Jokes aside, as I was editing a client manuscript today, the changes I was making brought to mind an online discussion I was involved in when I first started freelancing. At some point, one writer said that Word's spelling and grammar checking capabilities made the role of the copy editor obsolete. At the time I was too stunned to comment. I by no means felt that the services I offered would no longer be needed, at least, not any time soon. More than anything, it seemed naïve, like perhaps the person in question either underestimated the responsibilities of a copy editor or overestimated the capabilities of Microsoft Word's spelling and grammar check feature. Whatever the reason for the comment, most writers know that spellcheck/grammar check is not enough.
I could go into some of the more annoying issues with grammar check, like flagging complete sentences as fragments and recommending revisions that are either awkward or make no sense. But that's not my point. There are many human aspects of copy editing where word-processing programs still fall short. For this reason, even the most careful writer needs copy edit. After all, writing is a human endeavor (as is editing), and everyone is capable of error.
Whether you hire a professional or work with a grammar conscious member of a critique group, there are things that a good copy editor understands about writing that Microsoft Word does not. This is by no means a comprehensive list, just common things I see in my daily editing.
1. Writers occasionally confuse homophones. This is fairly common. I've seen the usual to, too, and two and there, their, and they're. And while Word catches these occasionally, it misses ones like isle (an island) used when aisle is needed.
2. Writers can inappropriately shift verb tenses. Your word-processing software won't catch this. If the words are spelled correctly and you've maintained subject-verb agreement, you can shift verb tenses within the same passage or even the same sentence, and grammar check will not catch it. But a copy editor certainly will.
3. A grammatically correct sentence is not necessarily a well-written sentence. Microsoft Word only looks for proper spelling and correct grammar. It does not recognize a rambling, wordy sentence or an awkwardly constructed phrase. Nor would it call frequently repeated words and phrases to your attention. These would be detected during a copy edit.
4. Writers often break the rules deliberately. A copy editor knows that sometimes the rules must be broken. This is especially true in fiction writing. Authors will often use fragments in narrative for effect or will use poor grammar in the context of dialogue, where a character may not speak in perfectly constructed sentences. This, by the way, is natural since most people don't always mind their grammar in speech.
While word-processing spellcheck and grammar check programs have improved tremendously since I started using them, they will not replace the human eyes of a copy editor any time soon. A second set of eyes can go a long way (and it shouldn't be your mom, who loves it because you wrote it, or your best friend who withholds criticism to spare your feelings). If you can't hire an editor, find a brutally honest writer friend to critique your work.