Pidgins are not fully developed languages in that they do not have deeply formed complex grammars and they have limited vocabularies, limited usually by the context in which and purpose for which they develop. Pidgins develop when two or more groups of people with separate and distinct mutually unintelligible languages are thrust together or voluntarily come together for various benefits and intentionally or unconsciously blend their languages to form a new mode of communication that shares components and features of two or more languages in order to facilitate a mutual end or an end imposed by one group upon the other group(s).
A pidgin does not replace or compete with the native language or vernacular as it is task- or situation-specific, thus speakers continue to use their native language for all other communication. While a pidgin doesn't usually become a native language--meaning that new generations aren't usually reared with a pidgin as the language of the home and that a pidgin is too restricted in form to qualify for a full language--when it does happen that the pidgin becomes pervasive, research has shown that within about one generation definitive steps toward grammar development are advanced within the pidgin and a creole is born out of a pidgin. The transition from pidgin to creole occurred when the Haitian-French pidgin grew to become the Haitian creole of today that incorporates French lexical base with grammatical structure from substrate African languages and has an expanded and functional grammar.
While pidgins can become creoles, not all pidgins do advance to become creoles, and creoles are not of necessity the product of pidgins. The monogenetic theory of creole development hypothesizes that pidgins and creoles are derived from a common base language (e.g., the French of the Haitian pidgin/creole). However the polygenic theory of creole development theorizes that pidgins and creoles may develop independently of each other, without a common base language uniting the one or more other languages, though exception is left in the theory for creoles that clearly have replaced the originating pidgin.
Creoles arising from pidgins are of particular linguistic interest because they each follow a similar path of grammar expansion. Pidgins, as noted, are simplistic communication tools that rely mostly on nouns and verb and adjectives to get main, large points across, such as would be minimally needed in commerce or in the management of manual labor forces, hence the reason for pidgins being classified in the category of lingua franca (language of mutual communication), although it must be noted not all linguas franca are pidgins, such as is the case in South Africa where the lingua franca is English.