What, of what, by what, for what--these Four Causes explain a thing and enable us to understand it scientifically (Aristotle felt Plato's Forms didn't explain enough, and only duplicated one's troubles- in understanding things).
For Aristotle, the ‘form’ of something was not some kind of abstract Ideal, like Plato had believed, but was found within the item itself. Its form was its structure and its characteristics, the ‘form’ of an object can be readily perceived by the senses. Aristotle used the word ‘substance’ in many different ways, making it one of his most difficult concepts, but one of the ways in which he used it to express the material of which things were made. Aristotle also used the word ‘matter’ to mean the stuff of which something was made. He also wondered whether something could have matter but no form, and he concluded that it could. There can be prime matter, or stuff that ahs no particular form, it is not organized into any structure. He also raised the question whether there could be a substance with form but no matter, and he concluded that this is God.
For Aristotle then the essence of an object was not just its material component parts or its particular shape or characteristics; it also had a purpose, a function to perform. When he studied the world and the objects in it he asked what is it for, what purpose does it serve, why is it here at all? It is this fourth, final cause which is the most important, and which in Aristotle’s view gives the best explanation of an object. The fial end, or the purpose, or teleology of a thing, when realized gives that thing its full perfection and reality. The function of a light bulb is the power to give out light. If it should lose this ability and if this could not be restored, then it will no longer be a light bulb. When something is doing what it is meant to, or has developed into whatever it was supposed to develop into, it ahs achieved its goodness. The purpose of the object for Aristotle is part of the object itself, and not something which we might choose or impose on it – it is intrinsic.
“Aristotle was wrong to imagine that everything has a purpose.”
All the different elements of nature have a purpose, according to Aristotle, and nothing is excessive (superfluous). He considers that everything acts or is actualized for an end or a purpose – this is its telos – and this is in some sense its cause. The telos of a pen is to write, the telos of living things is reproduction. By reproducing, individuals can participate in divine immorality of the only sort that is available to it – immortality of the species. Everything has a desire to realize its form and therefore to achieve its purpose – its final cause. He believed that a universe as a whole has a purpose too. However there are many people who would disagree with that statement.
Aristotle criticizes Plato for his belief in the world of Forms when he has no sturdy evidence of their existence. But we could say the same about Aristotle and his theory – he has no solid evidence that this material world is the source of true knowledge. There are other ways from which knowledge could be gained, apart from through sense experience or reason; religious believers might argue that faith and revelations from God are a source of true knowledge.
There are many people who would say that there really is no reason – it’s just there because it is – and that things happen by blind chance. The French writer Albert Camus, for example, described the universe as ‘absurd’ and Satre said that it was ‘gratuitous’; they thought that it was ridiculous to suppose that the universe had any meaning or purpose beyond the simple fact of its existence. Also some people would claim that there are things that don’t have any reason behind their existence.
Aristotle believed that all natural objects either always or usually come into being in a given way but that is not the case with anything that comes to be by chance or spontaneously. If we think that it is not possible for them to happen by accident or spontaneously, then they must happen for a purpose. So, there is purpose in things that come to be and exist by nature. Also mistakes do occur. The literate man will write incorrectly, the doctor will give the wrong dose; so it is clearly possible, too, for mistakes to happen in things that are in accordance with nature and Aristotle didn’t deny that. He tried to show that like man nature was not always perfect. There would be "monsters".
I think that Aristotle was right and that everything does have a purpose but mistakes do happen. The most common argument that is usually brought forward is that what is the purpose of evil? The answer however is very simple if there was no evil how would we know what good is? There are also things in the universe that at this moment you would not know the purpose for like centuries before us people didn’t know what trees were for, but now we know that they are essential as they provide us with oxygen. We obviously don’t have the answer for everything but in the future we probably would be able to find a purpose for most things even insects that you really think are useless.