were On Generation and Corruption and Physical Discourse, which concentrated upon ideas concerning matter, form, motion, time and the heavenly and earthly realms.
To Aristotle, the earthly realm was composed of a blend of the four elements which, if left to settle, would form layers: water falling through air (or air moving up through water, as do bubbles), solid earth falling through water and air, and fire existing in the top layer because it moves up through air. Using this model, Aristotle would have explained the fall of an apple as being due to the earthy and watery parts of the solid apple trying to find their natural place in the universe, falling through air to reach the ground. As well as popularising the idea of the four elements, Aristotle also pioneered the concept of the Unmoved Mover – the name he gave to the omnipotent being who maintained the movement of the heavens, keeping the Sun and the planets travelling around the Earth.
Aristotle’s work was encyclopedic in range, and he wrote on almost all subjects known at the time, covering logic, philosophy, biology, astronomy and physics. His strongest subjects were logic and, of the sciences, biology; his weakest was physics. Most significant for how Aristotle arrived at many of his scientific ideas was his creation of syllogistic logic: the principle that a conclusion can be reached as a logical consequence of two preceding premisses. An example of this is the collection of statements ‘All elephants are animals; all animals are living things; therefore all elephants are living things.’
Syllogisms are powerful tools in the study of logic, and were used as a fundamental mathematical procedure until the nineteenth century, when they were superseded by more versatile ideas, but their use is a rather superficial way to conduct science, because syllogistic logic does not contain an element of experiment: syllogisms consist merely of two statements and a conclusion based upon superficial observation or deductive reasoning.
Plato, Aristotle’s teacher (and the man who established the school at the Academy in Athens which lasted nine centuries), actively disliked experiment and so it was never established as a guiding principle for Greek natural philosophy. Instead, Aristotle and the generations of Greek thinkers who followed him created a rigid set of rules based upon syllogistic logic only, producing a distorted picture of reality. But, because of Aristotle’s stature, this limited approach became endowed with an aura of infallibility which persisted until the beginning of the modern era. The historian Charles Singer has said of this unfortunate process:
The whole theory of science was so interpreted, and the whole of logic was so constructed, as to lead up to the ideal of demonstrative science [i.e. conclusions reached through reasoning alone], which in its turn rested on a false analogy which assimilated it to the dialectics of proof. Does not this mistake go far to account for the neglect of experience and the unprogressiveness of science for nearly 2,000 years after Aristotle?1
In the same vein, the writer and historian Sir William Dampier pointed out that:
Aristotle, while dealing skilfully with the theory of the passage from particular instances to general propositions, in practice often failed lamentably. Taking the available facts, he would rush at once to the wildest generalisations. Naturally he failed. Enough facts were not available, and there was no adequate scientific background into which they could be fitted.2
The modern scientific method involves reasoning and experiment. To give a simple example: early on in a scientific investigation an idea is postulated – often based upon an inspired insight. This is then developed into a tentative hypothesis by means of pure reasoning – a process called the inductive method. The practical consequences of this hypothesis must then be deduced mathematically and the idea is tested experimentally. If there are discrepancies between the hypothesis and the experimental results or observations, the hypothesis must be altered and the experiments be repeated until there is either agreement between reasoning and observation or the original idea is discarded. If the reasoning and the practical verification eventually agree, the hypothesis is promoted to the status of a theory. This can then be used to attempt to explain a more generalised scenario than the original concept and may hold for many years. But, crucially, it is still never considered to be the only theory that could fit the facts, and good science allows for new ideas to be introduced that may destroy the old theory or demand radical changes.*
Aristotle’s dominance left no room for alternative ideas. Democritus, the father of the atomic theory, believed that ‘According to convention there is a sweet and a bitter, a hot and a cold, and according to convention there is colour. In truth there are atoms and void.’ Aristotle dismissed this notion by relying upon syllogisms that were founded upon inadequate knowledge. For example, he claimed that, if the atomic theory were true, matter would be heavy by nature and nothing would be light enough in itself to rise. A large mass of air or fire would then be heavier than a small mass of earth or water, so the earth or water would not sink (or the air and fire rise) and therefore the elements would not find their natural positions. This argument illustrates how Aristotle was not approaching the problem in the way a modern objective scientist would – he was not able to consider questioning his own cherished beliefs even when presented with a strong alternative theory.
Aristotle’s dogma became almost a religion among his followers, and his teachings were passed on to future generations virtually unquestioned, misguiding future thinkers and leading science along a partially blind alley for several hundred years without interruption.
By the time of Aristotle’s death, in 322 BC, the Egyptian city of Alexandria was about to emerge as the intellectual centre of the world. At its heart was the great library which is said to have contained all human knowledge in an estimated 400,000 volumes and scrolls. From Alexandria, learning spread eastward with the conquests of Alexander the Great and west into Europe, where Greek philosophy, science and literature acted as the foundation for Roman culture. This was especially true of science: the Roman era could boast many great intellects – Pliny, who lived during the first century AD and wrote a thirty-seven-volume treatise, Naturalis Historia, and Plutarch, a thinker of the following generation, to name only two. But these men did little original science and concentrated on refining and clarifying Greek teachings passed on to them.
Of the Greek science that survived through to the early Roman era, the work of Aristotle, Plato, Archimedes and Pythagoras was best preserved, although the ideas of Democritus were championed by the Roman philosopher Lucretius in his poem De Natura Rerum. By the time Roman power was melting away and the library at Alexandria was decimated at the hands of the Christian bishop Theophilus around AD 390 (it was later sacked a second time by the Arabs during the seventh century), Aristotle’s work was becoming unfashionable.
The reason for this lies in a shift from pure intellectual inquiry to a distrust of any learning beyond theological exegesis: this plunged most of civilisation into what has become known as the Dark Ages. In this era, as the Roman Empire was in rapid decline, education and learning became dominated by religious fanaticism. The disciples of this new movement, the Stoics, believed in the supreme importance of pure spirit over material existence and therefore shunned learning about the physical world as an end in itself. To them, Aristotle’s work was too mechanistic, too embedded in physical reality.* Instead, the musings of Plato held much greater relevance and were perfectly in tune with the new obsession with religious meaning.
Plato had taught an anthropocentric view of reality in which everything was created and carefully controlled by a supreme being who held the interests of humanity paramount. For Plato, the movements of the planets were there simply to enable the marking of time, and he viewed the cosmos as a living organism with a body, a soul and reason. He also saw numerical relevance and meaning in all natural processes, and because of this he placed great importance upon mathematics. However, he abhorred experimental
