Plato & Aristotle: ancient philosophical influences


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Heraclitus was an ancient Greek Philosopher who thought that the world we experience is in a state of constant change which he called ‘flux’. He famously said that a person never steps in the same river twice, since both the river and the person change. Plato interpreted Heraclitus as presenting a challenge to the possibility of gaining knowledge. If everything we experience is constantly changing then we can’t have knowledge since as soon as we know something it has changed.

Both Plato and Aristotle are, in very different ways, attempting to respond to this issue raised by Heraclitus.

Plato thinks that the consequence of Heraclitus’ challenge is that true eternal unchanging knowledge cannot be gained empirically, i.e. from a posteriori observation. Plato concludes that we must give up on the attempt to gain knowledge through experience and look to a priori reason alone.

Aristotle thinks that we can understand the causal mechanism responsible for change and thereby gain true knowledge from experience.

Plato’s rationalism: theory of forms & the cave

Since we cannot gain true unchanging knowledge from the everchanging world we experience, Plato thought that we must not be experiencing the world correctly. Our minds are trapped in a state of ignorance, which is why we experience imperfect, transient and everchanging things in the world of appearance. The true reality must be perfect, eternal and unchanging. Plato calls it the world of forms. True knowledge can only be gained from the world of forms.

In the world of appearances everything we experience is a ‘particular’. Particulars are the objects of everyday experience. They are imperfect representations of the form they partake in from which they gain characteristics. When I look at a tree, I am really looking at the perfect, eternal and immutable form of treeness, but because of my ignorance I see a particular tree which is transient and mutable, it will decay and change into something else as it is in a state of flux. If we see a beautiful painting, we are really looking at the form of beauty but as our minds are trapped in a state of ignorance our perception is faulty and so we perceive merely a particular imperfectly beautiful thing.

The tree gets what little shadowy treeness it has by ‘partaking’ in the form of treeness. It’s like looking at an object in a broken mirror and perceiving a visually distorted version of it. In the case of Plato’s form however, we are perceiving the forms through the broken lens of our ignorant minds.

We get knowledge of the world of forms through a priori reason, not a posteriori empirical sense experience, which reveals merely a vague shadow of the real world (of forms).

Plato illustrates this theory with his allegory of the cave.

Plato asks us to imagine some prisoners (us) in a cave (our reality) who cannot move due to being chained (our minds in a state of ignorance).

They can only look in one direction at a wall on which appear shadows (the objects we experience) of real objects moving behind the prisoners that they cannot see. Those shadows are all the prisoners have ever known, and so they develop a language to talk about them as if they were real. One day a prisoner escapes (a Philosopher), is temporarily blinded by the sun (form of the Good), and then sees the real world (world of forms). He returns to the cave to explain the truth to the other prisoners, but they cannot understand him.

Experience involves mere shadows of the real and that is why it cannot give us knowledge. Only a priori reasoning involving understanding of the forms can give us knowledge.

Aristotle’s rejection of Plato’s rationalism & theory of forms

A common reaction to Plato’s theory of forms is that it lacks empirical evidence.

However, Plato would respond that it’s good his theory has no evidence because evidence cannot be trusted as it is merely shadows of the real world of forms that only a priori reason can discover.

To better criticise Plato requires showing that he is wrong to reject evidence. One way of doing that is by showing how empiricism succeeds, by showing that knowledge can successfully be derived from experience

Plato’s theory lacks empirical validity. Aristotle thought that Plato’s theory of forms was an unnecessary hypothesis, because it has no explanatory power regarding our experience. Plato’s forms are unchanging, but therefore cannot explain the change we experience in the world. Aristotle concluded that the forms are “nonsense, and even if they do exist, they are wholly irrelevant”. Plato’s theory of forms lack empirical validity. This is like an early version of Ockham’s razor and is a general principle in empiricist epistemology, that we should not believe explanations that are unnecessarily complicated, such as a world of forms, when we have a simpler theory that works.

