When you mean “for example,” use e.g. It is an abbreviation for the Latin phrase exempli gratia. When you mean “that is,” use “i.e.” It is an abbreviation for the Latin phrase id est. Either can be used to clarify a preceding statement, the first by example, the second by restating the idea more clearly or expanding upon it. Because these uses are so similar, the two abbreviations are easily confused. If you just stick with good old English “for example” and “that is” you won’t give anyone a chance to sneer at you. If you insist on using the abbreviation, perhaps “example given” will remind you to use “e.g.,” while “in effect” suggests “i.e.”
Since e.g. indicates a partial list, it is redundant to add “etc.” at the end of a list introduced by this abbreviation.
It looks cheesy to spell “hundreds” as “100’s”; and it isn’t really logical because “100” doesn’t mean “hundred”—it means specifically “one hundred.”
“A.D.” does not mean “after death,” as many people suppose. “B.C.” stands for the English phrase “before Christ,” but “A.D.” stands confusingly for a Latin phrase: anno domini (“in the year of the Lord”—the year Jesus was born). If the calendar actually changed with Jesus’ death, then what would we do with the years during which he lived? Since Jesus was probably actually born around 6 B.C. or so, the connection of the calendar with him can be misleading.
Many Biblical scholars, historians, and archeologists prefer the less sectarian designations “before the Common Era” (B.C.E.) and “the Common Era” (C.E.).
Traditionally “A.D.” was placed before the year number and “B.C.” after, but many people now prefer to put both abbreviations after the numbers.
All of these abbreviations can also be spelled without their periods.
“AM” stands for the Latin phrase Ante Meridiem —which means “before noon”—and “PM” stands for Post Meridiem : “after noon.” Although digital clocks routinely label noon “12:00 PM” you should avoid this expression not only because it is incorrect, but because many people will imagine you are talking about midnight instead. The same goes for “12:00 AM.” You can say or write “twelve noon,” “noon sharp,” or “exactly at noon” when you want to designate a precise time.
It is now rare to see periods placed after these abbreviations: “A.M.”; but in the US, in formal writing it is still preferable to capitalize them, though the lower-case “am” and “pm” are now so popular they are not likely to get you into trouble. The lower-case forms are standard usage in the UK.
Occasionally computer programs encourage you to write “AM” and “PM” without a space before them, but others will misread your data if you omit the space. The nonstandard habit of omitting the space is spreading rapidly, and should be avoided in formal writing.
“Etc.” is an abbreviation for the Latin phrase et cetera, meaning “and the rest.” (Et means “and” in French too.) Just say “et cetera” out loud to yourself to remind yourself of the correct order of the “T” and “C.” Also to be avoided is the common mispronunciation “excetera.” “And etc.” is a redundancy.
source :http://public.wsu.edu
