The "topic sentence" is the sentence in which the main idea of the paragraph is stated. It is unquestionably the most important sentence in the paragraph. The topic sentence generally is composed of two parts: (a) the topic itself and (b) the controlling idea.
The topic is the subject of the paragraph. It is what the paragraph is all about. The following are topics suitable for a paragraph:
The SLR camera
A wedding cake
Writing effective topic sentences, however, involves more than merely stating the subject of the paragraph. A good topic sentence is specific and well focused, guiding the entire paragraph. A good topic sentence:
Has new information. It is not a fact that everyone already knows to be true (for example, A dictionary has meanings for words.).
Is specific. If the topic is too general (for example, I like camping.), the reader will not know what to expect in the paragraph.
Is general enough to invite exploration of the topic. If the topic sentence is too specific (for example, Webster's New World Dictionary has more than 40,000 words.), there will be nothing else to say on the subject.
Is strong. Starting a topic sentence with there is/are (as in There are several ways to cook rice.) is a weak opener.
Is stated in positive language. Negative language (for example, You might hate to do it, but you should keep your room clean.) should not be part of the topic sentence.
Is not an announcement. A topic sentence should draw the reader into the paragraph. Announcements (like This paragraph will discuss how to build a bird house.) hold little attraction for readers.
The Controlling Idea
Even if all of the above conditions for a topic sentence are met, an effective topic sentence needs one additional element, the "controlling idea." The controlling idea is the point of the paragraph. It guides the ideas that provide support for the paragraph and limits the scope of the paragraph. Here is an example of a topic sentence with a controlling idea that guides the support for the paragraph:
Running provides many healthful benefits.
The topic of this topic sentence is running. The controlling idea is healthful benefits. That is, the reader knows from this sentence that the paragraph is generally about running. And the reader also knows that the point of the paragraph will be to enumerate the healthful benefits of running. Limiting the scope of the paragraph through the controlling idea may happen in one of two ways.
1. The controlling idea may reveal the writer's opinion, point of view, or attitude toward the subject of the paragraph, which automatically will set parameters for discussion of the topic. OR…
2. The controlling idea itself may provide specific limitation. In either case, this limited scope, then, serves to unify the paragraph, since any discussion must be within the parameters of the controlling idea.
Here is an example of a topic sentence with a controlling idea that states the writer's opinion-the first way to limit the scope of the paragraph:
The basics of using an SLR camera can be mastered with considerable practice.
The topic of this sentence is an SLR camera. The controlling idea is mastered with considerable practice. From this single sentence the reader knows that the topic of the paragraph is the SLR camera and that the paragraph will discuss mastering the basics of using this camera. Additionally, the reader knows that such mastery comes with practice, the writer's opinion or perspective.
Here is an example of a topic sentence with a controlling idea that specifically sets limitations for the scope of the paragraph.
When writing a laboratory report, you must complete four sections.
The topic of this sentence is a laboratory report. In this sentence, the controlling idea specifically states the limitation-four sections. Thus, the reader can predict that the writer will list and describe the four sections in order.