To separate subordinate clauses from the principal clause the following rules on the use of stops are observed.
§ 13. Subject clauses as a rule are not separated from the principal clause by any stop.
What he learned of farming in that week might have been balanced on the
point of a penknife and puffed off. (Galsworthy)
However, a comma is found if the subject clause is of some length and if a subordinate clause is attached to it.
What had saved him from becoming a cross between a lap dog and a little
prig, had been his father’s adoration of his mother. (Galsworthy)
§ 14. Predicative clauses as a rule are not separated from the principal clause by any stop. A comma is often used when they are joined asyndetically.
Ruth’s point of view was that he was doing no more than was right. (London)
My opinion is, she’d come to me. (Weyman)
§ 15. Object clauses are not separated from the principal clause by a stop. If the object clause precedes the principal clause, a comma may or may not be used.
The silence was so long and deep that he looked up, wondering why the Padre
did not speak. (Voynich)
...and what Browning had done for her, Martin decided-he could do for Ruth.
(London)
Attributive clauses.
1. Restrictive relative attributive clauses as a rule are not separated from the principal clause by stops.
You may be sure every smuggler in the Apennines will do for a man who was
in the Savigno revolt what he will not do for us. (Voynich)
2. Non-restrictive relative attributive clauses are as a rule separated from the principal clause by a comma.
Tom presented himself before Aunt Polly, who was sitting by an open
window. (Twain)
I turned hastily round, and found at my elbow a pretty little girl, who begged
to be directed to a certain street at a considerable distance. (Dickens)
3. Continuative attributive clauses are always separated from the principal clause by a comma.
Oliver was frightened at the sight of so many gentlemen, which made him
tremble: and the beadle gave him another tap behind, which made him cry.
(Dickens)
4. Appositive attributive clauses, are never separated from the principal clause by a stop.
The thought that his adored daughter should learn of that old scandal hurt Ms
pride too much. (Galsworthy)
She paused with an uneasy sense that instead of defending Kath she was