109. Use the comma to set off any sentence element that is placed out of its natural order.
If it is possible, he will do it.
To most people, this will seem absurd.
110. Use the comma to set off slightly parenthetical remarks that are thrown into the sentence. If the break is very marked, use the dash or parenthesis.
That, if you will permit me to explain, cannot be done without permission from the police.
Two men, Chase and Arnold, were injured.
He, himself, said it.
111. Use the comma to set off explanatory or non-restrictive clauses, but not to set off restrictive clauses. (See §§ 25 and 26.)
Mr. Gardner, who has been working in the bank, sang at the church.
But: The Mr. Gardner whom you know is his brother.