The Presocratics are called the first Greek philosophers, who appeared before Socrates and are also referred to as natural philosophers, as well as the earliest of the sophists. Their main focus of inquiry was the origin of the world and the fundamental structure of nature.

Philosophy was born in Ionia in the 6th century BC with the three Milesians, Thales, Anaximander, and Anaximenes. Thales is the first to pose the cosmological problem. As the first cause and origin of beings, he proposed water, thus introducing a single interpretative principle, and indeed a material one, for all phenomena.

Anaximander's successor considered the infinite as the principle of beings. Within the one, the infinite, lie generative powers that give rise to pairs of opposites, which are governed by inherent laws and causal relationships, such that the world presents itself as a self-sufficient and self-regulating system.

A contemporary but younger than Anaximander, Anaximenes seems to continue his thought, as he named air the source of all things, which he regarded as infinite and responsible for natural phenomena.

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