Paragraph Writing: Topic Sentences

https://www.victoria.ac.nz/llc/llc_resources/academic-writing/

A paragraph is a group of related sentences, which develop one main idea (the topic sentence). The topic sentence tends to be a general rather than a specific idea. The main idea of the topic sentence controls the rest of the paragraph. Usually it is the first sentence in the paragraph, but not necessarily. It may come after a transition sentence; it may even come at the end of a paragraph. 

Topic sentences are not the only way to organise a paragraph, and not all paragraphs need a topic sentence. For example, paragraphs that describe, narrate, or detail the steps in an experiment do not usually need topic sentences. They are useful, however, in paragraphs that analyse and argue. They are particularly useful for writers who have difficulty developing focused, unified paragraphs (i.e. writers who tend to waffle). Topic sentences help these writers develop a main idea for their paragraphs and most importantly stay focused. Topic sentences also help guide the reader through complex arguments. 

The supporting sentences in a paragraph develop the main idea expressed in the topic sentence and provide the detail such as facts and examples. When the topic sentence comes first, the supporting sentences answer the questions the reader will develop in their minds after reading the topic sentence. In this case, the last sentence (concluding sentence) can either return the reader to the topic at the beginning of the paragraph or act as a connection to link the information with that coming up in the next paragraph. When the topic sentence comes last, the supporting sentences build up arguments and examples to make a case for the main idea contained at the end. 

Useful Tip: No writer starts with a perfect paragraph. Well formed paragraphs are the result of drafting and revising, aimed at giving the reader a coherent piece of information. There is no set length to a paragraph, but in university essays it is easier to work with paragraphs that are between four and eight sentences long.