Aristotle’s rejection of Plato depends on the success of his empirical theory of the four causes, or at least on the success of the empirical method. It’s only if empiricism is valid that we can discount Plato’s theory as lacking empirical validity. Aristotle creates an empirical theory called the four causes aimed at gaining knowledge from experience.

The form of the Good & the hierarchy of forms

The form of the good is illustrated by Plato in the cave analogy by the sun, in that it both illuminates and allows us to see the world of the forms, and yet also nourishes and is responsible for all the existence of life and all the other forms. This makes it is the highest form.

Understanding the form of the good makes it impossible for you to do wrong and so Plato says a philosopher with that understanding should rule as a ‘philosopher king’.

Below the form of the good are the higher forms like justice and beauty. They are aspects of goodness; they have goodness in them and is their source.

Below higher forms are lower forms, or forms of phenomena that we experience. For example the form of treeness or catness.

Below that are the actual material objects that we then experience images of. The particular trees or cats that are instantiations (examples) of the lower forms.

Criticism of the form of the good. Aristotle disagrees with Plato’s idea that the cause of immorality is ignorance of the good. Aristotle claims that cultivating virtue is a requirement to do good. Merely knowing what is good is not enough to make yourself morally perfect. We could add evidence to Aristotle’s point, that arguably nowhere in human history has a morally perfect person ever existed.

Plato is either being extremely overly optimistic, or he is just inventing ideas that would justify the type of society he wants, which is philosophers being the rulers. Nietzsche called Plato’s form of the good a ‘dangerous error’ and said that philosophers often invent ideas that suit their emotional prejudices, such as desire for power. They then pretend to have figured out their views through logic and reason.

Furthermore, Aristotle thinks the idea of one unified form of the good doesn’t fit with our experience. It’s simple to see how all the instances of tall things could have a single essence of ‘tallness’, but it’s harder to see how that would work for goodness since different instances of goodness are so radically different. For example, the good in military strategy is how to efficiently kill people, whereas the good in medicine is how to keep people alive Aristotle takes this to mean that there cannot be one unified form of ‘goodness’.

The third man argument

This is a criticism of Plato’s theory of forms. Plato claims that if there is a group of things which share characteristics, like a group of trees, then the explanation is that they must all be partaking in a form of treeness. However, Aristotle argues that we then have a new group of things which share characteristics, the trees and the form of treeness, which according to Plato’s logic must therefore have a form in which they partake, yet that simply creates a new group of things which share characteristics which require another form and so on ad infinitum (forever – an infinite regress). This seems to undermine the idea of the forms that there is a particular single form of a quality that explains the multiple particular instances of that quality we experience in the world of appearances.

Plato responds that forms cannot partake of anything but themselves. Since things share characteristics by partaking in a form, yet forms themselves cannot partake in another form, it follows that forms cannot share characteristics with particulars.

The third man argument thus rests on a misunderstanding of the relationship between forms and particulars. The particulars partake in a form because they are imperfect copies of it, but the forms themselves cannot then be grouped with the particulars since they are what the particulars really are. It makes no sense to group some things together with what they really are since that’s not really a group.

Plato therefore successfully counters the third man argument by blocking the attempted first grouping of a form with particulars and thus showing how an infinite regress does not occur.

Plato’s argument from recollection

The argument from recollection is one of Plato’s arguments for the existence of the world of forms and also the existence of the soul.

Plato points out that we somehow do have knowledge of perfect, eternal and unchanging concepts. These include concepts like perfect beauty and justice. We also have perfect mathematical concepts and geometric concepts such as the idea of a perfect circle or two sticks being perfectly ‘equal’ in length. We have never experienced perfect beauty, justice or a perfect circle. So, we must have gained this knowledge a priori. In The Meno Plato tells the story of how Socrates proved that an uneducated slave boy could be prompted by a series of questions and some shapes drawn in the sand to figure out how to solve a geometry question. The slave boy must therefore have been born with geometric concepts.

