Four Causes and Prime mover – video clip and summary

First, watch the short cartoon overview of the concepts.

Aristotle’s description of the Four Causes is relatively easy to understand, but there are some more difficult details which will separate higher-achieving students from the herd. The following summarises the more complicated elements.

Aristotle is attempting to explain the ontology of the universe (the nature of stuff, or “matter”). Here is a logical progression of his thought process in a simplified format:


  1. The universe is made up of pre-existing matter.
  2. Matter moves from a state of potentiality to actuality.
  3. Something in a state of potentiality cannot move itself into a state of actuality.
  4. The Four Causes are needed to explain the process of “matter” moving from potentiality to actuality (see Metaphysics Book V for more detail).
  5. Aristotle believed there were three substance categories (Metaphysics Book XII).
  6. *Substance categories one and two are subject to the four causes, while substance category three is not.
  7. The Prime Mover is found in substance category three and is required to ensure the “movement” of potentiality to actuality (see step 3) – movement in this sense does not mean physical movement but rather a change of state from potential to actual.
  8. The Prime Mover does not act but draws the rest of the universe towards it by virtue of the fact that it exists in a state of pure actuality. It is impersonal, immanent and necessary in nature, contemplating only itself.

That a final cause may exist among unchangeable entities is shown by the distinction of its meanings. For the final cause is (a) some being for whose good an action is done, and (b) something at which the action aims; and of these the latter exists among unchangeable entities though the former does not. The final cause, then, produces motion as being loved, but all other things move by being moved. Now if something is moved it is capable of being otherwise than as it is. Therefore if its actuality is the primary form of spatial motion, then in so far as it is subject to change, in this respect it is capable of being otherwise – in place, even if not in substance. But since there is something which moves while itself unmoved, existing actually, this can in no way be otherwise than as it is … The first mover, then, exists of necessity; and in so far as it exists by necessity, its mode of being is good, and it is in this sense a first principle. (Metaphysics Book XII Part 7 – Translated by WD Ross – my emphasis.)

*Substance categories

Aristotle describes the different substance categories in Metaphysics Book XII. It is not for the faint of heart. Most of Aristotle’s work is reasonably accessible but this is a particularly difficult passage.

In order for Aristotle’s ideas of the Four Causes to work everything in the universe must be explicable by it. He sets out various substance categories to help him do this.

  • Substance category one is evident or sensible, subject to decay and affected by the four causes. This is by far the most common category and the vast majority of things exist in it: trees, aardvarks, jam, people, marmalade, etc. Note, this is not an exhaustive list!
  • Substance category two is evident or sensible but not subject to decay. This category is also affected by the four causes. Aristotle places the universe and time in this category. This is based on his belief in pre-existing matter. The universe and time are in a constant state of change but will never perish. They are seen as eternal.
  • Substance category three is not subject to the four causes and exists eternally. In this category Aristotle places the prime mover and mathematics (owing to the Ancient Greek’s belief that mathematics was eternal, awaiting discovery).


Good students should be able to make the link between the Four Causes, potentiality and actuality, the substance categories and the role of the Prime Mover in holding all of the other concepts together logically.

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