"The prisoners are in prison."
Translation:Les prisonniers sont en prison.
Use "en" when it is directly followed by a noun that doesn't need an article. Ex. en prison ou en classe
Use "dans" when the following noun does need an article. Ex. dans la maison, dans la boîte, dans la voiture
You can use English as a guide: in prison, in class, versus in the house, in the box, in the car.
And you can also think about the meaning. "In prison" doesn't refer to a specific prison. "In the house" refers to a specific house.
(France is a specific country but it's actually a bad example because it's a different sort of case. Masculine countries that start with a consonant use "au", which has the article hidden in it.)
There are probably exceptions.
Thanks PeaceJoyPancakes. You are right, "en France" is not a very good example, and I will edit my response.
I just wanted to let you know that I always appreciate crossing paths with you in the sentence discussions. Thanks for your comments.
Thanks for your kind words, Tex. I appreciate your contributions too. :-)
(I think I get either the tone or the content – or both – wrong sometimes. I hope I'm improving somewhat with time though.)
Why doesn't prisonniers work as the masculine plural? Does it have to be the feminine ending when it is plural?
It can be prisonniers or prisonnières; both should be correct for this sentence. We don't know if it is a group of male prisoners, female prisoners, or a mixed group.