Plato then seeks to explain how we could have been born with these concepts. His answer is that we must have somehow gained these concepts before we were born. It follows that there must be a part of us (our soul) which existed in a realm where there were perfect forms. In the world of forms there are perfect mathematical forms and perfect forms like the form of beauty and the form of justice.

We are born with a dim recollection of the forms because our soul apprehends them before becoming trapped in this world of appearances. Anamnesis is the process of re-remembering these forms through a posteriori sense experience.

Plato concluded that the source of knowledge must therefore be a priori, making him a rationalist

The consequence is that there must be a world of perfect and unchanging (immutable) forms, which he called the World of Forms. It is not a distant or other world – it is the true reality. What we see (the world of particulars/appearances) is not the true reality. Everything we experience is a vague shadow of what it really is; a perfect form.

P1. We have a concept of perfect justice and beauty and perfect mathematical concepts.
P2. We have never experienced perfect instances of such things.
C1. So, our knowledge of perfect concepts must be innate.
C2. Therefore there must be a world of forms and we must have a soul which gained perfect concepts from it before we were born.

Justice and beauty are subjective. We could deny P1 by arguing that beauty and morality are subjective; in the eye of the beholder. They seem like matters of opinion, not fact. It seems to be culture that determines and conditions what a person finds beautiful or just and as a result, views on what is beautiful or just change over time and differ cross-culturally. So, everyone has a different concept of perfect beauty or justice which makes it not objectively perfect.

Maths is not subjective. Perfect Plato’s examples of perfect circles and the idea of lines that are perfect equal can get around this issue, however. It is much harder to argue that mathematics is subjective.

Hume responds that we can actually create the idea of perfection in our minds even if we have never experienced it. We have take our concept of ‘imperfect’ and simply concieve of its negation: ‘not imperfect’ to gain the concept of ‘perfect’.

Furthermore we could add to Hume’s point that mathematical knowledge could come from experience. The slave boy may not have had any mathematical training, but he had seen shapes of objects in his life – thereby gaining concepts of shape and geometry from experience. This gave him a basic conceptual understanding that Socrates’ questioning brought out and clarified.

Finally, even if Plato was correct that we were born with perfect concepts, it doesn’t mean a soul and world of forms is the only or even best explanation. Evolution could have programmed us to have a sense of morality, beauty and the evolution of intelligence could explain being born with mathematical ability.

Aristotle’s empiricist teleology

The four causes

Even though the world we experience is in a state of flux, we can gain knowledge about it if we analyse and understand the causal process which explains the change that occurs. If an empirical theory like Aristotle’s theory of the four causes is successful, then Plato’s theory is wrong because Plato thought we could not gain knowledge from experience.

Actuality is the way something is in its current state. Potentiality is the way actual things could become given certain conditions. If certain conditions are met, it will change to its potentiality and that will become its actuality. For example, a seed has the potential to become a tree but only if certain conditions are met will that potential become actual. To go from cause to an effect something must change by going through 4 causes. A thing changes towards its telos – the final end towards which something is directed due to its nature.

  • Material cause: what a thing is made of. E.g. the material cause of a chair is whatever it is made from, such as wood or plastic.
  • Formal cause: what the essence or defining characteristic of a thing is. E.g. the formal cause of a chair is its shape.
  • Efficient cause: what brings the being into existence. E.g. the efficient cause of a chair is whoever made it.
  • Final cause – telos (purpose): the end goal of a thing. The final state which a thing is disposed towards by its nature. E.g. the final cause of a chair is to be sat on.

Aristotle thought that all change in the universe can be explained by these four causes, thereby allowing a posteriori knowledge to make sense of the flux. Example of a chair. The change of a piece of wood into a chair involves the four causes.

Aristotle does not reject the idea of form itself, but only the separation of form from things. On Aristotle’s view, a thing’s form or formal cause is its essence; its defining quality that makes it what it is. This also led Aristotle to reject Plato’s mind-body dualism, since the form of a human (rational thought) cannot be separated from their body.

Aristotle went on to argue that the final cause of the universe must be a prime mover.

