A paragraph develops one idea with a series of logically connected sentences. Most paragraphs function as small essays, each with a main topic and several related sentences that support it.

How many paragraphs do you need in your paper? That depends on what you have to say. The idea that an essay should consist of five paragraphs—an introduction, three paragraphs of examples, and a conclusion—is too rigid, although some students are taught to organize information in this way. You may have more than three examples or points to make, and you may have an example or point that requires several paragraphs to develop. Don't limit yourself. Let the topic and supporting points guide you in creating logical, cohesive paragraphs.

Paragraph length

Paragraphs can vary in length. For example, short paragraphs are used in newspaper stories where the emphasis is on reporting information without discussion, or in technical writing where the emphasis is on presenting facts such as statistics and measurements without analysis. Written dialogue also consists of short paragraphs, with a new paragraph for each change of speaker. In an essay, a short paragraph can also be effectively used for dramatic effect or transition.

But the reconciliation was never to take place. Her grandmother died as Jillian was driving home from the airport.

Generally, you should avoid a series of extremely short paragraphs in your essays. They suggest poor development of an idea.

On the other hand, paragraphs that are a page or more in length are difficult for most readers, who like to see a subject divided into shorter sections. Examine long paragraphs to see whether you have gone beyond covering one idea or if you are guilty of repetition, wordiness, or rambling. But don't arbitrarily split a long paragraph. Make sure each paragraph meets the requirement of a single main idea with sentences that support it.

Paragraph unity

A unified paragraph is one that focuses on only one idea. Look at the following example of a paragraph that lacks unity.

Identification of particular genes can lead to better medicine. For example, recently scientists identified a defective gene that appears to cause hemochromatosis, or iron overload. Iron overload is fairly easily cured if it is recognized and treated early, but currently it is often misdiagnosed because it mimics more familiar conditions. The problem is that when not treated in time, iron overload leads to a variety of diseases, from diabetes to liver cancer. The identification of the faulty gene can prevent misdiagnosis by allowing physicians, through a screening test, to identify patients who carry it and treat them before the condition becomes too advanced. It is interesting that most people don't realize the exact role of iron in the body. They know that it is important for their health, but few are aware that only about 10 percent of the iron in food is normally absorbed by the small intestine. Most of the rest is tied up in hemoglobin, which carries oxygen from the lungs.

The first sentence of the paragraph presents the main idea that identification of genes leads to improved medical care. This idea is developed by the example of how the identification of a gene causing iron overload can lead to better diagnosis and early treatment. However, in the italicized sentence, the paragraph begins to wander. It is a topic sentence for a different paragraph, one about the role of iron in the body, and not about a benefit of genetic research.

Sometimes a sentence or two buried in the middle of a paragraph can break the unity of the paragraph, as in this example.

Moving out of my parents' house and into an apartment didn't bring me the uncomplicated joy that I had expected. First of all, I had to struggle to pay the rent every month, and the landlord was much less understanding than my parents. Then I realized I had to do my own laundry, clean up the place now and then, and fix my own meals. One nice thing about my mother is that she is an excellent cook. She even attended a French cooking school before she married my father. It's true that I liked the greater freedom I had in my apartment—no one constantly asking me what time I'd be home, no one nagging me about cleaning up my room or raking the front lawn—but I wasn't thrilled with spending most of a Saturday getting rid of a cockroach infestation, or doing three loads of smelly laundry on a Sunday night.

Notice how the italicized sentences interrupt the flow of the paragraph, which is really about the down side of leaving home and not about the writer's mother and her cooking skills.

To test the unity of your paragraphs, locate the topic sentence (the clear statement of the paragraph's central idea) and then test the other sentences to see if they develop that particular idea or if they wander off in another direction.

Paragraph coherence

Along with developing a single idea, a paragraph should be well organized. You can use many of the same principles—chronology, inductive and deductive patterns, and so on—that you use to organize complete essays.

Once you've decided on the order of your details, make sure the connections between sentences in the paragraph are clear. The smooth, logical flow of sentences within a paragraph is called paragraph coherence. Write each sentence with the previous one in mind.

Connecting sentences through ideas

Connect your sentences through their content, by picking up something from one sentence and carrying it into the next.

Follow a sentence that makes a general point with a specific, clear illustration of that point. Look at the following example.

The gap in pay between people with basic skills and people without them seems to be widening. In one comparison, the pay difference between women of varied mathematical skills had grown from $.93 an hour in 1978 to $1.71 an hour in 1986.

Here, the second sentence is a clear illustration of the point made in the first sentence. But look at how coherence can be lost in a paragraph, as in the following example.

The gap in pay between people with basic skills and people without them seems to be widening. Women are now playing a more important role in the work force than they have since World War II, when many had to fill the positions of men who were overseas. The pay difference between women of varied mathematical skills has grown considerably, from $.93 an hour in 1978 to $1.71 an hour in 1986.

In this example, the second sentence is not clearly connected to the first. Sentence three returns to the subject, but the continuity of the idea has been weakened.

You can also use one sentence to reflect or comment on the previous sentence, as in the following example.

The idea that in America hard work leads to financial success has been one of our most successful exports. For decades immigrants have arrived on American soil with a dream that here they can have what was impossible in their home countries, where they were limited by class structure or few opportunities.

As you review your paragraphs, be sure that such reflections logically follow from the previous statement. In the preceding paragraph, the idea about immigrants arriving on American soil with the preconceived notion that they will succeed is tied to the point in the first sentence that the American dream has been a successful export.

You can also connect sentences by asking a question and following it with an answer or making a statement and following it with a question.

Why should the government invest in research? Research leads to technological advances that create employment, as was shown in the years following World War II.
Polls indicate that many Americans favor regulation of the Internet. Are they willing to pay both with their tax dollars and their freedoms?

The sentences in these two examples are linked by words as well as by ideas. In the first example, the word research has been picked up from the question and repeated in the answer. In the second example, the pronoun they in the question has its antecedent ( Americans) in the previous statement. Be careful not to overuse the question technique, or you risk a negative reaction from readers.

Connecting with words and phrases

One way to achieve paragraph coherence is by connecting ideas. As shown in the last two examples, words and phrases can help strengthen the connection between sentences.

  • Use a pronoun whose antecedent appears in the previous sentence.

Gabriel Garcia Marquez suspends the laws of reality in his novels. He creates bizarre and even magical situations that reveal character in surprising ways.

  • Repeat a key word or phrase.

The idea of a perfect society, though never realized, continues to intrigue political philosophers. None of these philosophers seem to agree on where perfection lies.

  • Use a synonym.

According to my research, physical beauty is considered a more important asset for women than for men. Looks are everything, according to several girls I spoke to, while the boys I interviewed believed their athletic abilities and social status were at least as important as their appearance.

  • Use word patterns, such as first, second, third, and so on.

The reasons the dean announced her decision today are clear. First, students will recognize that she is listening to their concerns. Second, faculty will applaud the end of a disruptive period of indecision. Third, wealthy alumni though not particularly pleased by the plan will be happy that the controversy will be off the front page of the paper.

  • Use transitional words and phrases. Many words and phrases signal connections between sentences in a paragraph or between paragraphs in a paper. Look at the italicized words below.

The main character worships her. Later, his adoration changes to hatred.
The church stood at the top of the hill. Below stretched miles of orchards.
She treated him well. For example, she bought him a car and new clothes.
The product promised to grow new hair. But all he grew was a rash.
Hamlet disdained Ophelia. As a result, she killed herself.
Elizabeth was angry at Travis. In fact, she wanted nothing to do with him.
The plan is too expensive. Furthermore, it won't work.
No one volunteered to help. In other words, no one cared.

In the preceding examples, the italicized words or phrases clearly connect the second sentence to the first by creating a particular relationship. Vary the transitional words you use.

Following is a list of transitional words and phrases classified according to the relationships they suggest. These words and phrases, when used appropriately, can help you connect ideas in your writing.

  • Time or place: above, across from, adjacent to, afterward, before, behind, below, beyond, earlier, elsewhere, farther on, here, in the distance, near by, next to, opposite to, to the left, to the right

  • Example: for example, for instance, specifically, to be specific

  • Contrast: but, however, nevertheless, on the contrary, on the other hand

  • Similarity: similarly, in the same way, equally important

  • Consequence: accordingly, as a result, consequently, therefore

  • Emphasis: indeed, in fact, of course

  • Amplification: and, again, also, further, furthermore, in addition, moreover, too

  • Restatement: in other words, more simply stated, that is, to clarify

  • Summary and conclusion: altogether, finally, in conclusion, in short, to summarize