system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Mute people.

Can they not talk? Do they choose to not talk? Is it a disease or can their brain simply not learn language?
gpt
There are many different kinds of mutism.  

One is called selective mutism.  This is a person who *can* speak but chooses not to.  He may speak in certain situations or to certain people, or he may not speak at all.

Some people are mute because of damage to their vocal folds.  This may have been due to injury or accident, such as swallowing a corrosive substance (ie lye), cancer, or external trauma.  These people would be able to speak if not for the damage.

Other people have neurological (nerve) damage that prevents their vocal folds from moving properly to form sound.  This is generally present at birth, but could result from an event such as a stroke or traumatic brain injury.

The first three types of people can have normal intelligence and although they don't speak, can learn language and can learn to communicate in other ways.

Finally, some people are cognitively impaired to the point that they cannot learn words or language.  These people have the mental capacity of infants and usually have a very, very limited ability to communicate.

Source:  Speech Pathologist, 20 years.