used in negative statement to describe a situation that has existed up to this point or up to the present time; "So far he hasn't called"; "the sun isn't up yet"
used after a superlative; "this is the best so far"; "the largest drug bust yet"
conduct an inquiry or investigation of; "The district attorney's office investigated reports of possible irregularities"; "inquire into the disappearance of the rich old lady"
investigate scientifically; "Let's investigate the syntax of Chinese"