The Fragments of the Pre-Socratics

Diels–Kranz (DK) numbering is the standard system for referencing the works of the ancient Greek pre-Socratic philosophers, based on the collection of quotations from and reports of their work, Die Fragmente der Vorsokratiker (The Fragments of the Pre-Socratics), by Hermann Alexander Diels. The Fragmente was first published in 1903, was later revised and expanded three times by Diels, and was finally revised in a fifth edition (1934–7) by Walther Kranz and again in a sixth edition (1952). In Diels-Kranz, each passage, or item, is assigned a number which is used to uniquely identify the ancient personality with which it is concerned, and the type of item given. Diels-Kranz is used in academia to cite pre-Socratic philosophers, and the system also encompasses Sophists and pre-Homeric poets such as Orpheus, who were not necessarily philosophers as-such, but were also active figures in ancient Greece, preceding Socrates.

Stephanus pagination is the comparable system for referring to Plato, and Bekker numbering is the comparable system for referring to Aristotle.

The works of the pre-Socratics have not survived extant to the present day. Our knowledge of them exists only through references in the works of later philosophers (known as doxography) in the form of quotations and paraphrases. For example, our knowledge of Thales of Miletus comes largely from the works of Aristotle, who lived centuries after him. Another interesting example of such a source is Hippolytus of Rome, whose polemic Refutation of All Heresies is a source of many direct quotations of Heraclitus as well as of other philosophers, thereby perpetuating the work of those he was refuting.

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