Ok, I don't know if you're referring to someone specific or you're just wondering, but anyways...I can think of a few cases where a person would never talk, but I don't know a lot about the details.
One scenario would be a deaf person. Often, they never learn to talk because they can't hear other people talking. They can often still make noises and some of them do learn to speak. So I guess their vocal chords still work. Maybe they're just underdeveloped. The terms dumb and mute can mean that a person doesn't talk at all. But I think they can refer to someone who doesn't talk due to being deaf, or someone who is physically incapable of speaking.
Then there's a condition called selective mutism. Again, I don't know a lot about it, but I think it's when a person can't speak in certain scenarios. I'm pretty sure a girl I knew when I was a kid had it. She would play and join the group, but she rarely, if ever, said a word. She couldn't even read in class. She had to read at home with a tape recorder and take it back to school. I don't know what happened, but she grew up and got over it at some point.
There's also something known as feral child. I saw a documentary on TV about it once. It's when a child is so neglected and sheltered that they don't develop normally at all. There's some critical point in their life that if they miss their chance to learn how to speak, they'll never learn. I think there was one girl that was kept in a dark closet her whole life. Then there was a boy who lived with a pack of dogs. They protected him because he helped them find food. Then he just crawled around and acted like a dog. It was really sad.
