DEEP in the vast La Sante prison in Paris, law student Morgane is discussing the classic novel "The Outsider" by Albert Camus with one of the prisoners.

Adama finds some of the language tricky, but said reading is a "lifeboat".

"It allows me to escape, to think of something else. I imagine the scenes in my head. It's as if I was directing a TV show," he told AFP.

Morgane is a volunteer with the charity "Lire Pour Sortir" (roughly: "Read to Get Out"), which sees reading as more than a metaphorical form of escape.

It is championing reading as a way to tackle France's overflowing prisons, currently 20 percent over capacity.

Lack of vocabulary is "the number one determining factor in social inequality," said lawyer Alexandre Duval-Stalla, who set up the charity in 2015.

"The more words you have, the better chance of a job, of inserting yourself into life," he told AFP.

A good vocabulary not only helps when speaking to judges, but can also prevent crimes in the first place, he said.

"All this aggression and impulsiveness we find with criminals comes from being unable to express themselves."

- Illiteracy -

Adama's choice of Camus is apt. The Franco-Algerian writer's own mother was illiterate, with a vocabulary of only around 400 words. It was a barrier between them, despite his lifelong devotion.

"The Outsider" also tells the story of a young man who ends up in prison facing the death sentence.

Almost a quarter of France's 72,173 prisoners are illiterate, according to government figures.

French prisons are required to have libraries, but not librarians -- who encourage reading, help detainees and organise cultural programmes.

Pressure is mounting. A new law, in force since January, scrapped automatic sentence reductions for good behaviour -- detainees must now show they have engaged with a cultural or work programme.

But lack of resources means many are unable to access the necessary programmes.

Lire Pour Sortir wants to help fill the gap and will double its volunteer network to 500 by 2024. But even then, it will still be in only 50 of France's 187 prisons.

- Perspective -

Books help perform the work that would ideally be done by psychologists if the resources existed, said Duval-Stalla.

"Criminals rarely put themselves in another person's shoes. Books allow them to live the stories of other people, and that's very important. Words give you perspective and the tools for reflection," he said.

La Sante, which was recently renovated, could provide an example.

Lire Pour Sortir runs its library and hired a professional librarian. Neat and tidy, with posters on the wall and an atmosphere of calm -- it could be the library of a small village, if not for the bars on the windows and guards at the door.

But with only 20 inmates permitted at a time, the waiting list is long. "We are victims of our own success," said its librarian Jean-Baptiste Devouassoux.

"We know what keeps people out of prison -- a job, housing, a family," said Duval-Stalla. "But also the capacity to express and understand yourself -- and that requires words."