Sensations thus serve as one of the three ‘criteria of truth’, along with feelings, a criterion of values and psychological data, and prolēpseis, naturally acquired generic conceptions. On the basis of sense evidence, we are entitled to infer the nature of microscopic or remote phenomena. Celestial phenomena, for example, cannot be regarded as divinely engineered (which would conflict with the prolēpsis of god as tranquil), and experience supplies plenty of models adequate to explain them naturalistically. Such grounds amount to consistency with directly observed phenomena, and are called ouk antimarturēsis, ‘lack of counterevidence’. Paradoxically, when several alternative explanations of the same phenomenon pass this test, all must be accepted as true. Fortunately, when it comes to the foundational tenets of physics, it is held that only one theory passes the test.
In ethics, pleasure is the one good and our innately sought goal, to which all other values are subordinated. Pain is the only bad, and there is no intermediate state. Bodily pleasure becomes more secure if we adopt a simple lifestyle which satisfies only our natural and necessary desires, with the support of like-minded friends. Bodily pain, when inevitable, can be outweighed by mental pleasure, which exceeds it because it can range over past, present and future enjoyments. The highest pleasure, whether of soul or of body, is a satisfied state, ‘static pleasure’. The short-term (‘kinetic’) pleasures of stimulation can vary this state, but cannot make it more pleasant. In striving to accumulate such pleasures, you run the risk of becoming dependent on them and thus needlessly vulnerable to fortune. The primary aim should instead be the minimization of pain. This is achieved for the body through a simple lifestyle, and for the soul through the study of physics, which offers the most prized ‘static’ pleasure, ‘freedom from disturbance’ (ataraxia), by eliminating the two main sources of human anguish, the fears of god and of death. It teaches us that cosmic phenomena do not convey divine threats, and that death is mere disintegration of the soul, with hell an illusion. Being dead will be no worse than not having yet been born. Physics also teaches us how to evade determinism, which would turn moral agents into mindless fatalists: the indeterministic ‘swerve’ doctrine (see above), along with the logical doctrine that future-tensed propositions may be neither true nor false, leaves the will free.
Although Epicurean groups sought to opt out of public life, they respected civic justice, which they analysed not as an absolute value but as one perpetually subject to revision in the light of changing circumstances, a contract between humans to refrain from harmful activity in their own mutual interest.