** LEGAL UPDATE **
All applicants for naturalized U.S. citizenship, and in particular readers of Nolo's Becoming a U.S. Citizen, will need to make sure they're using the latest version of Form N-400. A new one came out from U.S. Citizenship and Immigration Services (USCIS) in September, 2019. Failure to use it will, beginning December 16, 2019, result in USCIS sending it back to you or delaying its processing until you have paid the fee.
How different is the new form? Hardly at all! You'll find all the same questions as before, in the same order. That means the instructions in the Nolo book mentioned above are still good.
However, take note that the sample N-400 in the ninth edition of Nolo's book contains a printing error. The book correctly explains that only certain types of people can safely answer "No" to any of Questions 45-50 in Part 12 of the form, which ask:
Most people should simply answer "Yes" to all of these.
Unfortunately, the ninth edition of Becoming a U.S. Citizen shows "X" marks in the "No" column. Please disregard this portion of the sample, and enter the answers that are true in your case; again, that's ideally "yes" to each one.
See an attorney is your answer is actually "No" and if you do not fit any of the categories described next.
If this application is being filled out for a person who is disabled to the point of being unable to understand the Oath Waiver, Question 46 provides a place to indicate that, and it's possible to answer "No" to it.
Or if you are a conscientious objector (CO), meaning that for religious or moral reasons you refuse to take up weapons or join in a war, you can answer "no" to Question 48 and possibly 49, if you also provide proof of your CO status.
Members of a religion that prohibits taking any sort of oath (for example, the Quakers and the Jehovah's Witnesses can answer "no" to Question 47, but must provide a letter from their church or other religious body confirming membership.
To repeat: In most other cases, applicants for naturalized U.S. citizenship must check "Yes" to Questions 45-50 of Form N-400.
Effective Date: December 16, 2019