You should write an apostrophe;

　　1. when you leave letters out. For example, when you write “I’m” instead of “I am”.

　　2. to show possession or ownership. For example, “John’s shirt is red”. “John’s” means “belonging to John” – the shirt belongs to John, so we write an apostrophe before the letter “s”.

　　You should not write an apostrophe:

　　1. in front of a letter “s” where the “s” is the plural ending of a noun. For example, “I have three books” has no apostrophe – the “s” at the end of “books” simply means that “books” is plural – there is more than one book. So, no apostrophe.

　　2. in personal adjectives and pronouns such as hers, his, its, theirs, yours.

　　There is an exercise on apostrophes which you may find helpful – if you are listening on iTunes or an iPod you will need to go to the podcast website to find the exercise.

　　I have to tell you that many English people get very confused about when to use an apostrophe and when not to. If you visit Britain, you will find lots of examples of public signs, notices in shop windows etc where someone has written an apostrophe which should not be there. The worst offenders are people who sell fruit and vegetables from market stalls You will often see signs saying “apple’s” or “orange’s” with an apostrophe that should not be there. We often call these “greengrocers’ apostrophes” – a greengrocer is someone who sells fruit and vegetables. The picture on the website shows a sign on a market stall in the town of Ely in the east of England.You will also be able to see it on the screen of your iPod. It says, “Top quality hard English conferance pear’s”. ( “Conference pears” are a particular variety of pear that grows well in England – but have you noticed that the word “conference” is spelled wrongly?) And look, there is an apostrophe before the “s” in pears. There should, of course, be no apostrophe, because “pears” here is simply the plural of “pear” – it doesn’t mean “belonging to pear”, nor are there letters left out.

　　The second bit of the notice says “3lb for 1.50”. What does “lb” mean? It means “pounds” – not pounds in money, but pounds in weight. In England, until recently, we measured the weight of things in pounds, and in America they still do. A pound is about half a kilo. When I was at school – many, many years ago – we had to learn that 16 ounces made a pound, 14 pounds made a stone, 8 stone made a hundredweight and 20 hundredweight made a ton. Yes, it was very complicated! And we had to learn about pints and gallons for measuring liquids, and inches, feet and yards for measuring distances. Nowdays, children learn metric measurements at school, and since 1995 shops must use metric measurements for everything they sell. We only use the old imperial measurements for beer and milk (where people still measure in pints – a pint is about half a litre), and for distances on roads, which are in miles – a mile is 1.6 kilometers. However, old people like me still think in the old measurements. If I cut a piece of wood, for example, I still measure it in inches and not in centimeters. When I bake a cake, I weigh the flour and sugar in ounces, not in grams. And the greengrocer in Ely market obviously finds all these modern kilos too difficult, so he or she still sells pears by the pound.