An apostrophe is a signal telling the reader that a word is either a possessive or a contraction.
1) To Form Contractions
As you know, a contraction is simply two words collapsed into one. You use contractions most often in informal or personal types of writing but usually not in more formal types. When you speak, you use contractions every day. Here are some common contractions:
cannot --> cant
The apostrophe in the contractions above tells the reader that you have omitted a letter or two from the wordthe letter o in three of the cases above. Undoubtedly, you have already mastered contractions, so we wont go into detail. However, we will mention one common mistake. Remember that the apostrophe marks the missing letter. Dont make the common mistake of placing the apostrophe between the two words, such as in these cases: shouldnt, dont, etc.
2) To Form Possessives
The apostrophe is also used to mark the possessive. The possessive tells the reader that someone or something owns or possesses the thing that comes after the possessive. Here are five examples:
Ronnis word processor
The possessive noun in each of the examples above (Ronnis, bankers, banks, nations, years) indicates to the reader that something is owned by something or someone else. In most cases, to make the possessive you simply add an s to the end of the noun. This is quite easy. The problem arises when a noun is both plural and possessive. Certainly, there can be more than one Ronni, and they both can own the word processor. Or more than one banker can own the log book. In such cases, you simply place the apostrophe after rather than before the s:
Some writers become confused when they must make a possessive of singular nouns that already end in s. As usual, you make the possessive by adding s to the word; however, some writers and editors argue that the two s are redundant and that therefore you can eliminate the second s, ending up with the s. That is, they argue that there is really no need to include an s after the apostrophe, since the apostrophe already tells readers that the word is possessive. Others argue that you should drop the final s only on words of several syllables but retain it on short words. Since there is no agreement on this difficult problem, you must make your own choice. However, regardless of which option you choose, do remember to be consistent. Here are three nouns which already end in s and their corresponding possessive forms:
Finally, the apostrophe is used in one other way. Although the apostrophe is never used to make a word plural, it is used to make letters and numerals plural:
Although I received Cs and Ds in many of my college classes, I always received As in my business classes.