+Explanation+.—For introduces the subject phrase; the principal part of the entire phrase is us to know our faults; the principal word is us, which is modified by the phrase to know our faults.
5. God never made his work for man to mend.
+Explanation+.—-The principal term of the phrase for man to mend is not man, but man to mend.
6. For a man to be proud of his learning is the greatest ignorance.
The +infinitive phrase+ may be used as an +explanatory modifier.+
7. It is easy to find fault.
\to
\ find | fault
\——-'———
|
It (/ \) | is \ easy
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+Explanation+.—The infinitive phrase to find fault explains the subject it. Read the sentence without it, and you will see the real nature of the phrase. This use of it as a substitute for the real subject is a very common idiom of our language. It allows the real subject to follow the verb, and thus gives the sentence balance of parts.
8. It is not the way to argue down a vice to tell lies about it. 9. It is natural to man to indulge in the illusions of hope. 10. It is not all of life to live. 11. This task, to teach the young, may become delightful.
The +infinitive phrase+ may be used as +objective complement.+