A codicil is a document that's added to an existing, signed will, to change it or add new provisions to it. The word codicil has been around since the 1400s, but now that most wills are created electronically, it's often easier—and clearer—just to make a new will.
Wills, unlike most other legal documents, aren't valid unless they are signed in front of two adult witnesses. The witnesses aren't there just to make sure you're who you say you are. They sign their own statement at the end of your will, declaring that you seemed of sound mind and not under undue influence—in other words, that it looked to them like you understood what you were signing and were acting of your own free will.
This witness requirement for wills isn't likely to go away anytime soon. Wills are simply different from other documents because if there's a dispute over one, the key person—the one who signed it—won't be around to explain what he or she meant. By contrast, if people are arguing about, say, a contract, both of them can go into court and do their best to convince a judge or jury of their point of view.
A few states are chipping away at the witness requirement, by allowing people to sign in front of a notary public instead of witnesses, but it's definitely the exception to the rule. After all, a notary public checks your driver's license and verifies your identity, but isn't asked to form any opinion about your mental state.
How does this affect codicils? Because they are just like wills, witnesses are required for them, too. So if, after you make and sign your will, you want to add a new paragraph with a codicil, you'll have to sign the codicil in front of two witnesses, just like the original will.
You can make your will online, quickly and easily, using Nolo's Online Will.
Most of us will eventually want to change the first will we make. After all, circumstances change: we marry, divorce, have children, have spats with our relatives, take up and abandon charitable causes. One "last will" isn't likely to carry us through to the end.
The witness requirement for the codicil, plus the ease of using computers to prepare, modify, and print documents, erases any reason to make a codicil. When legal documents were painstakingly written out with quill pens, it made sense not to rewrite a whole will if you could just tack on a brief codicil. But these days, there's no advantage to a codicil.
There is, however, a drawback: A codicil is unlikely to seamlessly fit with the original will. Is it a pure addition, or does it negate something in the original document? If it's supposed to replace part of the first will, which part?
The solution is simple: Just make another will. These days, it's easy to start from scratch, using software or an online service. Or start with your original will, which is surely on a computer somewhere—in your home or office, if you prepared it yourself, in an online service's files, or in your lawyer's office if you hired someone to prepare it. (Lawyers don't use quills anymore, either.) If you can't get your hands on the file, just retype it—carefully. And then get those two witnesses to watch you sign.