Purpose is unscientific. Francis Bacon (17th century), called the father of empiricism, was instrumental in influencing the development of modern science. He criticised Aristotle, claiming that final causation (telos/purpose) has no place in empirical science but is a metaphysical issue, since purpose is a divine matter.

Modern science goes even further than Bacon in its rejection of formal and final causation. A deterministic universe operating by the laws of physics seems to be completely without purpose. All supposed telos of an object can be reduced to non-teleological concepts regarding the material structure of an object. This suggests there is no basis for grounding telos in God as Christians like Aquinas did, or in grounding it as a required explanation of change like Aristotle did. Modern science can explain the change and apparent purpose in the world without telos.

For example, Aristotle would regard the telos of a seed as growing into a tree/bush. However, we now understand the seed’s ability to do that as resulting from its material structure, not some notion of a telos.

McGrath points out that modern Christian philosophers (e.g. Swinburne & Polkinghorne) have argued that science is limited and cannot answer all questions. It can tell us the what but not the why. Science can tell us what the universe is like, but it cannot tell us why it is this way, nor why it exists. It cannot answer questions about purpose and therefore cannot be used to disregard the existence of purpose.

Dawkins responds that the ‘why’ question is valid regarding scientific explanation, but when we ask ‘why’ about purpose it becomes ‘a silly question’. Just because a question can be phrased using the English language, that doesn’t make it valid. Dawkins makes an analogy: ‘what is the color of jealousy?’ That question is assuming that jealousy has a color. Dawkins seems to be claiming that questions of purpose also assume that existence or human life has a purpose over and above scientific explanation, but there’s no evidence for that.

Dawkins accepts there may be limits to science and that where the laws of physics came from may be one of them. However he points out that scientists may one day actually solve that problem, but if they don’t, that doesn’t justify a non-scientific explanation of purpose.

At the very least, the current scientific understanding of the universe works without the need for any kind of telos. A century after Bacon, Laplace wrote a book on the workings of the universe, claiming to have ‘no need’ of the hypothesis that there is a God. More recently, Stephen Hawking made the same claim.

Sartre’s critique of telos

Sartre argued that there was no objective telos/purpose because “existence precedes essence” meaning humans exist before they have a defined purpose and so have to subjectively define their purpose for themselves. Sartre’s argument was a psychological one, that people cling to fabricated notions of objective purpose like religion or Aristotle’s ‘final cause/telos’ because they are afraid of not having a purpose, more specifically they are scared of the intensity of the freedom that comes from having to create their own purpose which Sartre thought led to feelings of abandonment (by God/objective reality), anguish (over the weight of being completely responsible for your actions) and despair (over our inability to act exactly as we’d like due to the constraints of the world). It’s much easier to believe in objective purpose than face that existential angst.

Defence against Sartre: As Sartre’s argument is psychological, he does not provide metaphysical grounds for rejecting telos and so is arguably committing the genetic fallacy. The genetic fallacy is assuming that the way in which someone comes up with a theory is relevant to whether it is true or false. Just because people have a psychological need to believe in objective purpose, that doesn’t mean it doesn’t exist.

However, this criticism of Sartre is unsuccessful because it is a misunderstanding of his argument. Sartre’s starting premise is that there is nothing in our experience of our own mind which suggests we have a telos. All that we experience is ‘radical freedom’ – a sense that every choice we make is completely up to us because there is nothing in our experience like God or telos which could influence or guide that choice. So Sartre is using a kind of a posteriori approach like Aristotle but coming to a different conclusion.

Aristotle on form and his understanding of the soul

Form means essence, which is a thing’s defining characteristic. For a chair, its defining characteristic would be its shape, a shape that can be sat on. However, the essence of a human is not merely its shape. Aristotle claimed the defining feature of a human being is the ability to reason. Aristotle claimed that the soul was the formal cause of the body.

