Government and Binding Theory/Split INFL Hypothesis
In languages like English or French, tense and agreement are often represented by a single morpheme. Consider:
(1a) He drinks milk.
(1b) Ils sautaient.
In (1), -s indicates both third-person singular singular and present, while in (2), -aient indicates third-person plural and imperfect (past tense + imperfective aspect).
However, lot all languages are like this. Some languages have no agreement at all, such as Mandarin (Putonghua):
(2) Wo/ni/ta/women/nimen/tamen qu-le caiguan.
(I/you-sing/(s)he/we/you-pl./they go-asp. restaurant)
Others have two separate morphemes for tense and aspect, like Finnish:
In the Finnish example, -i is the imperfect suffix and n is the person suffix.
To account for multiple inflectional morphemes, the Split INFL Hypothesis has been proposed. It suggests that IPs are actually split into agreement phrases (AgrP) and tense phrases (TP).
As we have seen in the Finnish example above, the tense morpheme is attached before the person morpheme. This suggests that the tense is closer to the verb than the person, i.e. this structure:
The Agr and T morphemes move and stick to the VP later, as we will soon see.
Jean-Yves Pollock famously proposed the Split INFL Hypothesis in 1989 through a comparison of French and English syntax. As this is just a beginner's book, we will offer a simplified account of his proposal without going into marginal cases and exceptions involving auxiliary verbs. Refer to the following sentences:
(4a) Je mange toujours des pommes.
(I eat always art. apples)
(4b) I always eat apples.
(4c) Je ne mange pas de pommes.
(I ne eat not art. apples)
(4d) I do not eat apples.
This gives us the (tentative) analysis below, in which English finite inflections move to V position stick there, whereas French verbs move to I position and stick there, indicating a parametric difference (we omitted the ne, as in colloquial French, to keep things simple):
Is this analysis sufficient? Obviously, it isn't, or it wouldn't have led Pollock to the hypothesis. This was the reason:
(5a) Ne pas manger de pommes
(ne not to-eat art. apples)
(5b) Not to eat apples
Interestingly, in French infinitives, the verb is to the left of not, not much different from English. What's going on? One could potentially suggest that French verbs don't move out of the VP in infinitives:
Yet leads to another problem:
(5c) Ne pas manger toujours de pommes
(ne not to-eat always art. apples)
We're now cornered. It's a 'damned if you do, damned if you don't' situation: If the V moves, we cannot accommodate pas, which is left of the verb, and if the I moves, we cannot accommodate the adverb, which is right of the verb. There has to be something between pas and the adverb, but what is it? Pollock suggests that there are actually three layers of stuff involved: the agreement phrase (AgrP), the negative phrase (NegP), consisting of the ne head and the pas specifier, and the tense phrase (TP). The details of how he came to this conclusion are too complex to be presented here, but the following diagram should show the relationship between the phrases:
If we look carefully at French, it may in fact appear that the tense and agreement in French aren't a single morpheme after all. Refer to the following:
The above data suggest that -s, -s, -t, ons, ez and ent are actually typical person suffixes of French verbs, while ai and i act as imperfect suffixes. In fact, as we can see from prendre, the tense morpheme precedes the person morpheme, just like in Finnish, suggesting that AgrP comes before TP!