People who will sing but not speak.
There are some cases when a person who is not able to speak will still be able to sing as the result of a specific aphasia.
Aphasia is an impairment or loss of the faculty of understanding or using spoken or written language, even though there is integrity of the neuromuscular structures that produce language. Aphasia is caused by brain damage, and is produced by left brain hemisphere damage in right-handed people.
Almost 90% of the population is right handed and of this percentage, more than 99% have a strong left hemisphere dominance for the linguistic functions. This is the reason why in right handed people, only left hemisphere brain damage will cause aphasia. Left-handed people will have a different hemispheric brain pattern, so their linguistic functions will be represented in both brain hemispheres. As a result, damage in any hemisphere will produce aphasia which will be less severe than those with the same damage in right-handed people.