What do we mean when we say something was caused by something else? This is an important question for scientists as well as philosophers. Causation is a kind of influence where one event helps creates another event. Aristotle believed that causality meant "explanation", and separated "causality" into four causes: material, formal, efficient, and final. Material cause is what an object is made of. Formal cause is the pattern or shape that organizes the matter in the object. Efficient cause is who or what changes and creates the object. The final cause is the reason why that object was created. Most philosophers today are interested in talking about efficient cause.