Aristotle: The Philosopher as Scientist

Ancient Greece was the birthplace of many scientific fields.  The men we have to thank for this are the Greek philosophers, who while not scientists in our sense, were frequently exploring scientific ideas.  The greatest of these 'scientific' philosophers was arguably Aristotle, whose interest in the natural world would, more than any other individual in antiquity, shape the development of scientific thought.  While we now know most of his ideas were false, this episode sets out to defend his legacy and place it in the context of the scientific work which would for the next millenia develop under his influence. In this episode we explore Aristotle's contribution in many fields including his theory of matter, theory of motion and his zoology.  

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Transcript

Hello and Welcome to the Complete History of Science!

Series 2, Episode 1 – Aristotle: The Philosopher as Scientist.

I wanted to begin our second series by welcoming back everyone who listened to the first series of the podcast, far more people listened than I ever expected, and I am very grateful.  However, if you’re new to the podcast then thank you for downloading, and I hope you join us on this journey through the history of science.  

In the first series we started by exploring the question of where science began, taking a tour through arguably the first science, astronomy, before stopping at the point where it began to stall during the Greco-Roman period.

However, astronomy was far from the only science practiced in the ancient world. It is in my opinion a failing that too many popular histories of science that they start with the history of astronomy, before quickly jumping forward to the scientific revolution.  This is unfortunate as it leaves out many of the diverse, interesting and ultimately important scientific ideas which were taking root in this period.

When I called this podcast the complete history of science, I was serious, because my aim is to give a complete overview of the history of scientific ideas, at least, until we reach the modern age.  In the second series then we’ll explore the many other scientific fields which originated in the ancient world.  This will mean starting in the world of ancient Greece, because it was undoubtedly here where the foundations of science were laid.  The men responsible for this genesis however, were primarily Philosophers, who, while not scientists in our sense, were often developing scientific ideas, ideas which would become the basis for the scientific thought which followed. So today, it makes sense to start with the ancient philosopher who arguably had the greatest impact in the history of science, the man we know as Aristotle.

Aristotle was born in the Greek region of Macedonia, and worked in Athens around the 4th century B.C. We know from the last series the central role that Aristotle played in the development of astronomy. However, his scientific work was much broader, and he contributed significantly to many scientific disciplines.  Indeed, as we continue this series there will be few areas in which Aristotle’s name won’t be mentioned, and his ideas are the ground zero in many scientific fields.  

In the long term, most of Aristotle’s ideas proved to be wrong, however, I still believe that it is key that we cover him in detail, because he provides necessary context for later ideas. It’s a mistake in my opinion, not to take Aristotle’s work seriously, or to relegate him to a footnote in the stories of, for example, Galileo and Newton. And that’s because I don’t think we can fully appreciate Galileo and Newton’s scientific contribution unless we first understand Aristotle’s.  We’ll find this repeatedly in many scientific fields, where it’s in fact Aristotle’s ideas which provide the background against which new ideas can take shape. In many areas, Aristotle was there first, and understanding his theories are key to understanding how so much science originated and developed. 

Perhaps part of the reason Aristotle is so readily dismissed is the sharp distinction we make in our minds between philosophy and science.  However, this distinction wouldn’t have been meaningful in the ancient world.  While we nowadays think of ‘philosophers’ as primarily interested in reason, metaphysics, or ethics, many of earliest philosophers were actually interested in the workings of nature. 

This conception of philosophy, as disinterested in the physical world, however, was largely due to the work of another ancient philosopher.  Plato was an older contemporary and some would say teacher of Aristotle, who worked alongside him in Athens.   He wrote widely on many areas of philosophy, however, central to his work, is a rejection of experience and observation as reliable methods for gaining knowledge.  Plato believed that our senses and our perceptions were faulty, and hence give us an unreliable account of the world.  While there is of course some merit to the argument, Plato reached the extreme conclusion that this means we should completely reject observation as a means to acquire knowledge, and instead rely solely on abstract reason.  

As his student, it may be expected that Aristotle would have adopted this view.  However, Aristotle was an extremely well read and original thinker, and largely rejected this position in favour of a more nuanced position.  Aristotle didn’t dismiss reason as a tool, but argued that observation must be the starting point in any attempt to acquire knowledge. Part of the importance of Aristotle in the history of science then goes beyond any specific idea or theory, because his work would provide the intellectual heft which would defend observation as a solid basis for producing knowledge.  

