The topic sentence gives a paragraph direction and purpose. It tells what the paragraph is about (the topic), and how the writer will develop that topic (the controlling idea). Being able to identify these key ideas in a topic sentence will help you read with understanding, because you know what you’re reading about, and will improve your own expository and academic writing as you come to understand and see modeled how to write a topic sentence for yourself.

Step 1

Read the topic sentence and make sure you understand it. If you don’t know what the sentence is saying or what it means, you will have a hard time identifying its topic and controlling idea. If the topic sentence you are analyzing is not isolated or identified as part of a grammar worksheet, read the entire paragraph to which the sentence is connected.

Step 2

Identify the subject and nouns of the sentence. Most often the topic of a topic sentence is its subject. For example, “The Colorado mountains are the most beautiful in America.” "Colorado mountains" is the subject of the sentence and the topic of this topic sentence.

When a topic sentence begins with the pronoun “there” or “it,” look for the element that "there" or "it" is substituting for. For example: “There are beautiful mountains in Colorado” = “Beautiful mountains are in Colorado.” Hence, "beautiful mountains" is the topic.

Step 3

Identify the controlling idea. The controlling idea is either an opinion that needs to be proven, or an idea that leads to a list of things that need to be developed. The example, “Colorado has the most beautiful mountains” is an opinion. Someone may think that Montana or Tennessee has more beautiful mountains. Asking “how do you know?” can help you identify the controlling idea of an opinion-based topic sentence.

Identifying lists requires a “What are…” question. For example, “The life cycle of a frog has two stages.” What are the two stages? This question leads to a list. "The life cycle of the frog" is the topic, and "has two stages" is the controlling idea. Thus, the remainder of a paragraph with this topic sentence would discuss each of the two stages of a frog’s life cycle.

Step 4

Practice. Identifying the topic and the controlling idea of a sentence is not easy at first, but with practice, it will become automatic for you. There are many practice exercises and quizzes online, such as See the Resources section for more Internet exercises to help you practice.