We get inquiries about our services all the time, and one of the most frequent misunderstandings comes from the client's definition and of proofreading or editing and ours. Say Client X informs us, via email, that "the spouse" had gone over the manuscript "thoroughly," and that it only needed "a second set of eyes;" but the client's definition of "thoroughly" and ours were two different things.
First, Client X is operating under the assurance that their spouse did a "thorough" job and it's fair to assume that they did, but they do not have the training and experience of an editor who is, in essence, a professional reader. Furthermore, what the author meant by "second set of eyes?" was pretty vague. Did he mean simple proofreading for grammar and typos? Or did he want us to copy edit, or edit for content? People new to publishing may not know the differences, or even be aware that there are different levels of editing. It usually takes us a few emails to clarify what the client wants.
If you have an important document that is going to be published, it helps to understand the difference between proofreading and editing when you contract with an editing service. If you are an expert with the English language, you may indeed need a simple "second set of eyes" to give a document or manuscript a cursory check. Depending on the purpose of your document, you may actually need line editing rather than proofreading.
If you intend to send a manuscript to a publisher, you should, at the very least, have someone do line editing. This goes for any type of manuscript: fiction, non-fiction, etc. The only exception might be a book of poetry where the author's creative license allows them to play with words, spellings, punctuation, etc. Professional presentations can also benefit from proofreading as well as copy and line editing, and this includes PowerPoint presentations. There is nothing quite so embarrassing as a major typo or an incorrect fact in a presentation.
Proofreading, then, is your first step in bringing any document to an audience, and one that most writers do as they go along. Furthermore, if you have time to proofread, you can always proof your own work, but simple proofreadingshould never be considered as your final step. Hiring a professional to take your work further, especially if it is a book-length manuscript, is absolutely essential if you want to put your best foot forward.
Here are some of the differences between proofreading and editing:
Checking for spelling, punctuation, grammar, word usage, and lower level formatting issues.
Proofreading + verifying facts, checking content and organization, fixing wordiness, awkward transitions. Can suggest improvements for clarity and flow.
Proofreading + checking for grammar, punctuation, spelling, consistency, word usage, as well as assistance with rewriting/rewording.
Proofreading + fact checking, checking for inconsistencies in character behavior/speech, style issues, readability, thematic variances. Content editors can suggest improvements in style and voice without obscuring the author's voice.