OG #21 (verbal review purple book)
It is possible that Native Americans have migrated to the Western Hemisphere over a bridge of land that once existed between Siberia and Alaska.
OG criticizes the use of the present perfect. It recommends the use of the simple past. I’m OK with that for the sentence above because the Native American migration has clearly stopped.
But take the following:
(1) It is possible that the disease has spread through food contamination.
(2) It is possible that the disease spread through food contamination.
In (1) the disease still persists.
In (2) we don't know if the disease still persists.
But both look OK to me, unless I am missing something.
(1) It is possible that he has committed the murder.
(2) It is possible that he committed the murder
Same question. Pick (1) or (2) ? Both look OK.
An additional confusion arises since the present perfect can be used for an action that completed at an indefinite time in the past.
I have attended college.
[I attend no more].
Here its the opposite. The present perfect seems correct even thought the action has ceased.
I am sorry if I have confused everyone, but please help me in choosing b/w simple past and present perfect.