Words that are assigned to the same part of speech generally display similar behavior in terms of syntax—they play similar roles within the grammatical structure of sentences—and sometimes in terms of morphology, in that they undergo inflection for similar properties. Commonly listed English parts of speech are noun, verb, adjective, adverb, pronoun, preposition, conjunction, interjection, and sometimes numeral, article or determiner. Essentially all these word classes exist within all Parts of the speech pdf-European languages, even though articles might sometimes be considered as a part of a noun.
Conversely, Hungarian completely lacks prepositions and Finnish only has very few of them, in addition to which it also has some postpositions. Hungarian is an agglutinative language whereas Finnish is typologically between fusional and agglutinative languages, but both belong to the Uralic language family.
A part of speech—particularly in more modern classifications, which often make more precise distinctions than the traditional scheme does—may also be called a word class, lexical class, or lexical category, although the term lexical category refers in some contexts to a particular type of syntactic category, and may thus exclude parts of speech that are considered to be functional, such as pronouns. The term form class is also used, although this has various conflicting definitions.
Almost all languages have the word classes noun and verb, but beyond these there are significant variations in different languages. This variation in the number of categories and their identifying properties means that analysis needs to be done for each individual language. Nevertheless, the labels for each category are assigned on the basis of universal criteria.
The classification of words into lexical categories is found from the earliest moments in the history of linguistics. It can be seen that these parts of speech are defined by morphological, syntactic and semantic criteria. The Latin names for the parts of speech, from which the corresponding modern English terms derive, were nomen, verbum, participium, pronomen, praepositio, adverbium, conjunctio and interjectio.
This is reflected in the older English terminology noun substantive and noun adjective. Later the adjective became a separate class, and the English word noun came to be applied to substantives only.
Works of English grammar generally follow the pattern of the European tradition as described above, except that participles are now usually regarded as forms of verbs rather than as a separate part of speech. Some modern classifications define further classes in addition to these. For discussion see the sections below.