Musical illiteracy has as many degrees as it does consequences.
Among people who perform either instrumentally or vocally, there are some who do so entirely by ear and from memory. Others can recognize notes moving up and down the staff, but are unable to reproduce intervals correctly. Yet others may understand the meaning of time signatures and note values but cannot follow them during musical activity. The problem of illiteracy is especially acute in choruses consisting of followers and leaders, and in bands whose musically trained people have to work together with those who have no knowledge of and don't care about musical notations. The consequences of this situation have been building for the past half-century.