When are words art?

 As the weather has been inclement I have had several opportunities to visit local galleries.
In one a full wall was taken up with pages ripped out of  books and with sentences highlighted.
On the other side of the gallery the artist had rubbed the words off pages and the dust made by the rubber was then heaped in piles on a pedestal.
I have long found it fascinating that when you visit some modern art exhibitions the explanation of the work requires a degree to understand. Surely it is better for a work to stand on its own!
This was contradicted on a recent visit where the artist had used sentences to form a picture. 
These were both in Arabic and English and overlaid. This proved to be an effective use of words within a piece of art.

​In another gallery I saw the opposite of this where traditional paintings were hung. Viewers could look at these and imagine what is happening or being said.
Surely this engages the viewer and no written explanation is needed.