#presocratic

• Alcmaeon — The standard Latinized form of the Greek name Alcmeon (Alkmaion); in history and philosophy, it refers to Alcmaeon of Croton (5th century BCE), a pre-Socratic philosopher and renowned medical theorist, considered among the first to perform anatomical dissections and propose the brain as the central seat of intelligence and perception. In mythology, he is one of the Epigoni, son of Amphiaraus and Eriphyle, who killed his mother to avenge his father.
• Alcmaeon — The Romanian form of the ancient Greek name Alkmaion; it primarily refers to Alcmaeon of Croton (5th century BCE), a famous pre-Socratic philosopher and medical theorist, historically recognized as a pioneer of anatomical dissections and for his revolutionary hypothesis that the brain is the central seat of thought and sensory perception. In mythology, he is one of the Epigoni, son of Amphiaraus, structurally trapped by fate in the tragedy of matricide.
• Anaxagoras — Anaxagoras of Clazomenae (c. 500 – 428 BC); a famous presocratic Greek philosopher who introduced into philosophical thought the structural notion of 'Nous' (the universal Mind or Reason) as an ordering force governing the primordial matter made of 'homeomeries' (eternal seeds of all things). He is historically recognized for moving the center of philosophy to Athens and for his rational explanations regarding eclipses and celestial phenomena.
• Anaximander — Anaximander of Miletus (c. 610 – 546 BC); a presocratic Greek philosopher of the Milesian school, disciple of Thales and master of Anaximenes. He is structurally recognized as the first thinker to have written a philosophical treatise in prose and to have identified the primordial principle of all things (arche) in the 'apeiron' (the boundless, infinite, or indefinite), an eternal substance in motion from which opposites separate.
• Anaximenes — Anaximenes of Miletus (c. 585 – 528 BC); a presocratic Greek philosopher, the last representative of the Milesian school, disciple of Anaximander. He structurally simplified the search for the primordial principle (arche) by identifying it as infinite air (aer), a divine and animated substance that, through the physical processes of rarefaction and condensation, gives rise to all elements and forms in the universe.
• Apeiron — A fundamental philosophical concept introduced by the pre-Socratic thinker Anaximander of Miletus, designating the infinite, indeterminate, boundless, and eternal primordial matter from which all things in the universe originate and into which they return. It represents the originating principle (arche) governed by an internal dynamic that generates opposites.
• First principle — A fundamental philosophical concept originating from Ancient Greece that designates the beginning, origin, first principle, or primordial substance from which all things derive and into which they eventually resolve. Structurally introduced by presocratic thinkers of the Milesian school, the term represents the ontological foundation of reality, explained variously through single cosmic elements like water, air, fire, or the indeterminate infinite.