+Explanation+.—The subject clause is here an indirect question. See Lesson 74.
5. When letters were first used is not certainly known. 6. "Where is Abel, thy brother?" smote the ears of the guilty Cain. 7. When to quit business and enjoy their wealth is a problem never solved by some.
+Explanation+.—When to quit business and enjoy their wealth is an indirect question. When to quit business = When they are to quit business, or When they ought to quit business. Such constructions may be expanded into clauses, or they may be treated as phrases equivalent to clauses.
The +noun clause+ may be used as +object complement+.
8. Galileo taught that the earth moves.
that
———-
'
earth | ' moves
———|———-
\the |
|
Galileo | taught | / \
=========|==============
|
+Explanation+.—Here the clause introduced by that is used like a noun as the object complement of taught.
9. The Esquimau feels intuitively that bear's grease and blubber are the dishes for his table. 10. The world will not anxiously inquire who you are. 11. It will ask of you, "What can you do?" 12. The peacock struts about, saying, "What a fine tail I have!" 13. He does not know which to choose.
(See explanation of (7), above.)
14. No one can tell how or when or where he will die. 15. Philosophers are still debating whether the will has any control over the current of thought in our dreams.