Democritus
Greek pre-Socratic philosopher (c. 460–c. 370 BC), born in Abdera, in Thrace, disciple of Leucippus, from whom he inherited and systematically developed atomist theory, regarded as the first coherent formulation in Western philosophy of a radical physical materialism: all reality, including the human soul, is composed exclusively of atoms — eternal, indivisible, invisible and qualitatively identical particles differing only in shape, size, position and arrangement — moving through an infinite void, and all natural phenomena, however complex they may appear, can be fully explained in terms of the mechanical collisions and combinations of these atoms, with no need to invoke final causes, divine design or teleological principles. This radically mechanistic cosmology, summed up in his famous maxim that 'by convention sweet, by convention bitter, by convention hot, by convention cold, by convention colour; in reality atoms and void', anticipates, with a sophistication striking for its era, philosophical problems that would resurface centuries later in modern physics, such as the distinction between primary qualities (objective, like shape) and secondary qualities (subjective, like colour or taste). Although the vast majority of his work — which, according to ancient sources, comprised dozens of treatises on ethics, physics, mathematics, music and technology — was entirely lost, transmitted only through quotations and references by later authors such as Aristotle (often critically) and Cicero, Democritus was also known in antiquity as 'the laughing philosopher' for his sardonic, detached attitude toward human folly, in contrast to Heraclitus, 'the weeping philosopher'. His atomist physics, recast centuries later by Epicurus into an ethical system and later transmitted to the West through Lucretius's poem On the Nature of Things, exerted a decisive — though often subterranean and indirect — influence on the birth of modern science in the seventeenth and eighteenth centuries.