Aristotle wasn’t the first philosopher to defend this position but was instead the last and perhaps the greatest in a line of so philosophers known as the physiologoi.  The earliest of these thinkers was Thales of Miletus, a philosopher born in the 6th century B.C.  His belief was that water was the primary substance of all matter and used this idea as a basis to try to explain various phenomena.  A tradition of philosophers followed Thales.  They had a diverse range of ideas but were united in attempting to explain phenomena as being caused by materials.  They meant this quite literally, so Thales believed water was the main cause of all phenomena, whereas Heraclitus believed it was fire, and Anaximenes believed it was air.  Of course, the ideas of these physiologoi, now seem at best fanciful, and at worst incredibly retrograde.  However, it’s not the details of these claims which have value.  These thinkers were an important steppingstone in the development of science because in contrast to most prehistoric cultures, they sought to explain phenomena in terms of natural causes.  

To illustrate the difference in this new philosophical thought, an interesting comparison can be made between Thales and the earlier writer Hesiod.  In his poetry, Hesiod described the origin of earthquakes as the consequence of Zeus’s wrath.  Conversely Thales explanation of earthquakes was that they were the result of waves lashing the Earth, which he believed was adrift on an immense body of water.  The importance of the physiologoi instead lies in the fact that they attempted to give natural explanations of phenomena, which were, by extension open to criticism.  This in turn meant also that their ideas needed to be defended, and were open to vigorous debate.

Indeed the ideas of the physiologoi are largely known to us through the critiques which Aristotle made of them.  His work often builds on and fine tunes the work of his predecessors, synthesising their ideas into his larger philosophical system.  While I think it’s fair to dismiss the ideas of the early physiologoi, Aristotle’s ideas are far more sophisticated and deserve attention because they were so important in the development of later science.

As we have mentioned the physiologoi were preoccupied with the idea that matter was fundamental in explaining physical phenomena.  While Aristotle largely disagreed with the physiologoi on the details, he did give primacy to the idea that matter was central to explaining everyday phenomena and this formed the basis of his most famous theory. Aristotle posited that there were four primary elements, Earth, Water, Fire and Air.  He considered all the matter which we observe to therefore be some combination or mixture of these four underlying substances.  This theory wasn’t fully original to Aristotle but had been developed from the work of another earlier philosopher, Empedocles.  

Empedocles was, like Aristotle and the physiologoi, interested in the natural world.  His major contribution in the history of science was to demonstrate that air is in fact a substance, rather than just empty space.  In one of the earliest recorded scientific demonstrations, he used device known as a Clepsydra, or water clock.  This is a vessel with two holes, one in the bottom and one in the top.  By placing the bottom hole of the vessel under water, Empedocles observed that the vessel filled up. However, if he put his finger over the top hole, then the water did not enter the hole at the bottom. Empedocles deduced that the air was preventing the water entering, and hence must have some substantial material form, like water or earth.  Empedocles then suggested that these three elements, together with fire make up all underlying physical matter. 

Aristotle refined Empedocles theory of matter by suggesting that each element also has two corresponding properties being either, hot or cold, and, wet or dry.  So for example, fire was hot and dry, while water was wet and cold.  However, these properties aren’t immutable and can undergo change.  For example, if you heat water it goes from cold to hot and hence becomes air.  Aristotle therefore gives us one of the earliest attempts to explain a change of state.

Aristotle’s theory of matter wasn’t unique in the ancient world but was also proposed in opposition to another school of philosophers, the atomists.  Of these atomists Democritus was arguably the most important.  Democritus had argued that all matter was made of tiny particles which he called atoms.  He arrived at this theory through the observation that everyday matter was divisible.  You can for example, use a hammer to break a rock into smaller pieces.  Keep hitting it and the pieces will keep getting smaller and smaller. He reasoned however, that this was only possible up to a point and eventually we would reach the smallest of possible particles, which were the indivisible atoms. In Democritus’s theory atoms could differ in size, shape, order and position, but otherwise they were the only really existing objects, and moved through an empty void or vacuum.  This may seem a remarkably prescient theory, but it would not be influential as Aristotle’s, at least in the short to medium term.  

