Student or Learner
Could someone explain to me how to use the adverb "quickly" in the following case?
Prehistoric humans must quickly have learnt what could be eaten without danger.
But why not: Prehistoric humans must have learnt quickly what could be eaten without danger.
Or even: Prehistoric humans must have learnt what could be eaten without danger quickly.
***** NOT A TEACHER *****
I definitely cannot answer your excellent questions, but I can give you some food for thought.
1. If I understand my books, your original sentence should probably be written as:
"Prehistoric humans must have quickly learned [learnt] what could be eaten without danger."
a. The rule is: if the adverb modifies the participle, then place it in front of the participle. I think that "quickly" modifies "learned." What do you think?
b. Here are some examples from my books: "It has been confidently asserted." / "It will have been firmly established." / "The company has been competently managed."
2. "He will undoubtedly have had some news by this time."
a. In this case, the adverb does not modify the past participle "had."
b. It modifies "will have had."
c. Therefore, the rule calls for placing the adverb after the first auxiliary ("will").
d. In other words, the sentence means something like: "There is no doubt that he will have had some news by this time."
3. "Michael refused the cake stubbornly." / "Michael stubbornly refused the cake."
a. According to one book, putting the adverb before the verb gives it "more prominence."
4. "The boy ran home quickly."
a. According to another book, putting the adverb at the end means that the adverb is essential (absolutely necessary) to understand the meaning that the writer wants to express. [Note: That book feels that in "The boy quickly ran home," the word "quickly" is not essential.]
Sources: Wilson Follett / Modern American Usage (1980). / Bruce L. Liles, A Basic Grammar of Modern English (1979). / John Clark Jordan, Making Sense of Grammar (1980).