  There are four types of proper name according to Priscian, the Encyclopedist Isidore of Seville, and medieval grammarians, namely praenomen, nomen, cognomen, and agnomen. For Isidore of Seville, the nomen was the name of the gens or clan, a group of people with a common ancestor, but for Priscian, Peter Helias and the modistic grammarians, such as Thomas of Erfurt, the nomen was the most properly proper name, that which signified an individual “in an absolute way under the properties which gave him his individuality” as Thomas put it. The praenomen distinguished between people of the same family. The cognomen was the family name, and the agnomen was a name, such as ‘Africanus’, given in honour of some achievement, especially military. Peter Helias asked whether the four types of name had the same signification, and whether the cognomen was a common noun. In his reply, he made an explicit distinction between a principal signification which is unique and a secondary signification. The cognomen principally signifies an individual quality, but secondarily signifies the common quality of belonging to a certain family group. He added that this distinction applied to all four types of proper name, and so they all have the same principal signification when used of one person. This reinforces the claim that proper names are not equivalent to a set of common characteristics, and cannot be defined. 