Epicurean Atomism

http://plato.stanford.edu/entries/atomism-ancient/#7

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Democritus' atomism was revived in the early Hellenistic period, and an atomist school founded in Athens about 306, by Epicurus (341–270 BCE). The Epicureans formed more of a closed community than other schools, and promoted a philosophy of a simple, pleasant life lived with friends. The community included women, and some of its members raised children. The works of the founder were revered and some of them were memorized, a practice that may have discouraged philosophical innovation by later members of the school.

Epicurus seems to have learned of atomist doctrine through Democritus' follower Nausiphanes. Because Epicurus made some significant changes in atomist theory, it is often thought that his reformulation of the physical theory is an attempt to respond to Aristotle's criticisms of Democritus. Even more significant, however, is the increasing centrality of ethical concerns to Epicurus' atomism, and the importance of the view that belief in an atomist physical theory helps us live better lives.

Epicurus takes to heart a problem Democritus himself recognized (see 2. above), which is that atomist theory threatens to undermine itself if it removes any trust we can place in the evidence of the senses, by claiming that colors, etc. are unreal. He notoriously said that ‘all perception is true,’ apparently distinguishing between the causal processes which impact our senses, all of which originate with the films of atoms sloughed off by objects, and the judgments we make on the basis of them, which may be false. Reasoning to truths about things that are not apparent—like the existence of atoms—depends on the evidence of the senses, which is always true in that it consists of impacts from actually existing films. For particular phenomena, like meteorological events, Epicurus endorses the existence of multiple valid explanations, acknowledging that we may have no evidence for preferring one explanation over another.

It may be that Epicurus was less troubled by any such epistemological uncertainties because of his emphasis on the value of atomist theory for teaching us how to live the untroubled and tranquil life. Denying any divine sanction for morality, and holding that the experience of pleasure and pain are the source of all value, Epicurus thought we can learn from atomist philosophy that pursuing natural and necessary pleasures—rather than the misleading desires inculcated by society—will make pleasure readily attainable. At the same time, we will avoid the pains brought on by pursuing unnatural and unnecessary pleasures. Understanding, on the basis of the atomist theory, that our fears of the gods and of death are groundless will free us from our chief mental pains.

Epicurus made significant changes to atomist physical theory, and some of these have been traced to Aristotle's criticisms of Democritus. It seems that Democritus did not properly distinguish between the thesis of the physical uncuttability of atoms and that of their conceptual indivisibility: this raises a problem about how atoms can have parts, as evidenced by their variations in shape or their ability to compose a magnitude, touching one another in a series on different sides. Epicurus distinguished the two, holding that uncuttable atoms did have conceptually distinct parts, but that there was a lowest limit to these.

Epicurus' view of the motion of atoms also differs from Democritus'. Rather than talking of a motion towards the center of a given cosmos, possibly created by the cosmic vortex, Epicurus grants to atoms an innate tendency to downward motion through the infinite cosmos. The downward direction is simply the original direction of atomic fall . This may be in response to Aristotelian criticisms that Democritus does not show why atomic motion exists, merely saying that it is eternal and that it is perpetuated by collisions. Moreover, although this is not attested in the surviving writings of Epicurus, authoritative later sources attribute to him the idea that it belongs to the nature of atoms occasionally to exhibit a slight, otherwise uncaused swerve from their downward path. This is thought to explain why atoms have from infinite time entered into collisions instead of falling in parallel paths: it is also said, by Lucretius, to enter into the account of action and responsibility. 

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