1. Summary of Reduction of Adverb Clauses

2. An adverb clause can be changed to a modifying phrase only when the subject of the adverb clause and the subject of the main clause are the same.

3. 1- Subordinate conjunction + subject + be + verb
Keep the subordinate conjunction
Drop: subject + be
While I was talking to Sam, I noticed an old friend.
While I was talking to Sam, I noticed an old friend.

4. 2- Subordinate conjonction + subject + verb
Keep the subordinate conjunction
Drop the subject
Change the verb to –ing form (gerund)
After I ate breakfast, I went to work.
After I ate eating breakfast, I went to work.

5. 3- Because / As / Since* (cause and effect conjunctions)
Drop the subordinate conjunction
Drop the subject
Change the verb to –ing form (gerund)
Because Sue needed to read the book, she borrowed a copy from the library.
Because Sue needed Needing to read the book, she Sue borrowed a copy from the library.

6. 3- Because / As / Since* (cause and effect conjunctions)
Having + past participle gives the meaning not only of "because” but also of “before.”
Because I have seen that movie before, I didn’t want to go again.
Having seen that movie before, I didn’t want to go again.

7. 3- Because / As / Since* (cause and effect conjunctions)
A form of be in the adverb clause may be changed to being. The use of being makes the cause-and-effect relationship clear.
Because she was unable to afford a car, she bought a bicycle.
Being unable to afford a car, she bought a bicycle.
Unable to afford a car, she bought a bicycle.

8. 4- When 1. You can either follow the general rule:
When I arrived to school, I started reviewing for the exam.
When arriving to school, I started reviewing for the exam.
2. Or:
Replace when with upon
Drop the subject
Change the verb to –ing form (gerund)
When I arrived Upon arriving to school, I started reviewing for the exam.