+If+ may connect a clause expressing +condition+, +time+, or +concession+, or it may introduce a +noun+ clause.
6. If a slave's lungs breathe our air, that moment he is free. 7. If wishes were horses, all beggars might ride.
8. Who knows if one of the Pleiads is really missing? [Footnote: Many grammarians say that if here is improperly used for whether. But this use of if is common with good authors in early and in modern English.]
9. If the flights of Dryden are higher, Pope continues longer on the wing.
+Lest+ may connect a clause expressing +purpose+, or it may introduce a +noun+ clause.
10. England fears lest Russia may endanger British rule in India. 11. Watch and pray lest ye enter into temptation.
+Since+ may connect a clause expressing +time+, +cause+, or +evidence+.
12. It must be raining, since men are carrying umbrellas. 13. Many thousand years have gone by since the Pyramids were built. 14. Since the Puritans could not be convinced, they were persecuted.
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