"Aristotle... distinguished four sorts of explanatory factor... and in later centuries these came to be known as his 'four causes'. The name is unfortunate, since nowadays we usually restrict the term 'cause' to one of his four types... they would have been better called his 'four becauses'—since he was concerned to distinguish, not the different varieties of cause and effect, but rather the different senses in which the question 'Why?' can be asked... [W]e could give four different answers, whose relevance would depend on our precise interpretation of the question. We could refer to: (i) The material constitution... or 'From what?'... (ii) The form, essence, or 'What was it?'... (iii) The precipitating cause or 'By What?'... (iv) The end [destination or purpose], or 'In aid of what?'... These four types of explanation are not necessarily rivals. ...all four types can frequently be cited without inconsistency. Indeed, apart from a few phenomena... which have no function and so 'just happen', Aristotle thought all natural events called for explanation in all four ways."