Zeev:
I'll answer for Penni, who will probably agree.
Its (no apostrophe) is possessive, the neuter form of his or hers. (In English the gender of the possessive pronoun goes with the person (man, woman or thing)who is doing the possessing, as in German, not as in the Romance languages, where the possessive pronoun modifies the thing possessed.)
Examples: The boy sees his mother. The girl sees her mother. The book rests in its place on the shelf.
There is no apostrophe for the possessive.
The apostrophe is used to indicate a contraction, leaving something out. Examples:
It's a beautiful day! (It's is a contraction for it is).
Unfortunately, it gets confusing when we leave the realm of the possessive pronoun, because with ordinary nouns, the apostrophe serves both to denote possession and contraction with the linking verb is. Examples:
John's hat fell off. (Possessive, belonging to John) John's the best student in the class. (Contraction for John is).
But to answer your question simply:
It's = it is Its = belonging to it.
"Right" is used in several ways: 1. the opposite of "left" 2. correct, the opposite of "wrong" 3. the political right, as opposed to the "left" 4. as an adverb roughly equivalent to "rather". Ex: "He had a right hard time getting into college." This use is somewhat colloquial and regional (Southern). In the South you will sometimes hear the expression "right smart", meaning a goodly number or amount. This is nearly archaic; frequently seen in Shakespeare and Chaucer. 5. There may be other uses of "right" but none springs immediately to mind. Let me know if there is any specific use you question.
Troth: I don't know of any modern use for this word. It is mainly heard in old expressions such as "pledge one's troth" meaning to promise marriage.
Jack |