[...] the most fundamental conceptual basis of classification is that of the expression of fundamental syntactic relations as such versus their expression in necessary combination with notions of a concrete order. [...] There are languages [...] in which syntactic relations are expressed purely, without admixture of implications of a nonrelational sort. We may speak therefore of pure relational languages as contrasted with mixed relational languages. Most of the languages with which we are familiar belong to the latter category.
- Sapir (1933a), a pag.21