Participle clauses
Ramesh Chandra Sharma from India writes:
  What is the difference in meaning between these two sentences:
Seeing an accident ahead, I stopped my car.
Having seen an accident ahead, I stopped my car.
 
 
Roger Woodham replies:
 
 
 
 There is not very much difference in meaning between these two pairs of sentences. Sometimes we can use an -ing or past participle clause with similar meanings, as here, although use of the past participle form emphasises that the first action has been completed before the second action begins. Thus, we could paraphrase these two sentences as follows:
 
Having seen an accident ahead, I stopped my car. I noticed that there had been an accident ahead and stopped my car.

Seeing an accident ahead, I stopped my car. When I saw the accident ahead, I stopped my car.
 
In general, we tend not to use participle clauses so much in speech. They are too formal. In speech we would probably say:
 
I saw an accident ahead, so I stopped my car.
 
  However, in written English participial clauses can be very useful. As you can see from the examples above, when the subject in the participle clause is the same as the participle in the main clause, they enable us to say the same thing, but with fewer words. 
 
 
participial clauses = adverbial clauses
  Participial clauses often express condition, reason, cause, result or time in a similar way to full adverbial clauses, only more economically. Compare the following:
 
Used sparingly, this face cream should last you until Christmas. If you use it sparingly, this face cream should last you until Christmas.
Having taken the wrong train, I found myself in Bath, not Bristol. Because I had taken the wrong train, I found myself in Bath, not Bristol.
Passing the theatre on my right, I walked up the steps and could see all the lights on the Thames ahead of me. After I had passed the theatre on my right, I walked up the steps and could see all the lights on the Thames ahead of me.  
  Note from the above examples that the -ing form participle is used to talk about past, as well as present events, e.g.:
 
Talking to you I always feel that my problems will be solved.
By talking to you, I always feel that my problems will be solved.
 
 
participle clauses following conjunctions and prepositions
  Participle clauses, with -ing particularly, can be used after various conjunctions and prepositions, such as: when, while, before, after, on, without, instead of. Note the following examples:
 
Remember to take all your belongings with you when leaving the train.
I sprained my ankle while playing tennis.
Before entering the mosque you must take off your shoes.
After taking everything into consideration, we decided to sell the house.
After having driven 300 miles across country, I arrived to find the house had been sold.
On hearing that my sister was planning to marry him, I decided to leave the flat to her.
Without wanting to seem rude, I must tell you that you are ungrateful.
Instead of listening to my advice, she walked out without saying goodbye.
 
 
  Note from the above examples that the participle clause normally, but not invariably, comes in front of the main clause.
 
 
 
negative participle clauses
  Negative participle clauses are also possible, in which case not normally comes before the -ing form or past participle:
 
Not having had a shower for two days, I was desperate to get to the bathroom.
Whilst not wishing to appear impolite, I must ask you to leave so that I can make a private telephone call.
 
 
having been + past participle
  Note that this passive structure can also be used in participle clauses as an alternative to a since-clause:
 
Having been invited to the party by Prince William himself, we could hardly refuse to go. ( = Since we had been invited?
Having been deprived of food for over twenty days, the castaway was fed intravenously at first.
Having been unemployed for over two years, I found it difficult to get work.
 
 
    
An accident