it is possible. at least in china, a lot of people at my parents' age know how to write and read english. but they can not say a word. even you ask them to introduce themselves.that is because at that time people dont care about speaking and writing at all. but if you can speak and hear at the same time, writing and reading would be easier too. because i think learning a new language, you should pay attention to the reading ,writing, listening and speaking. well thats what my foreign teacher told me. he said learning all aspects can improve the total ability of understanding english.

I consider the written form to be just an indication, or reflection, of what is spoken and heard. It may be possible to *only* read and write English but (to draw a parallel) it's much more enjoyable to learn about food by eating it than looking at pictures. :D