Editors hear this question fairly often, especially in relation to books.

Say you’ve written the book you’ve had on your mind for some time. It’s now a finished manuscript, and you can hardly contain yourself, it’s so exciting. You’ve gone over and over the book, spell-checked it and had a friend check it over for any obvious errors.

Do you need an editor? Here’s the truth: it’s very likely that you do. If you intend to publish your book, you probably need a copyeditor, at least. It’s a rare writer who leaves no typos or mistakes in a manuscript. The top pros do it, so the odds are good that you’ve got a few in there too, in spite of your friend’s help. Sometimes it takes a fresh pair of trained eyes to spot them.

A good editor not only finds and corrects grammar, punctuation and spelling errors. She spots homonyms that your spell-checker software will miss, as well as incorrect word choices or idioms that could be embarrassing. She may also comment to you where she hits a gap in logic or a seeming error in sequence or anything that snags her attention as she reads. (For example: “Which character is saying this? Hard for me to tell here.”)

And these things matter because you want your reader to understand you.

You knew what you meant when you wrote that climactic paragraph. But what you meant may not be as clear to someone else. So a good editor is an advocate for the reader: she flags things in your manuscript that could prevent the reader from easily understanding you.

It’s sad but true: readers just don’t love writers they can’t understand.

If you are sending your book to a publisher or agent, seeking a contract, you’ll want to present a professional-quality manuscript without embarrassing goofs. Once you are contracted, the publishing house will copyedit it again and proofread it after typography and book design are done, without your paying for that.

If you are self-publishing you will need the same additional editing and proofreading after the type and book design, to make sure nothing was omitted or altered in the design process. These additional editing and proofreading steps will help make sure that every detail of the finished book is correct, and as the publisher it will be up to you to demand them.

So yes, books should be edited to make sure the author’s communication arrives as it is intended to. Here’s one way to look at it: Editing is relatively inexpensive insurance that you take out on a good book to make sure your readers understand how good it is.