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Why did Aristotle rely so strongly on observation in scientific research?

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Marble bust of Aristotle with a beard and draped robe, showing detailed facial features and wavy hair, set against a dark background. — Aristotle Aristotle, detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust (c. 325 bce); in the Museo Nazionale Romano, Rome.

Aristotle’s reliance on observation was rooted in his rejection of Plato’s theory of transcendent Forms. While Plato argued that the physical world was merely an imperfect copy of a separate, ideal realm, Aristotle maintained that the world of perceived things is the real world.1

For Aristotle, knowledge begins with the senses. He believed that the human mind grasps universal truths—which he called katholou—directly from individual things in the physical world. Because he viewed the natural world as the primary object of study, he became an avid collector of empirical evidence, encouraging his students to study the actual institutions, biological structures, and behaviors of the world to understand how they functioned.12

This empirical approach was central to his teleology, or the doctrine of purposiveness. By observing how living beings develop from seeds to mature adults, he sought to understand the "purpose" or "perfection" inherent in nature. Consequently, his scientific research—ranging from comparative anatomy to political theory—was built upon the systematic examination of the physical environment rather than abstract speculation.12