Morphological typology is a way of classifying the languages of the world (see linguistic typology) that groups languages according to their common morphological structures. The field organizes languages on the basis of how those languages form words by combining morphemes. Analytic languages contain very little inflection, instead relying on features like word order and auxiliary words to convey meaning. Synthetic languages, ones that are not analytic, are divided into two categories: agglutinative and fusional languages. Agglutinative languages rely primarily on discrete particles (prefixes, suffixes, and infixes) for inflection, while fusional languages "fuse" inflectional categories together, often allowing one word ending to contain several categories, such that the original root can be difficult to extract. A further subcategory of agglutinative languages are polysynthetic languages, which take agglutination to a higher level by constructing entire sentences, including nouns, as one word.