Study materials
Two sentences with the same content. The second is three words shorter, and that is how books are written.
While she was walking home, she met Tom.
Walking home, she met Tom.
The phrase removes the conjunction, the subject and the form of be. But the compactness has to be paid for with care: the phrase has no subject of its own and borrows one from the main clause.
Simultaneity, cause, passive
The phrase replaces a whole clause. Its form depends on what you are showing.
| What the phrase shows | Form | Example |
|---|---|---|
| a simultaneous action | ing | Walking home, I met Tom. |
| a cause | ing | Feeling tired, she left early. |
| the subject undergoes the action | third form | Written in 1890, the book still sells. |
Opening the door, she saw the letter.
Built in the 1970s, the bridge needs repair.
The choice between the ing and the third form is made exactly as in reduced modifiers: does the subject act or undergo the action.
The main rule: a shared subject
The phrase has no subject of its own, so it borrows one from the main clause. If the subjects differ, the sentence falls apart.
Walking home, the rain started.
Walking home, I got caught in the rain.
The test takes a second. Read the phrase and then the subject of the main clause. If they do not fit together, the phrase cannot be used.
The comma is compulsory
When the phrase opens the sentence, a comma always follows it. It shows the reader where the adverbial ended and the main idea began.
Feeling tired, she left early.
Not knowing the address, we asked a passer-by.
The negative is built with not in front of the ing form, as in the second example.
The mistakes everyone makes
The first is using the phrase with different subjects.
Opening the door, the phone rang. → As I opened the door, the phone rang.
The second is taking an ing where the subject is passive.
Building in 1890, the bridge still stands. → Built in 1890, the bridge still stands.
The third is losing the comma.
Feeling tired she left early. → Feeling tired, she left early.
All three are caught by one test. Read the phrase together with the subject of the main clause and ask whether that subject really performs the action.
Try it right now
Take two of your own sentences with when or since and rewrite them in English as phrases.
Then check each one: is the subject the same in both halves?