An interesting site that I found online is Guide to Grammar and Writing. The basic rules for italics and underlining are included on the site at Using Italics and Underlining.
However, some works you'll find in print are only capitalized. According to the Guide (and other sources), "We do not italicize the titles of long sacred works: the Bible, the Koran. Nor do we italicize the titles of books of the Bible: Genesis, Revelation, 1 Corinthians." This would also include the Vedas.
Furthermore, legal or public documents are capitalized but not italicized: the Constitution, the Declaration of Independence, and the Magna Carta.
We italicize letters and words when referring to them as words: dot the i's in citizens; note, though, that the apostrophe and s are not italicized. Other examples: "You have three the's in that sentence."
Some fun with plurals:
- The plural of passer-by is passers-by.
- The plural of mother-in-law is mothers-in-law.
Other eccentricities for plurals:
- In the USA, we say "in the 1800's . . ." although in Britain (and some in America) are beginning to use the form "in the 1800s."
- Particular decades can be contracted, but we would write '60s, not '60's--too many apostrophes, according to some. One could write "The 1800s were different than the '60s" or "The 1800's were different than the 1960's."
Language is dynamic and changes over time. The important point is to be consistent with the application of rules within a particular document.
Although there are many sources for the rules and strategies of correct writing, two excellent sources are the following:
Copyright 2010 by Thomas L. Kepler, all rights reserved