Toni Morrison, the first African-American woman to win the Nobel Prize for Literature, has died. Some of her books — “Beloved” and “God Help the Child” — which explore the lives of African Americans in great prose and tackle issues such as slavery and misogyny, are already part of university curricula and considered classics.

Like all forms of art, literature is open to interpretation. Ask five people and you may get 10 different descriptions of what constitutes a classic novel. The English literature curriculum at schools and universities changes over the years. As time goes by, new books are added to the “must-read” category, which still includes works by William Shakespeare, Charles Dickens, and F. Scott Fitzgerald.

24/7 Tempo reached out to several English professors to compile a list of 20 English literature classics everyone should read at least once. (The list does not include novels written in languages other than English.)

“Certainly the [literary] canon has changed since I began teaching 35 years ago,” said Paula Uruburu, Ph.D., professor of English at Hofstra University. It has become more inclusive, which means more women writers, including women of color, as well as African American, Native American, Asian, continental, developing world, and LGBTQ authors, she noted. “It has also expanded to include graphic novelists.”

How and why new and old books make it into the curriculum is not rocket science. “I think the most important change has come not from any political correctness, but from humanities departments’ weakened position in the university,” said Douglas Buster, Ph.D., professor of American and English Literature at the University of Texas at Austin. Professors can sometimes teach works that please students as opposed to those that might be more challenging, he noted.

This is perhaps how some newer books are often called “classics.” Many people are reading a book, and it becomes noteworthy. For example, if you include Young Adult new classics in a list of classics, then Harry Potter might seem like a natural choice. But to answer whether it should be among the all-time literary classics like “Romeo and Juliet,” only time could tell.

People’s reading preferences change, and new authors, each with his or her own style, publish books every day. If they achieve any recognition at all, most books remain popular for a short period of time. A select few, however, stand the test of time, meritting lasting recognition. The books on the following list fall in the latter category.

Click here to see the 20 classics every American should read, according to English professors