A subtitle is a secondary title that appears below the main title of a document or work. The purpose of a subtitle can vary depending on the context, but some common purposes for a subtitle include:
To provide more extensive information about the ideas in the text: A subtitle can be used to provide more detailed or specific information about the main ideas presented in the text.
To signal the order of importance: A subtitle can be used to indicate which ideas or points are most important, or to signal the hierarchy of ideas within the text.
To signal important details: A subtitle can be used to highlight key points or details that are particularly important or relevant to the overall message of the text.
To provide additional information about the topic of the text: A subtitle can be used to provide additional context or background information about the topic of the text, or to clarify the focus or scope of the text.