The traditional focuses of sociology include social stratification, social class, social mobility, religion, secularization, law, sexuality and deviance.
These were called calceus mulleus, and the name may have been shortened to mules by English speakers. Hence the primary difference between mules and clogs in early days was that clogs were likely to be worn by working people, and mules were fancier and favored by the aristocracy.
Mules have the same usage as donkeys do. They do not allow the use of Horse Armor. They can carry items for the player. A mule can only hold one Chest, even though it appears to have two (one on each side). A chest is simply equipped by placing a chest on the mule by right clicking.