A Little History Of Science: ‘The Master of Those Who Know’ Aristotle
All men by nature desire to know,’ said Aristotle. You have probably met someone like this, always keen to learn more. Perhaps you’ve also come across know-it-alls who have lost the curiosity that always remained important to Aristotle. His hopeful view was that people will strive for knowledge about themselves and the world. We know, unfortunately, that this isn’t always the case.
Aristotle spent his whole life learning and teaching. He was born in 384 bc, in Stagira, Thrace (now Khalkidhiki in Greece). He was the son of a doctor, but from the age of about ten, he was looked after and taught by his guardian Proxenus. When he was about seventeen, Aristotle went to Athens to study at Plato’s famous Academy. He stayed there for twenty years. Although Aristotle’s approach to the natural world was completely different from Plato’s, Aristotle was very fond of his teacher and wrote about his work lovingly after Plato’s death in 347 bc. Some say that the history of Western philosophy is a series of footnotes to Plato; what this means is that Plato raised many of the questions that philosophers still think about. What is the nature of beauty? What is truth, or knowledge? How can we be good? How can we best organise our societies? Who makes the rules we live by? What does our experience of the things of the world tell us about what they ‘really’ are?
Aristotle, too, was intrigued by many of these philosophical questions, but he tended to answer them in a way we might call ‘scientific’. He was, like Plato, a philosopher, but he was a natural philosopher, what we are calling a ‘scientist’. The branch of philosophy that most excited him was logic – how we can think more clearly. He was always busy with the world about him, on the ground and in the skies, and with the way natural things change.
Much of what Aristotle wrote has been lost, but we are lucky to have some of his lecture notes. He left Athens after Plato died, probably because he felt unsafe as a foreigner there. He spent some years in the city of Assos (now in Turkey), where he set up a school, married the daughter of the local ruler and, after she died, lived with a slave girl with whom he had a son, Nicomachos. It was here that Aristotle began his biological investigations, which he continued on the island of Lesbos. In 343 bc, Aristotle took a very important job: tutor to Alexander the Great, in Macedonia (now a separate country just north of Greece). He hoped to turn his pupil into a philosophically sensitive ruler; he didn’t succeed, but Alexander came to rule over much of the known world, including Athens, so Aristotle could safely return to that city. Instead of going back to Plato’s Academy, Aristotle founded a new school just outside Athens. It had a public walkway (peripatos in Greek), so Aristotle’s followers became known as Peripatetics, or those constantly moving around: an appropriate name considering how much Aristotle himself moved from place to place. After Alexander’s death, Aristotle lost his support in Athens, so he moved one last time, to Chalcis, in Greece, where he died shortly afterwards.
Aristotle would have been puzzled to be described as a scientist; he was simply a philosopher in the literal meaning of the word: a lover of wisdom. But he spent his life trying to make sense of the world around him, and in ways that we would now describe as scientific. His vision of the earth, its creatures and the heavens around it, influenced our understanding for more than 1,500 years.
Along with Galen, he towered over all other ancient thinkers. He built on what had gone before, of course, but he was no armchair philosopher. He actually engaged with the material world as he attempted to understand it.
We can separate his science into three parts: the living world (plants and animals, including human beings); the nature of change, or movement, much of which is contained in a work of his entitled Physics; and the structure of the heavens, or the relation- ship of the earth to the sun, moon, stars and other heavenly bodies.
Aristotle spent much time studying how plants and animals are put together and how they work. He wanted to know how they develop before birth, hatching, or germination, and then how they grow. He had no microscope, but his eyesight was obviously good.
He described brilliantly the way chicks develop in an egg. After a batch of eggs had been laid, he cracked one each day. The first sign of life he saw was a tiny speck of blood pulsating in what would become the chick’s heart. This convinced him that the heart was the key organ in animals. He believed the heart was the centre of emotion and what we would call mental life. Plato (and the Hippocratics) had located these psychological functions in the brain, and they were correct. Nevertheless, when we are frightened, or nervous, or in love, our hearts beat faster, so Aristotle’s theory was not silly. He attributed the functions of higher animals, such as human beings, to the activities of a ‘soul’, which has various facul- ties, or functions. In humans, there were six main faculties of the soul: nutrition and reproduction, sensation, desire, movement, imagination, and reason.
All living beings have some of these capacities. Plants, for instance, can grow and reproduce; insects such as ants can also move and feel. Other bigger and more intelligent animals acquire more functions, but Aristotle believed that only human beings could reason – that is, they could think, analyse and decide on a course of action. Human beings therefore sat at the top of Aristotle’s scalanaturae (‘scale of nature’, or ‘chain of being’). This was a kind of ladder upon which all living things could be arranged, beginning with simple plants and working upwards. This idea was taken up again and again by different naturalists, people who study nature, especially plants and animals. Look out for it in later chapters.
