The topic sentence of a paragraph sums up the author's point or message. Take, for instance, the following paragraph. Which sentence do you think does the best job answering the question, What's the author's point?
The 1920s began on a note of economic optimism. However, by the end of the decade, America was sinking into an economic depression that left the country reeling. Automobile sales, the heart of the early twenties consumer boom, were bottoming out. Housing starts fell, along with manufacturing output. In the fall of 1929, the stock market crashed with investors losing as much money as the government had spent during all of World War I. Those without investments on Wall Street were facing even grimmer prospects. Jobs were disappearing as factories and businesses closed their doors. For many working people, it wasn't clear if they would have a roof over their head or enough food to feed themselves and their families.
Sentence 2 is the only sentence in the paragraph that answers the question, What's the point of the paragraph? Sentence 1 is about the optimism of the early twenties. But as you can see, the paragraph does not go on to describe happy or positive moments. All sentence 1 does is pave the way for the turnabout in the next sentence.
If you tried to use any of the remaining sentencessentences 3 through 8to sum up the paragraph's message, you would find them too specific. The paragraph is not limited to decreasing car sales, failing investments, or job losses. These are all specific examples of the more general "economic depression that left the country reeling" mentioned in sentence 2. In other words, the other sentences are not broad or inclusive enough to summarize the entire paragraph, and we have to consider sentence 2 as the topic sentence.
Topic sentences, particularly in textbooks, are most likely to be the first, second, or third sentence in a paragraph. Topic sentences, however, can appear anywhere. Thus you can't always rely (even in textbooks) on the second (or third) sentence to pick up the train of thought begun by the first (or second) sentence. Still, no matter where the topic sentence appears, the criteria, or standards, you use to identify it remain the same.
They are as follows:
With those four criteria in mind, take a look at the next paragraph. Where's the topic sentence?
Whenever a dictionary gets revised, the editors have to select those words worthy of making its pages. Sometimes that decision is difficult because it's just not clear which words have entered the English language long-term and which ones reflect momentary fads that will be gone in a year or two, along with the words that described them. The following words, though, don't fall into that "iffy" category; they seem to be keepers, deserving of an entry in any comprehensive, or complete, dictionary. The word "telenovelas," for instance, refers to the Spanish version of soap operas. Given the popularity of this particular entertainment form, room for it will have to made in the T section of every desk dictionary. The same is true for "Bollywood," the name given to movies made in Bombay, India and modeled on old Hollywood films that were heavy on passionate romance, singable tunes, and superficial plot lines (note that Bombay now calls itself "Mumbay"). It's also hard to believe that references to I-pods are going to disappear anytime soon; so "IPO," initial public offering and "Ipoh," a city in Malaysia, should get ready to make space for a new entry. It's also probably true, too, that the word "gninormous," meaning "huge" or "gigantic," is not just a flash in the pan. Thus it's very likely to turn up in updated dictionaries, probably accompanied by "technostalgia" (a longing for simpler forms of technology that have been replaced); "McMansions" (large, expensive houses that appear to have been mass-produced), and "Internots" (people who refuse to use the Internet to communicate).
If you are debating whether or not you've identified the topic sentence correctly, turn the sentence you've chosen into a question. If the remaining sentences seem to answer that question, you have discovered the topic sentence, for instance, "What words are keepers that should definitely find their way into a dictionary?" Since the remaining sentences answer precisely this question, sentence 3 is definitely the topic sentence.