Plato & Aristotle A* grade summary notes


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Plato’s rationalism: theory of forms & Allegory of cave

  • Rationalism: the view that knowledge can only be gained through pure reasoning – a priori. 
  • Cave allegory (inc. the sun represents the form of the good)
  • Knowledge cannot be gained from the senses (a posteriori) – because experience is just shadows on the wall of the cave.
  • Theory of forms: the things we see are particular imperfect representations of the true reality which is the world of perfect forms.
  • E.g. when looking at a beautiful sunset – we are looking at the form of beauty, but because our minds are trapped in ignorance, we see a particular beautiful thing which will fade and change. We do not see the reality – the perfect unchanging form of beauty.
  • The only solution is to turn to a priori reasoning.


  • Aristotle’s rejection of Plato’s rationalism
  • There is no empirical evidence for the forms
  • However – Plato wouldn’t care about this criticism – he thinks evidence (which comes from experience) is just shadows on the wall of the cave – so Plato thinks it’s good there is no evidence for the forms!
  • Aristotle has a better upgraded critique of Plato – he says we can gain knowledge from experience/evidence – through studying the causal processes responsible for the change we observe.
  • Aristotle’s theory led to modern science which has successfully gained knowledge and manipulated reality.
  • This makes the theory of forms an unnecessary hypothesis. 
  • So Aristotle isn’t just saying there’s no evidence for the forms – he’s saying Plato is wrong to disregard the value of evidence.

The hierarchy of forms & form of the good

  • The highest form is the form of the good. It’s represented by the sun in the cave allegory.
  • The sun illuminates the world and allows life in the world to exist.
  • Similarly, the form of the good allows us to know the other forms and is also responsible for their existence.
  • Below the form of the good there are high forms like beauty, justice and truth.
  • Below those high forms are mathematical and geometric forms.
  • Below those are the forms of the objects we experience – like the form of treeness or catness or tableness.
  • Knowing the form of the good makes someone perfectly moral.


  • Criticism of the form of the good
  • Aristotle points out that virtue is required to do good, not merely knowing what goodness is.
  • To add to Aristotle: history has never shown us a perfectly moral person.
  • Plato is being optimistic or just inventing the form of the good because he wanted philosophers to rule society.
  • Nietzsche called the form of the good a ‘dangerous error’ and claimed philosophers tend to invent ideas to justify their emotional prejudices, such as a desire for power.
  • Furthermore, Aristotle adds that there cannot be one unified form of the good which captures all the diverse forms of goodness in this world.
  • E.g. in military strategy ‘good’ is efficiently killing people
  • But, in medicine ‘good’ is efficiently keeping people alive

Aristotle’s four causes 

  • Aristotle thinks we can gain knowledge from experience (a view called empiricism).
  • We can analyse the causal processes responsible for the change/motion that we experience.
  • material – what something’s made of – e.g. the ‘wood’ of a chair
  • formal – a thing’s essence or defining characteristic, – e.g. the shape of a chair
  • efficient – what brought it into being – e.g. a carpenter 
  • final – end goal of the thing telos – e.g. for a chair, to be sat on
  • This is an early version of the scientific method. A scientist could explain that if you add the efficient cause of fire to a chair , then because of its material structure of wood the result will be ashes.
  • Aristotle concludes we can gain knowledge from experience by understanding causation.


  • Modern science’s rejection of final causation (telos/purpose)  
  • Modern science only believes in what can be observed through sense experience. It believes the universe is made of atoms and forces like gravity. So, there is no room for purpose (telos) on this modern scientific view. Purpose is therefore just in our minds.
  • Science can explain the change we observe without purpose – so purpose is an unnecessary concept. There is no purpose.
  • Example of a chair – a chair is just made of atoms. We might think it has a purpose and treat it as if it has a purpose – but it doesn’t objectively have a purpose. 
  • We give things a purpose in our mind – but it doesn’t actually have an objective purpose in reality. Purpose is socially constructed.
  • So, Aristotle’s idea of ‘final causation’ is unscientific.

Defence of Aristotle’s method

  • However – although final causation is unscientific, nonetheless modern science would still accept material and efficient causation. So, Aristotle’s theory is not totally wrong.
  • Furthermore, modern science is actually using Aristotle’s method of gaining knowledge from experience. So that method is still valid, even if in Aristotle’s time, because of his limited access to technology and evidence, he got some things wrong.

Aristotle’s prime mover and how it follows from the four causes

  • Aristotle’s argument for the prime mover: 
  • Aristotle noticed that movement runs out – a ball will stop rolling for example.
  • He looked at the universe and saw that things in the world and the planets and stars were still moving – their motion had not run out. 
  • So – he concluded there must be a prime mover which is causing stars/planets to continue moving.
  • The prime mover is not the efficient cause of the universe – it doesn’t push objects into motion. It creates motion because objects are attracted to its perfection. 
  • The prime mover is the final cause of the universe.
  • This prime mover is a pure mind eternally contemplating itself – unchanging and attracting everything in the universe towards it, thereby causing the motion and change we experience.


  • Newton’s rejection of Aristotle’s basis for the prime mover
  • Newton proved that Aristotle was wrong to think that motion runs out. Actually, motion (kinetic energy) just transfers into another type of energy. 
  • If you throw a ball in outer space it will just continue moving potentially forever. 
  • So, the stars/planets don’t need some special explanation like a prime mover to explain why they continue to move.

Defence of Aristotle’s method

  • However, although the substance of Aristotle’s claims about reality is not totally correct, nonetheless his empirical method of gaining knowledge about reality from experience still seems to be correct. That is the method Newton himself used.