Formal causation is unscientific. F. Bacon was called the father of empiricism for establishing the modern scientific method. He claimed that formal causation is a metaphysical matter that was beyond empiricial study. He gave the illustration of the ‘whiteness’ of snow and explained how science could investigate how snow results from air and water, but this only tells us about its efficient cause, not its colour, the form of ‘whiteness’, which is beyond scientific investigation. So Bacon thought that form existed, but Aristotle was wrong to think science could study it it.

Modern science goes much further than Bacon in its rejection of formal causation, arguing that we have no reason to think it exists at all. The idea that colour is a ‘formal cause’ of an object is now much better understood to be a matter of the activity of particles like atoms and photons, which can be fully explained through efficient and material causation. So what Aristotle thought of as ‘form’ actually reduces to material and efficient causation.

For Aristotle, the form of a human is a rational soul, but most neuroscientists would claim that rationality reduces to material brain structure and its physical processes. So again, what Aristotle thought of as ‘form’, actually reduces to material structure. There appears to be no room left in modern science for formal or final causation.

Science cannot currently explain how consciousness or reason reduces to material brain processes, however. The brain is so complicated and while some of it is understood a bit, processes like reason and consciousness have not even begun to be understood. So modern science cannot yet justifiably dismiss Aristotelian soul & form as the explanation of reason.

However, there is scientific evidence at least linking the brain to reason, since if the brain is damaged then reason and other mental faculties can be damaged too. Since there is so much about the brain we don’t understand, it’s more reasonable to think that mental faculties like reason are reducible to the material causation of brain processes in a way we don’t yet understand, rather than requiring some other type of physical explanation such as Aristotelian form since there is no evidence for that.

Aristotle’s theory of the Prime Mover

Aristotle’s argument for the prime mover resulted from applying the four causes to the universe. The Material cause of the universe is determined by the constituent elements of matter and the ether (the space between matter). The Formal cause of the universe is in the essential nature of things, such as the nature of stars to rotate.

The Efficient cause in the universe. Aristotle had a geocentric view of the universe; that the earth was in the centre of it. He thought the movement of the stars moves the ether which moves the rotation of the planets which maintains changes in the planet’s atmosphere, which maintains the processes of change on the earth.

Aristotle observed that if an object is moved, it keeps moving and then stops. He concluded that objects which are moved simply run out of movement after a while and return to what he thought must be the natural state of objects: at rest. He therefore thought that motion (the world of flux) requires explanation. It was this view which led to his inference of the existence of a prime mover of the universe

Aristotle then questions what maintains the motion of the stars, inferring that there must be something moving them which itself must be unmoved. The cause of the motion of the stars and thereby all movement on earth must itself be unmoved, or its movement would require merely another mover. There cannot be an infinite chain of motion as that would never get started.

This prime mover must therefore have been unmoved and therefore cannot change. It is therefore pure actuality. So, it cannot be material since it seems all material things are subject to change. It must be a mind, but arguably it cannot be thinking about anything happening outside itself since such things are subject to change and its thoughts would change if their object changed. So it must be eternally contemplating itself.

The prime mover is that unmoved mover and the final cause of the universe. It is not the efficient cause of the universe, since Aristotle believed the universe was eternal. The Prime Mover is responsible for the everlasting motion and change of the universe. Since it cannot be moved, it cannot change and is thus pure actuality.

The way the prime mover sustains the change in the world must therefore be due to some sort of attraction of the things in this world to it. Things in our universe are attracted to the prime mover in a sort of orbit. That is how the prime mover sustains the pattern of change from actuality to potentiality in our universe. Things move towards their telos (purpose).

Newton challenged Aristotle’s belief that an object which is moved will simply stop moving by itself. Newton claimed instead that when moved, an object will move until met by an equal and opposite reaction. The problem with observing this is that on earth, the strong gravity and effect of friction amounts to an equal and opposite reaction on the movement of an object which causes it to stop. It doesn’t just stop by itself due to rest being its natural state, as Aristotle thought. This means that Aristotle’s inference that the constant motion in the universe must be maintained by something like a prime mover is false.

