The topic sentence tells you what the paragraph is about. Because there's only one topic developed in each paragraph, there should only ever be one topic sentence. The topic sentence of a paragraph is developed, or built on, by the addition of supporting information and details.
Here's an example of how a topic sentence can be developed.
Cheese is a very popular food in many cultures: this is our topic sentence, now let's try to develop it in a number of different ways. We can do any, or all, of the following:
Give examples: For example, cheese features heavily in both French and Italian cuisines. Indeed, even India cuisine, although not know for its use of diary products, features cheese in the form of paneer.
Use an anecdote. I have travelled widely, and eaten in many exotic locations; in all of them cheese of some kind appeared on the menu.
State reasons: The popularity of cheese could be due to its being a good way of preserving milk when there was an abundance of this commodity. Equally, it could be due to the fact that cheese is delicious!
Give facts: Half of all Italians would not consider eating a meal that did not contain cheese, and nearly 10% of the GDP of France comes from cheese taxation. (Note: these cheese 'facts' aren't true!)
In this activity, you will practice different ways of developing a topic sentence.
1. Here's your topic sentence: Out-of-town supermarkets are the subject of much controversy.
2. Try developing this topic sentence by giving examples, using anecdotes, stating reasons, giving an explanation, giving facts and figures (feel free to make these up). Remember not to stray from the main topic: a paragraph only develops one thought or idea.
Next time you need to write a paragraph, try to deliberately build up the topic sentence with supporting information.