The article investigates the linguistic conditions under which future periphrasis emerged in Old Norse (or its predecessor). Old Norse holds a special position within the Germanic branch since it was the first language where a future periphrastic construction was grammaticalized and became the main means of referring to the future, while other old Germanic languages mostly used the present tense in future meaning.
The principal exponent of the Old Norse periphrastic future was the auxiliary verb munu, attested in this function as early as the 9th century. It is argued that it expressed a remarkably nonmodal future and that it had also developed an early epistemic use which is derived from the futural meaning.
This, as well as the morphological development of munu, is indicative of an early origin of the periphrastic future. In order to account for that it is argued, through comparison with other Germanic languages, that Proto-Germanic made use of verbal prefixes (particularly *ga-) to provide present tense forms with perfective aspect, and hence with future meaning.
Since unaccented prefixes were all lost in North Germanic at an early point, future periphrasis with the verb munu started to develop as a reaction to the loss. It is further argued that another unique feature of the Old Norse verbal system, the use of the historical present, is also linked to this process.
The early development of a future periphrastic construction is considered an important syntactic change, setting apart the North Germanic tense system from the West and East Germanic ones.