It is well known that northern Middle English had a reduced set of agreement endings on its verbs (Brunner 1938, Mossé 1968, Roberts 1993). Indeed, in the present tense in all persons and numbers but the first singular, which had -e, the ending was -(e)s; and in Scotland even the first person singular was occasionally -s (Brunner 1938). This system represents a simplification compared to the Old English and southern Middle English pattern, which had -e, -(e)s(t), -(e)th in the three persons of the singular and -(a)th (-(e)n in the Midlands) in all persons of the plural. Since the Old Norse system of endings was richer even than Old English, it has not been clear where the northern simplification came from. However, if we follow modern sociolinguistic approaches to the relationship between language change and second-language acquisition (Appel & Muysken 1987), we are led to suggest that the simplification is the result of imperfect second-language learning of English by the Norse invaders of the 9th to 11th centuries. The appearance of Norse-origin grammatical markers in the northern dialect (see section 2 above) is clear evidence that second-language learners with an imperfect command of English grammar were a sufficiently large fraction of the population in the North to pass on their mixed language to succeeding generations, what is traditionally known as a substratum effect. One feature of imperfect learning, as is well known, is the imperfect acquisition of inflectional endings; and the northern Middle English endings seem to have originated in this way. The simple replacement of the marked anterior fricative // by the unmarked anterior fricative /s/ is nearly all that is needed to transform the Old English paradigm into the northern Middle English one, and there is evidence of confusion between the two sounds in 9th century Northumbrian (that is, the northern dialect of Old English). Scribes, in addition to writing /s/ for //, occasionally wrote a hypercorrect // for /s/ in verbal endings (Brunner 1965). We propose, therefore, that imperfect learning in a language contact situation was responsible for this morphological change (see Kroch et al. 1995 for further discussion).
Now we have the basis for understanding the origin of the northern V2 grammar. According to the most straightforward interpretation of the idea that V-to-I movement depends on rich agreement, the northern system of endings does not make enough distinctions to support movement (Platzack & Holmberg 1989, Roberts 1993, Rohrbacher 1994); if there is no V-to-I movement, it is clear why the northern dialect must be a CP-V2 language. With the verb not appearing in I-zero, IP could not be the locus where the V2 constraint (see section 4 above) was satisfied, since no Spec-head relationship between topic and verb could be established in overt syntax. Therefore, the reduction of the verbal agreement system would force the reanalysis of an IP-V2 grammar into a CP-V2 one.
There is, however, one substantial obstacle to the scenario we have sketched. As Roberts (1993) points out, sentences like (22) indicate that, contrary to our hypothesis, northern Middle English did exhibit V-to-I movement:
Since the negation in (22) is in a relative clause (not a domain for CP-recursion), the order of tensed verb and `not' must be due to movement of the verb to a lower functional head than C-zero; that is, to I-zero under the phrase structure we have been assuming. Not only is the word order in (22) possible, it is obligatory for all verbs, as one would expect if it reflected V-to-I movement. Further effects of this movement are exemplified in a sentence like (23), in which the order of pronoun object and `not' reflect Mainland Scandinavian-type object shift of pronominal objects, which is also obligatory:
These data make it clear that the northern dialect does not share the apparent lack of verb movement characteristic of modern Mainland Scandinavian, despite its relatively impoverished verbal inflections (see Roberts 1993 for further discussion).
If we accept the conclusion that northern Middle English had verb movement, we cannot maintain our scenario for the history of the dialect in the simple form outlined above. There is, however, a modified version that can be maintained, provided that we adopt the split-INFL hypothesis of Pollock (1989). We assume, as is usual, that AGR-S is the highest projection below COMP and that T(ense) is the next highest. Let us further suppose (following a suggestion by Naess cited in Thráinsson 1994) that the modern Mainland Scandinavian languages have verb movement to T, though not to AGR-S. This proposal has the virtue of maintaining a strict relationship between overt morphology and verb movement. Since Scandinavian has overt tense marking in both the present and the past, it has verb movement to T. By the same logic, so does northern Middle English; and if so, then raising only as far as T could explain why we see movement across negation and object shift. If northern Middle English `not' is an adverb adjoining to VP, as it certainly was in Old and earliest Middle English (see Frisch 1994 for detailed discussion), then verb movement to T will produce the attested order of V-finite > `not'. Further, if object shift is movement to any functional specifier above VP (see note ), the order pro-object > `not' found in examples like (23) will also be correctly generated. The remaining question is why the order of `not' and tensed verb should be different in northern Middle English than in modern Mainland Scandinavian, given that we take the verb movement facts to be the same in the two cases. But the answer here is straightforward: Northern Middle English inherited the Old English double negative construction `ne ...\ not', in which `ne' is the negative head and `not' is a VP-adjoined adverb, as Frisch shows. Hence, we expect to find `not' below and to the right of T. In modern Mainland Scandinavian, on the other hand, there is no counterpart to `ne', so that the single negative `inte/ikke' must be either a negative head or the specifier of NegP, which is located above T in both English and Scandinavian. Therefore, movement of the verb out of VP to T does not change its relative order with respect to negation.
Using a split INFL forces us to reformulate slightly our account of the role of the V2 constraint in the reanalysis in the northern dialect. We have argued that the constraint is met in Old English by a surface Spec-head agreement relation between the trace of the fronted topic in Spec,IP and the verb in I-zero; and this relationship requires overt verb movement to I-zero. Once INFL has been split, we must ask again where the V2 constraint will be satisfied. The obvious answer is AGR-S; and if that is the locus of the constraint, our analysis of the northern dialect remains viable, since we claim that the verb in the northern dialect does not move as high as that position. If, however, the constraint could be met at the level of T, our analysis would fail, since we have claimed that the verb in the northern dialect does move to T. Notice, however, that using T as the locus of the constraint implies empty expletive incorporation into T to free up Spec,TP as an intermediate landing site for the topic. But for conceptual reasons such incorporation is not possible. Expletive incorporation must entail the merger of the expletive, a pronominal, with the agreement features of a verbal functional head; and the whole point of the split-INFL analysis is to put these features in a different functional head from the one that bears tense.