Comma before introductory sentence elements
[The following is from Hulon Willis. Basic Usage, Vocabulary, and Composition (NY: Holt, Rinehart and Winston, 1969).]
Use a comma to set off an introductory sentence element if the element is long or if a comma is necessary to avoid ambiguity. The more careful a writer is, the more likely he is to use commas to set off initial sentence elements. But when clarity is not affected, you may include or omit such commas according to your own preference.
All careful writers, however, follow the above rule when clarity is at stake. For example, only a careless writer would omit commas in the following sentences:
As we were about to leave the restaurant manager hastened to apologize to us.
Above the buzzards circled ominously.
As I mentioned the rules may occasionally be broken.
Omission of the commas in these sentences results in ambiguity, for without a comma to make him pause, a reader first assumes that restaurant, buzzards, and rules are objects of the preceding verbs or preposition rather than subjects of the following clauses.
Initial verbal phrases are usually set off by commas because of the distinct voice pause between such a phrase and the following clause:
Not realizing the danger, the platoon crept forward.
Failing that, we must resort to force.
To avoid ambiguity, a writer must punctuate carefully.
Introductory exclamations and introductory words of assent or doubt are also set off by commas:
Why, we were old friends in optometry school.
Yes, we feel that he is due compensatory damages.
Well, perhaps he intended no disrespect.
Insert commas where needed in the following sentences. Decide which sentences would be correct either with or without a comma.
1. From the beginning of recorded history man has pondered his relationship to the universe.
2. As the car started about a dozen raced in front of it.
3. Not having a copy of the book I was unable to verify the quotation.
4. As I started to run a way to escape occurred to me.
5. As I expected the visitor turned out to be a relative.
6. If an astrologer is right one out of ten times there are people who will trust him in everything.
7. Considering everything we did very well in our fund drive.
8. Of course our first performance was rather rough and unprofessional.
9. As I had already determined to go would mean to risk our lives.
10. Naturally we were glad that justice triumphed.
11. As I was saying the Lord's Prayer is a comfort because of the beauty of its style.
12. Whenever one inch of rain falls within two hours all the streets are flooded two feet deep.
13. To give an estimate about four hundred members are expected to come.
14. Why I would be able to ski that well myself.
15. In spite of his judgment that decision was devastating.
16. To tell the truth about twenty of the students had not studied at all.
17. Although dangerous tigers generally will avoid men.
18. In order to win he bought fifty votes from skid row bums.
19. Although Truthful James is a famous character his creator is unknown.
20. As I investigated the police were already on their way to the scene of the crime.