Firstly the word ummyia means being unable to read or write.
But we have to know also that some (UMMYS) can recognise some words (for example their names) and can even draw(write) them, and it's very easy to meet such ummys that can read certain words, some of them also are clever in some maths skills like addition or subtraction. But being ummy with such simple reading skills doesn't make you able to compose a poem for example, or write a story or novel
Read this and explain to me who is the prophet prophesized in it:
(what's written in red)
"And the vision of all is become unto you as the words of a book that is sealed, which [men] deliver to one that is learned, saying, Read this, : and he saith, I cannot; for it [is] sealed: And the book is delivered to him that is not learned, saying, Read this, : and he saith, I am not learned. Wherefore the Lord said, Forasmuch as this people draw near [me] with their mouth, and with their lips do honor me, but have removed their heart far from me, and their fear toward me is taught by the precept of men: Therefore, behold, I will proceed to do a marvelous work among this people, [even] a marvelous work and a wonder: for the wisdom of their wise [men] shall perish, and the understanding of their prudent men shall be hid. Woe unto them that seek deep to hide their counsel from the LORD, and their works are in the dark, and they say, Who seeth us? and who knoweth us? Surely your turning of things upside down shall be esteemed as the potter's clay: for shall the work say of him that made it, He made me not? or shall the thing framed say of him that framed it, He had no understanding? [Is] it not yet a very little while, and Lebanon shall be turned into a fruitful field, and the fruitful field shall be esteemed as a forest? And in that day shall the deaf hear the words of the book, and the eyes of the blind shall see out of obscurity, and out of darkness." (Isaiah 29:11-18)
more later