If you are going to compare languages, it helps to start with something that you are confident you can find in all languages. Take for example signs or words for mother and father. If we add other family relationships to this category ─ son, grandmother, aunt, brother-in-law, cousin ─ we are defining the category of kinship terminology. Comparative typological studies of kinship terminology have discovered that languages have labels for some but not all family relationships. And the probability that a specific kin relationship has a label is predictable based on the other kinship terms in the language. For example, all languages have a core set of kinship terms ─ like mother and father. By contrast, terms for less central category members are often built up from the core terms ─ like mother-in-law and step-father. If we compare languages across the world, we can ask what kinship relationships are typically expressed with core terminology, and what relationships are expressed by modifying the core terminology.