Linguistic typology is a subfield of linguistics that studies and classifies languages according to their structural and functional features. Its aim is to describe and explain the common properties and the structural diversity of the world's languages. It includes three subdisciplines: qualitative typology, which deals with the issue of comparing languages and within-language variance; quantitative typology, which deals with the distribution of structural patterns in the world’s languages; and theoretical typology, which explains these distributions.