Newton’s ideas are most clearly illustrated in the example of a vacuum – space. In outer space where there is less gravity and friction, pushing an object in a certain direction will cause it to move in that direction potentially forever, unless it happens to hit another object or is pulled off course by the gravity of something like a planet.

Aristotle only believed in empirical observation, not empirical experiment. For two thousand years people believed Aristotle, until Newton. Aristotle’s views on formal & final causation and the prime mover are considered completely wrong by modern science, as are Plato’s views, so arguably neither are better?

Defence of Aristotle’s a posteriori method: However, while Aristotle was not truly scientific in the modern sense, nonetheless he believed in empirical observation which created the epistemological method which would lead to modern scientific methods and the resulting fuller picture of reality we have today. In fact it was Aristotle’s a posteriori approach involving empirical observation that led to Newton’s discoveries. So Newton only disproved Aristotle’s claims about reality, he did not disprove Aristotle’s a posteriori approach to understanding reality, in fact Newton used a developed form of that himself.

Extra credit:

Plato’s One Over Many argument

This is an argument for the world of forms. Plato points out that we can conceptually divide the world up into categories like tree, table, beauty, justice, etc. We can only categorize things if we can recognize that they share something in common. The fact that we can recognize that all trees (for example) share something in common, shows that there must be an abstract quality of treeness. Since no particular tree is identical to this abstract quality, it must exist separately. Plato doesn’t see how we could recognize a tree unless we already have in our mind a perfect abstract ideal of a tree; an idea of ‘treeness’, with which we can recognize a particular tree due to it being an imperfect representation of treeness. Since the world of appearances is in flux, how is it that we manage to recognize different things through categorisation? Since the river we step into the second time is no longer the same river as the first, it seems impossible to think of the world in an orderly categorized way if all we have to go on is a world of flux. Yet, we do, and therefore we must be born with the concepts of treeness, beauty, etc. So, Plato concludes we must have a dim recollection of the forms of which the particulars in the world of appearances share some dim shadow-like characteristics by which we are able to recognize and categorize them.

Aristotle’s response to Plato’s One Over Many argument. Aristotle does not object to the idea of form itself, but only to the separation of form from things, which Plato’s one over many argument and theory of forms does. On Aristotle’s view, a thing’s form is its essence; its defining quality that makes it what it is. For example, form of a tree would be the quality essential to being a tree. The essential quality of treeness that a tree has cannot possibly be separated from a tree, otherwise it would not be a tree. So, there is no basis for thinking that the form of ‘treeness’ is a separate entity in another realm.

Wittgenstein’s Criticism of the One Over Many argument. Wittgenstein argued that there is no precisely definable form or abstract ideal of a category. He gave an example of a family picture. There are similarities between the members of the family, but it would be absurd to suggest that recognition of that required understanding of or the existence of perfect abstracted form of that family or that there even is such a thing as an abstracted form of that family. Instead, Wittgenstein argued we recognize someone as a member of a family due to their family resemblances. Similarly, we recognize a member of a category as such due to its family resemblances to other things in that category. The world is not a set of definable categories which the human mind can perfectly divide up. It’s not clear where the boundary between tree and bush are for example, in some species. Humans divide the world linguistically and conceptually in a disorganised haphazard way when it is useful for us within our social context, not according to objective categories of reality. The categories are determined by social convention, not objective reality. Categories are not metaphysical, they are conceptual schemes mapped onto a human experience of the world for the purpose of performing a specific function or use. As such, they have indeterminate boundaries and are subject to revision. What someone decides to call a tree might depend on the use for which the category ‘tree’ has in their social environment. There is no perfect form of ‘treeness’.

Quick links

Year 12 philosophy topics:
Plato & Aristotle. Soul, Mind & Body.
Design/Teleological argument. Cosmological argument. Ontological argument.
Religious experience. Problem of evil.

Year 13 philosophy topics:
 Nature & Attributes of God. Religious language. 20th Century philosophy of language.

OCR Ethics
OCR Christianity
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OCR list of possible exam questions