Can one play an instrument without being able to sing?
Yes one can. But the instrumentalist will certainly attain the capability to sing eventually. The instrument gradually reaches his voice. If the player wishes he could sing at some point or the other. But singing is very important and helpful at an advanced level of musical accomplishment in the Indian context. Many musicians from the West nowadays come to learn Carnatic voice in order to discover their voice potentials because the western concept of voice stratifies the voices as soprano, alto, tenor and so on. Where as in the Indian musical context every voice is accepted (although good voices are delightful to hear). It is also true many instrumentalists may not remember words but can play. Knowing the words of the songs and having the ability to sing is much more demanding. Having the versatility of the technique of the instrument and being able to sing is a great accomplishment and an ideal to be followed.