6.2.4 Movement to tense and I
Suppose that, like the negative element, the adverb likes to follow the finite tense and precede the verb. However, unlike the negative it is not rigid about this. Specifically, when the verb and the inflection are in one place, it is impossible for the adverb to be between them. Thus a choice must be made: put the adverb above the tense, or put it below the verb. It seems that the restriction on adverbs preceding verbs is the stronger, so the adverb will be adjoined higher than the I position. The position it is actually adjoined to is the I', which we will see is a position where the sentential adverb may appear: