A paragraph should be unified around a main point. The point should be clear to readers, and all sentences in the paragraph should relate to it.
Stating the main point in a topic sentence
As readers move into a paragraph, they need to know where they are—in relation to the whole essay—and what to expect in the sentences to come. A good topic sentence, a one-sentence summary of the paragraph’s main point, acts as a signpost pointing in two directions: backward toward the thesis of the essay and forward toward the body of the paragraph.
Like a thesis statement (see 1c), a topic sentence is more general than the material supporting it. Usually the topic sentence (highlighted in the following example) comes first in the paragraph.
All living creatures manage some form of communication. The dance patterns of bees in their hive help to point the way to distant flower fields or announce successful foraging. Male stickleback fish regularly swim upside-down to indicate outrage in a courtship contest. Male deer and lemurs mark territorial ownership by rubbing their own body secretions on boundary stones or trees. Everyone has seen a frightened dog put his tail between his legs and run in panic. We, too, use gestures, expressions, postures, and movement to give our words point.
—Olivia Vlahos, Human Beginnings
Sometimes the topic sentence is introduced by a transitional sentence linking it to earlier material. In the following paragraph, the topic sentence has been delayed to allow for a transition.
But flowers are not the only source of spectacle in the wilderness. An opportunity for late color is provided by the berries of wildflowers, shrubs, and trees. Baneberry presents its tiny white flowers in spring but in late summer bursts forth with clusters of red berries. Bunchberry, a ground-cover plant, puts out red berries in the fall, and the red berries of wintergreen last from autumn well into the winter. In California, the bright red, fist-sized clusters of Christmas berries can be seen growing beside highways for up to six months of the year.
—James Crockett et al., Wildflower Gardening
To hook readers, writers are sometimes tempted to begin paragraphs with vivid quotations or compelling statistics from a source. A topic sentence in the writer’s own words, however, can remind readers of the claim of the paper, advance the argument, and introduce the evidence from a source. In the following paragraph on the effects of the 2010 oil spill in the Gulf of Mexico, the writer uses a topic sentence (highlighted) to state that the extent of the threat is unknown before quoting three sources that illustrate her point.
To date, the full ramifications [of the oil spill] remain a question mark. An August report from the National Oceanic and Atmospheric Administration estimated that 75 percent of the oil had “either evaporated or been burned, skimmed, recovered from the wellhead, or dispersed.” However, Woods Hole Oceanographic Institution researchers reported that a 1.2-mile-wide, 650-foot-high plume caused by the spill “had and will persist for some time.” And University of Georgia scientists concluded that almost 80 percent of the released oil hadn’t been recovered and “remains a threat to the ecosystem.”
—Michele Berger, “Volunteer Army”
Occasionally the topic sentence may be withheld until the end of the paragraph—but only if the earlier sentences hang together so well that readers perceive their direction, if not their exact point.
Sticking to the point
Sentences that do not support the topic sentence destroy the unity of a paragraph. If the paragraph is otherwise focused, such sentences can simply be deleted or perhaps moved elsewhere. In the following paragraph describing the inadequate facilities in a high school, the information about the chemistry instructor (highlighted) is clearly off the point.
As the result of tax cuts, the educational facilities of Lincoln High School have reached an all-time low. Some of the books date back to 1990 and have long since shed their covers. The few computers in working order must share one printer. The lack of lab equipment makes it necessary for four or five students to work at one table, with most watching rather than performing experiments. Also, the chemistry instructor left to have a baby at the beginning of the semester, and most of the students don’t like the substitute. As for the furniture, many of the upright chairs have become recliners, and the desk legs are so unbalanced that they play seesaw on the floor.
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