The importance of topic sentences

A topic sentence states or summarizes the main idea of a paragraph.

The tendency to place topic sentences at the beginning of paragraphs can seem rather simplistic and even boring to writers from other academic traditions. This use of topic sentences as departure points for paragraphs gives a clear, predictable structure to texts, in line with the reader-orientation of Anglo-Saxon academic style.

• The topic sentence of a paragraph tends to be placed at or near the beginning. It can be placed elsewhere, but readers should be able to easily find it (often by its formulation as a declarative sentence making a claim about the topic at hand).

• Topic sentences can be complex but should clearly state the topic and focus as in this example from an introduction to a journal article:
  High and persistent levels of youth unemployment give rise to concern, as the negative consequences of extended spells of unemployment early in the career are well documented.
  [Caliendo, M., Schmidl, R. Youth unemployment and active labor market policies in Europe. IZA J Labor Policy 5, 1 (2016)]

• The convention of placing topic sentences at the beginning of paragraphs makes them very useful when skimming or scanning texts. By reading through the topic sentences one can quickly grasp the main ideas or find the location of particular information.

• The other sentences in a paragraph develop the main idea in the topic sentence, providing additional information in the form of details, evidence and examples.

Source: Some information for this post came from Academic English UK