Aristotle had a good way of working out what is done by the various parts of a plant or animal, such as the leaves, wings, stomach or kidneys. He assumed that the structure of each part was designed with a particular function in mind. Thus, wings were designed for flight, stomachs for the digestion of food, and kidneys for the processing of urine. This kind of reasoning is called teleological: a telos is a final cause, and this way of thinking focuses on what things are like or what they do. Think about a cup, or a pair of shoes. They both have the shape they have because the person who made them had a specific purpose in mind: to hold liquids for drinking, and to protect feet while walking. Teleological reasoning will appear later in the book, not just in explaining why plants or animals have the various parts that they do, but in the wider physical world as well. Plants germinate and animals are born, they grow and then die.
The seasons regularly come and go. If you drop something, it falls to the ground. Aristotle wanted to explain changes like these. Two ideas were very important to him: ‘potentiality’ and ‘actuality’.
Teachers or parents may tell you to reach your potential: that usually means something like getting the best possible marks in a test, or running a race as fast as you can. That is part of Aristotle’s idea, but he saw a different kind of potential in things. In his view, a pile of bricks has the potential to become a house, and a lump of stone has the potential to be a statue. Building and sculpting trans- form these inanimate objects from a kind of potential to a kind of finished thing, or ‘actuality’. Actuality is an end-point of potentiality, when things with potentiality find their ‘natural state’. For example, when things fall, like apples from an apple tree, Aristotle thought that they seek their ‘natural’ state, which is on the earth.
An apple will not suddenly sprout wings and fly, because it and all other things in our world seek the earth, and a flying apple would be very unnatural. That fallen apple may continue to change – it will rot, if no one picks it up and eats it, because that is also part of an apple’s cycle of growth and decay. But just by falling it has achieved a kind of actuality. Even birds return to earth after they soar into the sky.
If the ‘natural’ resting place of things is on the firm earth, what about the moon, the sun, planets and stars? They may be up there, like an apple hanging in a tree, or a boulder on a mountain ledge, but they never come crashing to earth. Good thing, too. Aristotle’s answer was simple. From the moon downwards, change is always happening; this is because the world is composed of the four elements: fire, air, earth and water (and their properties: hot and dry fire, hot and moist air, cold and dry earth, and cold and moist water). But above the moon, things are made instead of a fifth, unchanging element, the quintessence (‘fifth essence’). The heavenly bodies move forever in perfect circular motion. Aristotle’s universe filled a fixed space but not a fixed time. The sun, moon and stars have been moving for all eternity around the earth, which floats at the centre of it all. There is a lovely paradox here, for the earth, the centre, is also the only part of the universe in which change and decay can take place.
What caused all this movement around the earth in the first place? Aristotle was very concerned with cause. He developed a scheme to try to explain causes by breaking them down into four kinds. These were called material, formal, efficient and final causes, and he thought that human activities, as well as what happens in the world, could be broken down and understood this way. Think about making a statue from a lump of stone. The stone itself is the material cause, the matter out of which it is made. The person making the statue arranges things in a certain, formal manner, so that the statue takes shape. The efficient cause is the act of chiselling against the stone to make the shape. The final cause is the idea that the sculptor had in mind – the shape, say, of a dog or horse – which was the plan of the whole activity to begin with.
Science has always dealt with causes. Scientists want to know what happens and why. What causes a cell to start dividing endlessly, with the result that a person develops a cancer? What turns leaves brown, yellow and red in the autumn, when they have been green all summer? Why does bread rise up when you put yeast into it? These and many similar questions can be answered in terms of various ‘causes’. Sometimes the answers are pretty simple; sometimes they are very complicated. Mostly, scientists deal with what Aristotle called efficient causes, but the material and formal causes are also important. Final causes raise a different set of issues. In scientific experiments today, scientists are content with explaining the processes rather than seeking any larger explanation or final cause, which has more to do with religion or philosophy.
Back in the fourth century BC, however, Aristotle believed that these final causes were part of the picture. Looking at the universe as a whole, he argued that there must be some final cause that started off the whole process of movement. He called this the ‘unmoved mover’, and later many religions (Christianity, Judaism and Islam, for example) identified this force with their God. This was one reason why Aristotle continued to be celebrated as such a powerful thinker. He created a world-view that dominated science for almost 2,000 years.