Briefly, you must use a possessive apostrophe when something belongs to something else: ‘Europe’s cities’, for instance. For plural nouns ending in an s, only add a single apostrophe: ‘European cities’ development’.
At the same time, don’t be tempted to add apostrophes just for the sake of it, as in the famous greengrocers’ apostrophe: ‘cabbage’s 50p a kilo’, etc: here, ‘cabbages’ is a simple plural – let it be one.
Use apostrophes also for contractions: ‘There’s a star in the night sky’; ‘You’re a big girl now’; ‘Don’t give up’; ‘Wouldn’t it be nice’, etc.
Common spelling and grammatical errors
- It’s/Its. ‘It’s’ is only ever used when it’s a contraction for it is; given that you should generally avoid using contractions, you are unlikely to be writing “it’s”. More often than not, you will be writing “its”. ‘Its’ is a perfectly normal and inoffensive word in itself and should be used on every other occasion. Practise by writing it out and forcing yourself not to think that it looks wrong.
- Principle/principal. ‘Principle’ refers to a guide or maxim or rule by which something is judged; ‘principal’ means leading or foremost, or the leading or foremost person. As in ‘The principal is a man with certain principles’.
- (In)dependent/(in)dependant. Independent (as in the newspaper) is the spelling for the concept of someone or something not being biased or reliant on anyone or anything else; the reverse is dependent. Use ‘dependant’ only where you are referring to a person or persons, as in ‘These children are dependants of their stepfather’.
- Effect/Affect. ‘Effect’ describes the consequence of something, and can be used as a verb, ‘to effect’, meaning to deliberately cause something to happen (‘Spock’s noble self-sacrifice effected the salvation of the USS Enterprise’). ‘Affect’ is a verb meaning to influence something, usually in an inadvertent way, and usually involving feelings: (‘The death of Spock in The Wrath of Khan affected me to tears’).
- Lead/led. The past participle of the verb ‘to lead’ is ‘led’, not ‘lead’, as in, ‘Last Saturday, I led my dog to the canal and drowned him’.
- Argument. This is the correct spelling, not ‘arguement’.
- Fewer/Less. ‘Fewer’ refers to numbers of people or things; ‘less’ refers to an amount. ‘I drank less beer yesterday than usual’ is correct, ‘I ate less fishfingers than usual’ is wrong. The same principles go for the abuse of the word ‘amount’: it is wrong to talk about, say, ‘the amount of people who are Chelsea fans’, as if you meant that they could be weighed; the correct word is ‘number’.
- Definite. This is the correct spelling, not ‘definate’.
- Separate. This is the correct spelling, not ‘seperate’.
- ‘Comma splicing’. This is the term used for joining two sentences with just a comma, it is very common indeed. That last sentence was deliberately written wrongly: find another way of writing this, as in ‘This is the term used for joining two sentences with just a comma, and it is very common indeed’. Alternatively, use a semi-colon, as in: ‘This is the term used for joining two sentences with a comma; it is very common indeed’.
- Practice/Practise. The first is a noun, the second a verb (in English usage, though not in American English, where practice is both noun and verb. ‘I practise taxidermy on my pets. I am getting better with practice’.
- Adjectival hyphens. When compound words form adjectives, as for instance ‘nineteenth’ and ‘century’ before ‘painting’, use a hyphen to indicate that these form a single adjective (something which describes something else). You could say ‘In the nineteenth century, realism was the principal artistic style’, but you should also say ‘Realism was crucial to nineteenth-century art’.
There are many more mistakes out there, but these are very common and can be dealt with very easily if you only take care. After a while, you won’t need to think about it. Don’t rely on spelling and grammar checkers – these are good and helpful, and will improve your writing, but they will miss many things, and you really need to understand the underlying principles; furthermore, when you go back to handwriting exams, it is all too easily to fall back on bad habits.