The characteristic function of AdvPs is to modify the verb. In general they are adjuncts, but we have noted that they qualify as complements with the few verbs like treat where they are obligatory. AdvPs also occur as complement to the verb be in its specifying sense (§5.5.1):
- She writes exceptionally clearly. [adjunct]
- They treat us quite abominably. [complement of treat]
- The only way to do it is very, very slowly. [complement of specifying be]
Why 'slowly' is used, not 'slow'? Is it because 'the way' is a kind of manner? Accordingly, in 'Tomorrow is too early' 'early' may have the part of speech of 'adverb' : 'Tomorrow'is a kind of time.
So,are the limitations 'manner' or 'time'? If not, we could also say 'You are so beautifully'.