Substantive editing (content editing) begins when a manuscript is near completion or when it seems to be complete as a final draft, but somehow not quite finished. Substantive editing may overlap developmental editing when the editing focuses on deepening the content or rearranging or rewriting various segments. Chicago Manual of Style (CMS) considers substantive editing to be the first phase of editing, followed by copyediting or mechanical editing. CMS suggests that developmental editing is more radical than substantive editing because it involves adding new content; it restricts substantive editing to organization and presentation of existing content.
For substantive editing to be the most productive, the writer needs to be willing and prepared to make significant revisions. After reading the manuscript and marking it with comments, the editor will be able to tell you how effectively it is delivered and how an informed reader will view it in terms of style, voice, point of view, theme, organization, and language. This level of editing brings the manuscript to its greatest potential by tracking concepts, themes, and stories, and helping to fill in any missing elements. For fiction, substantive editing is the time to rescue any character that might be floundering unintentionally and to watch for consistency in dialogue.
In some instances, substantive editing begins with a detailed written assessment by the editor after reading the complete work, rather than a marked-up copy. This report, usually around ten pages long, addresses areas that are confusing or incomplete, segments requiring more documentation or research, or segments that are out of alignment with the intention of the work.