With subordination you use words or word groups to distinguish the main ideas, or in other words, to indicate that some ideas in a sentence are less important than the idea in the main clause. In the following sentence, it is difficult to tell what is most important:
*Computer prices have dropped, and production costs have dropped more slowly, and computer manufacturers have had to contend with shrinking profits.
The following revision places the point of the sentence (shrinking profits) in the main clause and reduces the rest of the information to a modifier (underlined).
Because production costs have dropped more slowly than prices, computer manufacturers have had to contend with shrinking profits.
No rules can specify what information in a sentence you should make primary and what you should subordinate; the decision will depend on your meaning. But, in general, you should consider using subordinate structures for details of time, cause, condition, concession, purpose and identification (size, location, and the like).
Because Jones had been without work for months, he was having trouble paying his bills.
The UN will have to take action soon, for there is no individual country that is prepared to get its hands dirty.
A clause with for is always separated from the host clause by a comma. You may also come across sentences consisting only of a for-clause; these are not seen as fragments because for is a coordinating conjunction like and and but. Dictionaries tend to give for as the standard translation of Dutch want, but for is significanly different from want in that it is very much more formal.
Arbitration boards have clearly been a great success, in that the number of working days lost to strikes has fallen by 50% since the boards were introduced.
The force of in that here might be paraphrased as 'and my evidence for claiming this is as follows'. Note that a clause with in that follows its host clause but cannot precede it.
Although the horse looked gentle, it proved hard to manage.
While some countries did agree to NATO intervention, others were strongly against it. Voting in the south was brisk, whereas in the north it got off to a slow start.
Whenever forecasters predict a mild winter, farmers hope for an early spring.
Congress passed new immigration laws so that many Vietnamese refugees could enter the United States
After the mine explosion killed six workers, the owners adopted safety measures.