further explain and shift focus to the information being presented (Mithun 1984). Although incorporation exists in many languages, incorporation is optional and non-obligatory. Incorporation is restricted to certain noun categories; namely on the degree to which they are animate or alive or suppletive forms. If a language participates in productive compounding it does not allow for incorporation. An example of a compounding language is German. Respectively, if a language participates in incorporation it does not allow for productive compounding. The most common type of NI is where the incorporated noun acts as the notional subject of the clause. This can be observed in Onondaga, Southern Tiwa and Koryak. Types of noun incorporation In 1985, Mithun introduced a four type system to define the functionality and progression of noun incorporation in a language. This system is important as many discuss this, and it is widely applied to explain the differences in NI in languages. The four types are: Lexical compounding: involves a verb incorporating a nominal argument. The resulting compound usually describes a noteworthy or recurring activity. The noun in these compounds are not commonly marked for definiteness or number. Manipulation of case roles: The second type uses the same process to manipulate case roles, incorporating the argument into the verb to allow for a new argument to take its place. Manipulation of discourse structure: The third type uses noun incorporation to background old or established information. A speaker might explicitly mention an entity once, for example, and thereafter refer to it using an incorporated verbal compound. This kind of noun incorporation is usually seen in polysynthetic languages. Classificatory Incorporation: The fourth and final type proposed by Mithun involves the development of a set of classificatory compounds, in which verbs are paired with generic nouns to describe properties of an entity, rather than the entity itself. According to Mithun, languages exhibiting any of these types always display all of the lower types as well. This seems to imply a pattern of progression, as Mithun describes in her 1984 paper on the evolution of noun incorporation. It is argued that it is necessary to distinguish at least two types of noun incorporation. Accounts for noun incorporation A large field of inquiry is whether NI is a syntactic process (verb and noun originate in different nodes and come together through syntactic means, a lexical process (word formation rules that apply in the lexicon