Aristotle was firmly opposed to atomism and spent great energy arguing against it.  He was especially contemptuous of the idea of the void between atoms.  Instead he argued that space is full, and matter stretches continuously across all space, what is sometimes called the plenum.  Aristotle appealed to a combination of observation and deduction in order to argue this.  For example, Aristotle observed that an object falling through a medium will have a speed which is dependent on the density of that medium.  Specifically, the greater the density, the less speed the object falls with.  He reasoned that if an object then moves through a void, it would move at an infinite speed, an obvious absurdity to Aristotle, as it would imply the object would be in two places at once.  

Such arguments of course wouldn’t withstand scrutiny today, but the success of Aristotle’s theory compared to atomic theory, was because at the time they gave at least a coherent explanation to questions posed by the ancient Greeks. This argument also demonstrates how Aristotle’s theories of matter formed a part of his much larger system, which Aristotle used to explain a great range of phenomena. So for instance, Aristotle used his theory of matter to provide one of the first serious attempts to explain motion.  

Aristotle considered Earth and water the heavier elements, and they were supposed to move directly downwards, while air and fire were lighter elements, and hence naturally move upwards.  Aristotle of course realised that this couldn’t possibly always be true so differentiated between this natural motion of the elements and artificial motion, which only exists under coercion by an outside force.  To give an example, a stone, which would be considered Earth, should fall directly downwards, but if you throw it, you provide an external force which propels it forward.  

However, this explanation of motion left Aristotle with several questions to answer. Aristotle had implied a force was always required to act on an object for it to continue to move, and while this may appeal to our common-sense notions of how forces work if we scrutinise the idea slightly we run into problems.

Let’s say you throw a stone, why does it continue to move in the direction you throw it?  After all, when it leaves your hand you no longer provide any external force.  

However, Aristotle was ready with an answer.  He suggests after you throw the stone, there was still a force acting upon it provided by the surrounding air, which continues to propel the stone forward.  This again makes some sense within Aristotle’s larger system, because the air is a continuous medium which acts upon the stone after it has left your hand.

Aristotle expanded this idea to explain how objects move through resistive mediums.  He hypothesised that the motion through a medium was determined by the density of that medium, coming to the sensible suggestion that an object moves more slowly through a denser medium owing to a greater resistive force.  

It is worth noting at this point that Aristotle’s theories weren’t explicitly mathematical.  As we know from our account of ancient astronomy, science at this time largely lacked any quantitative basis.  Aristotle also lacked more sophisticated notions, such as speed or velocity, and discussed motion purely in terms of distances travelled and time taken. However, he did make arguments from which mathematical statements could be inferred.  

Most famously Aristotle suggested that the speed which an object falls is directly proportional to its weight, and hence an object twice as heavy should fall to the ground twice as quickly.  This idea would go on to have a perhaps surprisingly long history, given that it should have been immediately apparent, even in Aristotle’s time, that it was wrong.  

Because again, while it may appeal to common sense that heavier objects fall faster, the implication was that an object say 100 times heavier, must fall 100 times faster.  And this could be demonstrated to be false by even the most rudimentary experiment.  

However, this raises an important issue we should address, because despite Aristotle’s appeal to empiricism and observation, he never conducted experiments.  Instead, Aristotle believed that it was important to observe the world without imposing any artificial constraints.  The great historian of science David Lindberg presents Aristotle’s line of thought, and the argument goes something like this.

If we want to discover the nature of a thing, we should observe it in its natural unobstructed state.  If we instead impose constraints or observe an object in an artificial experiment, we corrupt the behaviour we hope to observe.  

This is of course antithetical to the scientific method which would develop in the 17th century.  Eventually when Aristotle’s ideas would be unseated, his theories of motion would be one of the first battlegrounds, and one where experiment would ultimately lead to his ideas being rejected. 

However, Aristotle’s observational approach still has much value, and this would especially be the case in the field to which he has the greatest claim to have personally begun, that is zoology.  While there had been some prior interest in animals, Aristotle was the first person to take seriously the study of animals as an intellectual endeavour.  This is reflected in the volume of extant work, because before there are only scattered references to animals in Greek philosophy, but in Aristotle we have at least three major works dedicated to both the physiology and the behaviour, of large swaths of the animal kingdom.  

