Aristotle (384–322 BCE) remains one of the most influential figures in Western intellectual history, shaping fields from logic to biology. His extensive natural philosophy sought a comprehensive explanation for the physical world and how things change. Ancient Greek thinkers debated the fundamental nature of reality and the ultimate composition of matter. Aristotle’s conclusions defined the scientific understanding of the world for nearly two millennia, directly challenging another influential concept of the time.
The Preceding Theory of Atomism
Before Aristotle, Leucippus and his student Democritus developed the theory of atomism in the fifth century BCE. This model posited that all matter was composed of eternal, indivisible particles they called atomos, meaning “uncuttable.” These fundamental units moved continuously through an infinite expanse of empty space, which they termed the void.
The atomists argued that the world arose from differences in the atoms’ shape, size, and arrangement. Change, such as a substance appearing or disappearing, was merely the joining or separating of these indestructible particles. This purely physical view reduced all of nature to atoms and the void.
Aristotle’s Rejection of Indivisible Particles
Aristotle rejected the atomist theory, concluding that indivisible particles were impossible. His primary objection centered on the necessary condition for atomism: the existence of the void, or absolute empty space. Aristotle argued against this concept, famously stating that “nature abhors a vacuum.”
He reasoned that motion in a complete vacuum would meet no resistance, causing any object to travel instantaneously at infinite speed, which he considered absurd. Furthermore, a thrown object would continue moving indefinitely without a medium to resist it. Since motion was observable and finite, Aristotle concluded that the void could not exist, meaning matter must be continuous and infinitely divisible. This eliminated the possibility of atoms as conceived by Democritus.
The Doctrine of the Four Elements
Instead of relying on atoms, Aristotle developed a theory of matter based on four fundamental elements: Earth, Water, Air, and Fire. These were not fixed particles but changeable substances. This allowed his system to explain the constant transformations observed in nature, such as water turning to steam or wood turning to ash.
Each element was defined by possessing a combination of two primary qualities: Hot, Cold, Wet, and Dry. Fire was Hot and Dry, Water was Cold and Wet, Earth was Cold and Dry, and Air was Hot and Wet.
Transformation between elements occurred when one of these qualities changed, a process called elemental transmutation. For instance, if Water (Cold and Wet) was heated, it could shed its Cold quality and gain the Hot quality, turning it into Air (Hot and Wet). This system provided a logical explanation for how one substance could visibly change into another.
The Legacy of Aristotelian Physics
The Aristotelian model of matter proved durable due to its logical coherence and alignment with common sensory observation. His system successfully explained natural phenomena, such as heavy things falling (Earth seeking its natural place) or smoke rising (Fire seeking its natural place). It offered a framework for understanding the physical world that matched everyday experience.
During the Middle Ages, scholars like Thomas Aquinas integrated Aristotle’s writings into Christian theology, cementing his physics as the accepted view. This synthesis ensured the dominance of the four-element theory for nearly 2,000 years. Consequently, the concept of chemical atomism remained a minority view until the Scientific Revolution of the 17th century.