REDUCED CLAUSE
Same time
Time clauses with “while” and “when” can be reduced by deleting the subject and “be” verb.
While I was eating dinner, I watched television.
While eating dinner, I watched television.
When you are in Rome, (you) do as the Romans do.
When in Rome, do as the Romans do.
If there is no “be” verb, change the verb in the subordinating clause to its -ing form. Sometimes the subordinator (when or while) can be deleted as well.
When I opened the door, I saw a strange sight.
When opening the door, I saw a strange sight.
Opening the door, I saw a strange sight.
Note: If the subjects are different, you may not reduce the adverbial clause.
While I was taking a shower, my sister called from California.
X While taking a shower, my sister called from California.
Be careful when reducing time clauses that come at the end of sentences.
We saw many beautiful birds while we were fishing in the lake.
We saw many beautiful birds while fishing in the lake.
X We saw many beautiful birds fishing in the lake.
In the last sentence, the meaning is ambiguous: Are we fishing or are the birds fishing?
Different times
After I finished my homework, I went to bed.
After finishing my homework, I went to bed.
After I had finished my homework, I went to bed.
After having finished my homework, I went to bed.
Having finished my homework, I went to bed.
Before he left the dance, Jerry said good-bye to his girlfriend.
Before leaving the dance, Jerry said good-bye to his girlfriend.
Other clauses
Sometimes clauses with because can be reduced.
Because he was a doctor, George knew how to handle the situation.
Being a doctor, George knew how to handle the situation.
As a doctor, George knew how to handle the situation.