In effect, that's what someone wanted to know when he asked online if he could use characters already in existence, such as a kidnapped princess with long hair and healing powers. He received some answers that were predictably ridiculous. Here's how I responded.
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I see you've received a couple answers so far, both of which are dead wrong and horribly misleading. Your character can have long hair, can lower herself on it like on a ladder, and even have the same name. (Most likely—more about names below.)
Ideas cannot be copyrighted, or else all of humanity would be in court defending against copyright infringement continually. Names cannot be copyrighted for the same reason. Likewise common descriptive words such as blonde, brunette, and redhead. Ditto for commonly used nouns such as tire, train, and fart (which is a bit like what the responses you've received so far smell like. And likewise for verbs such as run, procrastinate, and litigate.
People who have no idea what copyright means and what the U.S. copyright laws are shouldn't be telling other people what's copyrightable and what isn't. Phrases taken from a published work word-for-word may be copyrighted (assuming the work isn't old enough to be in the public domain, in which case you can do whatever you want with that work, including republishing and even selling it yourself). Entire sentences from a published work not in the public domain are taboo to use subject to the previous exception. In other words, the form an author uses to express himself in words—and not the names, descriptions, titles, and individual words—can be copyrighted.
Now, with that said, you can use the name Mickey and you can use the word mouse in your own writing without any fear of repercussion from copyright violation. But you can't use the name "Mickey Mouse" because, although not copyrightable, Walt the Disney Person was smart enough to take out a trademark that prevents anyone else from using that moniker. How you find out what phrases are trademarked or in the public domain is another issue entirely. You can begin with an online search of the U. S. Patent and Trademark Office. You'll find them at THIS address:
You can also contact an attorney, but that will cost a few bucks. You may want to do that in the end, anyway, if you want to be certain something isn't trademarked before you use it in your own work and risk getting blowback from the trademark holder, which is more likely than not a large, well-heeled corporate entity with a large, well-heeled legal staff on retainer.
Just my thoughts on the matter. Before taking any actions that might result in your legal embroilment, you should check with an intellectual rights attorney or, if you're a member of a writing association such as The Authors Guild, run it by their legal department. That won't cost you anything more than the cost of annual dues for membership.
Meanwhile, smoke if you've got 'em.
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D. J. Herda is author of the new series of writing advice, About Writing Right, available in eBook, paperback, and hardcover formats at Amazon and at fine booksellers everywhere. You can check out his column, "The Author-Ethicist," which runs at Substack.com weekly. Well, almost weekly. Occasionally weekly. Sometimes weekly. (Hey, I do my best!)