Aristotle considered at the beginning of his Physics that we can only know something inasmuch as we can explain it, (‘Knowledge is the object of our inquiry, and men do not think they know a thing till they have grasped the ‘why’ of it’). And for Aristotle, the word he used for the ‘why’ of something was aition, which has been translated as cause, although explanation could also be used.
Aristotle draws a distinction between potentiality and actuality. He applies this to the process of change (or motion). Change is simply the process by which an object acquires a new form (very different from Plato’s idea of form). The object has the potentiality to become something different, and change is the actualization of the potential of one form of matter to become another form of matter. For example, the block of marble has the potential to become an actual statue. The statue is latent within the block of marble – the block of marble has the capacity to become a statue.
There are two important things to note: firstly potency and act are distinct; the marble cannot be both a block and the statue at the same time. In another example a piece of wood cannot be both potentially on fire and actually on fire at the same time – so therefore change is this movement between potential and actual.
Secondly, as the object cannot be both simultaneously potential and actual, how does it move from one to the other? Aristotle says it needs an agent to move it, which he called the efficient cause. This must in itself be in a state of actuality, not potentiality, ie. it must exist to be a cause of the change in the object. Eg. you need actual water to effect the change of an acorn into an oak tree. We can see how from this Aristotle got the first two of his causes – there must be matter which undergoes the change from one form to another, so in one sense, if we say ‘what is it?’ of something or ask for an explanation of it we can say what it is made of – eg the statue is made of marble. This would be then the material cause.
But as we have seen this would not be a total explanation of the thing for Aristotle – he would want to know how the statue got its particular form. This ‘how’ as we have seen, Aristotle called the efficient cause. In the case of the statue, the sculptor acted upon the stone with his chisel in order to make the potential statue in the marble an actual statue.
But Aristotle did not believe we could stop with just the material and efficient causes, the what and the how, as you might say. He believed that as the material has undergone a change of form in going from a potential thing to an actual thing, that part of its explanation was what the characteristics of it were. If we were to say to a person ‘what makes you the person you are?’ they would normally not give a straight list of the elements that compose them such as carbon – they would probably talk about their upbringing or give a character trait, such as ‘I’m happy-go-lucky’. Therefore we need to add another cause other than the purely material to get at a full explanation of a thing – we need to talk about its characteristics – eg. a chair is more than just some wood, it is an object with four legs and a space to sit. Aristotle called this the formal cause.
In the statue example the formal cause would be its particular qualities of marble sculpted into the form of a body, head etc. The formal cause of something is the ‘form’ of the thing – the pattern which makes it what it is – in the case of a building it would be the blueprint. This is not as easily understandable as the other causes, and has been seen as slightly controversial. Clearly, though, much debate surrounds the notion of a form and many agree that Aristotle’s notion is no less flawed than Plato’s.
The fourth cause is called the final cause, and comes from the end of a thing, what it is for. This idea of a purposive cause is given by Aristotle because what something’s aim or goal is is also an important part of an explanation of the thing. Aristotle gives the example of the final cause of walking, medicine, purging, surgical instruments etc. as all being for health. For Aristotle the aim of something can be seen as its greatest good, this is brought out in our use of language when we ask of an object “what is it good for?”