A paragraph is a group of sentences related to a particular topic, or central theme. Every paragraph has a key concept or main idea. The main idea is the most important piece of information the author wants you to know about the concept of that paragraph.
When authors write they have an idea in mind that they are trying to get across. This is especially true as authors compose paragraphs. An author organizes each paragraph's main idea and supporting details in support of the topic or central theme, and each paragraph supports the paragraph preceding it.
A writer will state his/her main idea explicitly somewhere in the paragraph. That main idea may be stated at the beginning of the paragraph, in the middle, or at the end. The sentence in which the main idea is stated is the topic sentence of that paragraph.
The topic sentence announces the general theme ( or portion of the theme) to be dealt with in the paragraph. Although the topic sentence may appear anywhere in the paragraph, it is usually first – and for a very good reason. This sentence provides the focus for the writer while writing and for the reader while reading. When you find the topic sentence, be sure to underline it so that it will stand out not only now, but also later when you review.
Identifying the Topic:
The first thing you must be able to do to get at the main idea of a paragraph is to identify the topic – the subject of the paragraph. Think of the paragraph as a wheel with the topic being the hub – the central core around which the whole wheel (or paragraph) spins. Your strategy for topic identification is simply to ask yourself the question, "What is this about?" Keep asking yourself that question as you read a paragraph, until the answer to your question becomes clear. Sometimes you can spot the topic by looking for a word or two that repeat. Usually you can state the topic in a few words.