Aristotle's four causes/explanations
Theory derived from the work of Greek philosopher Aristotle (384-322 BC). 'Cause' is a misleading, but traditional, translation of a word meaning 'factor responsible', or perhaps 'explanatory factor'.
The 'four causes' provide answers to four questions one might ask about something, for example, a man:
'What is it made from?' 'Flesh and so on' (material cause);
'What is its form or essence?' 'A two-legged creature capable of reason (say)', (formal cause);
'What produced it?' 'The father (on Aristotle's biology)' (efficient cause);
'For what purpose?' 'To fulfill the function of a man (roughly meaning 'to live a life in accordance with reason') (final cause).
The doctrine, or parts of it, can then be extended in various ways (in particular to cover events and states as well as objects), and undergoes various complications in the process; but its primary application is to objects, especially biological objects and artifacts.
The four causes, especially the first two, are closely linked to Aristotle's important dichotomy between matter and form (hylomorphism).
Aristotle, Physics, book 2