Occam's Razor

The English philosopher, William of Occam (1300-1349) propounded Occam's Razor:

Entia non sunt multiplicanda praeter necessitatem.

(Latin for "Entities should not be multiplied more than necessary"). That is, the fewer assumptions an explanation of a phenomenon depends on, the better it is.

For example, some claim that God caused himself to exist and also caused the universe to exist - he was the "first cause" - whereas Occam's Razor suggests that if one accepts the possibility of something causing itself then it is better to assume that it was the universe that caused itself rather than God because this explanation involves fewer entities.

The negation of Occam's Razor would suggest that an arbitrarily complex explanation is just as good as the simplest one. (E.g. God and his cat created a robot called Sparky who built the universe from parts bought from a shop in another dimension).