The Presocratics were 6 and 5 century BCE Greek thinkers who introduced a new way of inquiring into the world and the place of human beings in it. They were recognized in antiquity as the first philosophers and scientists of the Western tradition. This article is a general introduction to the most important Presocratic philosophers and the main themes of Presocratic thought. More detailed discussions can be found by consulting the articles on these philosophers (and related topics) in the SEP (listed below). The standard collection of texts for the Presocratics is that by H. Diels revised by W. Kranz (abbreviated as DK). In it, each thinker is assigned an identifying chapter number (e.g., Heraclitus is 22, Anaxagoras 59); then the reports from ancient authors about that thinker's life and thought are collected in a section of "testimonies" (A) and numbered in order, while the passages the editors take to be direct quotations are collected and numbered in a section of "fragments" (B). Alleged imitations in later authors are sometimes added in a section labeled C. Thus, each piece of text can be uniquely identified: DK 59B12.3 identifies line 3 of Anaxagoras fragment 12; DK 22A1 identifies testimonium 1 on Heraclitus. Corruption I): these thinkers were his predecessors in a particular sort of inquiry, and even though Aristotle thinks that they were all, for one reason or another, unsuccessful and even amateurish, he sees in them a similarity such that he can trace a line of continuity of both subject and method from their work to his own. The questions that the early Greek philosophers asked, the sorts of answers that they gave, and the views that they had of their own inquiries were the foundation for the development of philosophy as it came to be defined in the work of Plato and Aristotle and their successors. Perhaps the fundamental characteristic is the commitment to explain the world in terms of its own inherent principles. By contrast, consider the 7 century BCE poem of Hesiod, his Theogony (genealogy of the gods). Hesiod tells the traditional story of the Olympian gods, beginning with Chaos, a vague divine primordial entity or condition. From Chaos, a sequence of gods is generated, often by sexual congress, but sometimes no cause for their coming to be is given. The divine figures that thus arise are often connected with a part of the physical universe, or with some aspect of human experience, so his theogony is also a cosmogony (an account of the generation of the world). The divinities (and the associated parts of the world) come to be and struggle violently among themselves; finally Zeus triumphs and establishes and maintains an order of power among the others. Hesiod's world is one in which the major divinities are individuals who behave like superhuman beings (Gaia or earth, Ouranos or sky, Cronos-an unlocated regal power, Zeus); some of the others are personified characteristics (e.g., Momus, blame; and Dusnomia, lawlessness). For the Greeks, the fundamental properties of divinity are immortality (they...