Definition of heading
A heading is a short phrase describing what the succeeding section is all about. You can think of it as the title of that particular section. Short documents usually do not require the use of headings. For theses and other complex readings, however, headings are important because they help readers identify the main points of each section in the paper.
Why different heading levels are needed
All right, now we know a heading is there to tell readers what a section is about. Some points are more important than others, so assigning different heading levels is necessary to indicate their significance. The level of a heading should be based on whether the idea is a main point, or a subpoint. Main points all relate to the central argument of your topic. They are like building blocks that move toward your conclusion. Therefore, they need to be clearly visible at first glance. Subpoints, on the other hand, are minor details such as statistics, or examples that support the main points. They are not significant enough to stand as main topics, but they are important enough that they should still catch the readers’ attention. 
Headings and subheadings represent the key concepts and supporting ideas in the paper. They visually convey levels of importance. Differences in text format guide readers to distinguish the main points from the rest. Headings are generally bigger, if not more conspicuous, than subheadings. Subheadings should be less noticeable than preceding subheadings.
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APA has specific formatting guidelines for each heading level that need to be followed consistently. Please see the following example.
|
Heading Level |
Format |
|
1 |
Centred, Bolded, and Title Case Heading *For Abstract and Reference List, however, Heading 1 is NOT bolded. |
|
2 |
Left aligned, Bolded, and Title Case Heading |
|
3 |
Indented 1.27 cm from the left margin, bolded, sentence case heading with a full stop. Begin body text immediately after heading. |
|
4 |
Indented 1.27 cm from the left margin, bolded, italicised, sentence case heading with a full stop. Begin body text immediately after heading. |
|
5 |
Indented 1.27 cm from the left margin, italicised, sentence case heading with a full stop. Begin body text immediately after heading. |
Aside from making your paper easier to scan, having well-structured heading levels makes it easier for you, the author, to organise your ideas while writing. While headings are considered building blocks, subheadings are to be seen as roadmaps, as they keep the author and the readers on track, and having subheadings helps you determine whether you are veering away from your main topic or not.
Things to remember when writing headings and subheadings
Keep headings concise. Headings are typically one to five words long, like a title. Subheadings, on the other hand, can be a little longer, since they expound on the heading. Think of subheadings as supporting details of the main idea (the heading) in bullet points—short and simplified. Use headings to enhance, not replace. Headings (and subheadings) should supplement the substance of your paper, not take the place of your topic sentences. They should frame your topic, not overwhelm the whole segment. Do not overdo it. Not all paragraphs need a subheading. And only use headings if you have more than one point per heading level.