He, She, and Nobody.

In contemporary English it is considered incorrect to use the pronoun 'they' as a singular pronoun. "If a child is unable to play piano, they should take lessons."The previous sentence is an example of a grammatically incorrect sentence. In order to use the pronoun "they" correctly, the sentence must be recast in the plural like this: "If children are unable to play the piano, they should take lessons." If you are talking about a single child whose gender is not known, it is commonly accepted that you use "he or she." This, however, is a problem when it excludes androgynes, bigendered individuals, pangendered individuals, and so on. You are either a he or a she or you don't exist as far as the English language is concerned. This is slightly outdated and could stand some adjustment.

The pronoun "they" is all encompassing, and despite some initial confusion, I think that it should be grammatically correct to use it as a singular pronoun. A consequence of this may be that we will need to be more specific and clear about whom we are talking about; a bit of practice could probably fix that. It is also important to recognize that it could only become grammatically correct through using it notwithstanding the fact that it is currently incorrect.