Occam's razor
![Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica (1660). The motions of the sun, moon and other solar system planets can be calculated using a geocentric model (the earth is at the centre) or using a heliocentric model (the sun is at the centre). Both work, but the geocentric system requires many more assumptions than the heliocentric system, which has only seven. This was pointed out in a preface to Copernicus' first edition of De revolutionibus orbium coelestium.](/Images/godic/202501/23/Heliocentric0306.jpg")
![Possible explanations can become needlessly complex. It is coherent, for instance, to add the involvement of leprechauns to any explanation, but Occam's razor would prevent such additions unless they were necessary.](/Images/godic/202501/23/Leprechaun_or_Clurichaun0306.png")
Occam's razor (also written as Ockham's razor, and lex parsimoniae in Latin, which means law of parsimony) is a problem-solving principle attributed to William of Ockham (c. 1287–1347), who was an English Franciscan friar and scholastic philosopher and theologian. The principle can be interpreted as stating Among competing hypotheses, the one with the fewest assumptions should be selected.