Salman Rushdie has the most illuminating answer I've come across in his essay, A Fine Pickle. Here's an extract:

What is essential? It’s one of the great questions of life, and, as I’ve suggested, it’s a question that crops up in other adaptations than artistic ones. The text is human society and the human self, in isolation or in groups, the essence to be preserved is a human essence, and the result is the pluralist, hybridised, mixed-up world in which we all now live. Adaptation as metaphor, to paraphrase Susan Sontag, adaptation as carrying across, which is the literal meaning of the word “metaphor”, from the Greek, and of the related word “translation”, another form of carrying across, this time derived from Latin.

Many adaptations are too faithful to recreating the original in a different form. The BBCs Women In Love is guilty of this. Beautifully shot and well acted, it's devotion to the DH Lawrence's novel stultifies and cramps it's life as an individual work of art. Would we think it a great work had we only watched the TV adaptation?

Not for a second.

Which reminds us, an adaptation must adapt. It has to be inspired to replicate the beauty, the essence of the original. But be brave enough to reinvent its old self in the auspices of the new.

Wes Brown is a novelist and NAWE Young Writers' Coordinator.