A study is made of the history of the type and related concepts, from Greek Antiquity up to the present. It is demonstrated that the type-concept of eighteenth century biology was based on Leibniz's concept of substantial form, and was not related to a Platonic Idea, whilst it is now generally understood in the sense of model or norm. In the present paper, a type-concept is developed which includes ontogenetic and phylogenetic time and various evolutionary mechanisms. This type can serve (...) as a model of the evolutionary potentialities of a taxon, and as a standard of higher classification. All classifications based on the same archetype, whether typological, numerical or phylogenetic, will be comparable, although not necessarily identical. (shrink)