functional illiteracy means that a person is not able to read, write, and do math well in regular life. someone who is fully illiterate can not read, write, or do math at all. such people have perhaps never learnt how to read or write; perhaps they did not need to. a person who is functionally illiterate is different - at some point in their lives, these people were taught reading and writing skills. for different reasons, adults who are functionally illiterate try to avoid writing and reading as much as possible. that way, a person who is functionally illiterate may be able to write their name, but it is very difficult for them to write more than a few sentences.