The forgotten 6th-century thinker who predicted the laws of inertia

Ideas & Philosophy · Published 2 October 2026 Swipe more like this →

In short: Long before Galileo’s famous experiments, a Byzantine scholar was already dismantling Aristotelian physics. By observing falling weights, John Philoponus proposed a revolutionary idea: that motion is sustained by an internal energy, laying the essential groundwork for the modern scientific understanding of how objects move through space.

Living in Alexandria around 490–570 AD, John Philoponus—often called John the Grammarian—was far more than a mere commentator. While his contemporaries adhered to the Aristotelian tradition, Philoponus used empirical observation to challenge long-held dogmas. His most significant scientific contribution was the 'theory of impetus.' He argued that an object continues to move because a specific energy is imparted to it by the mover, which eventually exhausts itself. This concept served as a vital precursor to the modern principle of inertia.

Philoponus’s methodology was strikingly modern. In his critiques of Aristotle’s Physics, he rejected the notion that a falling object's speed is strictly determined by its weight. Instead, he noted that when dropping two weights of different masses from the same height, the difference in their fall times is remarkably small. He also pioneered the idea of space as a three-dimensional, homogeneous medium, a concept that later influenced Renaissance thinkers like Galileo Galilei and Pico della Mirandola.

However, his intellectual journey was fraught with theological conflict. A committed Miaphysite, Philoponus used philosophy to defend Christian doctrines, such as the creation of the world, against Neoplatonic arguments for an eternal universe. These radical views—including his rejection of Aristotelian dynamics—made him a controversial figure. His theological stances were so polarizing that the Third Council of Constantinople eventually branded his positions as Tritheistic. Despite this posthumous condemnation, his ideas survived through Arabic translations, deeply influencing Islamic scholars like Avicenna and later Western thinkers like Buridan.

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