Aristotle gathered masses of data to this end, and his writings contains descriptions of over 500 animals.  Aristotle must have made some of these observations personally, and he seems especially familiar with many species of fish.  This is perhaps not surprising given the proximity of Greece to the Mediterranean Sea.  More unexpected however, is that he also gave various descriptions of exotic animals, native to North Africa and Central Asia.  Some of this information undoubtedly came from travellers and reports which Aristotle gathered. EXAMPLES?  Aristotle, however, is no Pliny the Elder, and should be commended for his scepticism for not necessarily accepting all reports that come his way.  Even when he does report hearsay, he is careful to preface it with a disclaimer.

He also clearly relies on his own observations to disprove some of the more wild claims made by his predecessors.  The historian Herodotus had claimed for example, that Hyenas are hermaphrodites, and self-reproduce.  Aristotle, by contrast demonstrates his commitment to observation, and made careful examination of the Hyena’s genitals, demonstrating that though similar, the male and female, have their own reproductive organs.  

This is but one example where we can be fairly sure that Aristotle seems to have personally made the observations he reports.  Incredibly and somewhat inexplicably, Aristotle manages to include descriptions of exotic animals that he couldn’t have possibly obtained from reports of travellers.  For example, its plausible he could have perhaps gathered from others that Elephants have a large body, a trunk and tusks, but how could he also have known they don’t have a gall bladder, or that the Elephants liver is roughly four times the size of an ox.  Its speculated that Aristotle must have dissected or witnessed the dissection of an elephant, though how this would have been feasible in ancient Greece is unknown.  One speculative suggestion is that he may have had some unknown collaborator, possibly his nephew Callisthenes, who while a part of Alexander the Great’s expeditions into Africa and Asia, sent an Elephant home to Greece.

That Aristotle carried did carry out dissections himself is almost certain because he made several discoveries on the internal workings of animals.  Most celebrated of these discoveries, he described the reproductive system of the dogfish, discovering that somewhat similar to mammals, they give birth to their young alive, what we would know call ovoviviparous.  This wasn’t reconfirmed until the 19th century when Johannes Muller performed a similar dissection.  

We shoud, perhaps however, be careful not to overstate Aristotle’s scientific objectivity, he was also liable to speculation and whimsy amongst his more celebrated successes.  For example,  Aristotle can’t help but anthropomorphise his descriptions of some animal behaviours, so the Ox is sluggish and good tempered, the snake treacherous and mean, horses intelligent and the fox crafty and mischievous.  

Likewise his biggest and most influential mistake in zoology was in endorsing the idea of spontaneous generation.  Unable to observe the mating behaviours and reproduction cycles of certain animals, Aristotle suggested that these animals were instead generated spontaneously from non-living matter.  So for example snails supposedly grew spontaneously in muddy ground, whereas scallops and clams would develop from sand.  This theory would again have a long history, and wouldn’t be disproved until Louis Pasteur demonstrated the converse in the 19th century.  

Nevertheless, Aristotle’s also made one huge positive contributions to the broader development of biology, because he created the first system of classification for living things. His system is based on a nested hierarchy and bears more than a passing resemblance to what we would recognise from Linnaean systems.  Aristotle separated animals into two major classes, blooded and bloodless.  Within the class of blooded animals he included mammals, birds and fish.  He then further divided these subclasses into the various species, or ‘gene’.  Aristotle’s system was based on observations of similarities of traits between animals but he also recognised that it was difficult to make classifications of some species within this system.   EXAMPLE? Overall he takes a largely pragmatic approach to the problem,  and frequently settles upon what is mostly true.  This problem of how to group classifications would endure and not finally be resolved until it was eventually settled in modern classifications systems based on genetics. 

This early classification system is largely forgotten, but I think that it is amongst Aristotle’s greatest achievements.  And I think there is no better compliment in than to it than that made by Darwin, who famously remarked that Curvier and Linnaeus were mere schoolboys next to old Aristotle.  

So we will leave Aristotle here.  However, as I hinted at that the beginning of the episode, we’ll not really be leaving Aristotle.  He will rear his head again repeatedly throughout this second series, and long into the future, in virtually every field of science we dare to cover.    

Nevertheless, next time we will return with an episode on another of the great scientific figures of antiquity, Archimedes.