Exemplification entails explaining something through the citing of an example. Prototypical exemplifying constructions consist of two units: the first unit is a general description of the phenomenon in question, and the second a specific example of it. The present paper explores the origin and development of for example and for instance as markers used to link these two typical units in exemplification. Several British English corpora will be used as sources of data. The acquisition of the exemplifying function has led to the fossilization of for+instance/example as invariable prepositional phrases, which may suggest that they have undergone a process of grammaticalization (cf. Heine et al. 1991; Hopper and Traugott 2003; Fischer et al. 2004). Material from the corpora will be analysed as a means of discovering whether the form and function of these two phrases has been stable over time, or if they have shown variations at some point in the history of the language, such as the use of prepositions other than for or the insertion of a determiner between the preposition and the substantive. Cases of exemplification in which the first unit is omitted will also be considered.