At first glance, The French Lieutenant’s Woman appears to be a modish, postmodern product of the 1960s, a dry intellectual exercise carefully designed to draw the reader’s attention to its own artificiality. In the very first paragraph, John Fowles tells us his book is set in 1867, 100 years before he wrote it. From then on, he drops in invitations to step outside the text and think about the person writing it, alongside the variously fraught characters he’s pushing around Victorian Lyme Regis.

He even interrupts himself in chapter 13, just to say:

I do not know. This story I am telling is all imagination. These characters I create never existed outside my own mind. If I have pretended until now to know my characters’ minds and innermost thoughts, it is because I am writing in (just as I have assumed some of the vocabulary and ‘voice’ of) a convention universally accepted at the time of my story: that the novelist stands next to God. He may not know all, yet he tries to pretend that he does.

Fowles may be denying omniscience, but he makes no attempt to pretend he isn’t a smarty-pants, adding: “But I live in the age of Alain Robbe-Grillet and Roland Barthes: if this is a novel, it cannot be a novel in the modern sense of the word.”

That begs the question of what the novel “in the modern sense of the word” may be? The implication, confusingly enough, is that a modern novel is a postmodern one, since Fowles names both a leading postmodernist (Barthes) and a thinker credited with pointing the way towards it (Robbe-Grillet). The latter’s big contention, when he wrote Towards a New Novel in 1963, was that the novel is a form that must constantly evolve. Meanwhile, Barthes argued that the author is dead; authorial intentions should be disregarded.

Already you can see why Fowles might separate himself from those kinds of ideas in his self-conscious re-creation of the Victorian form. But The French Lieutenant’s Woman is still characterised as a postmodern exercise. What could be more postmodern than interrupting your narrative to disavow postmodernism?

However, Fowles’s thoughts on his own writing make his process seem less self-conscious than subconscious. He is most concerned with his characters’ independence; they will not do as he “orders”, instead acting “gratuitously” and with “autonomy”. He denies that his interruptions break the “illusion” of their reality because “my characters still exist”.

Fowles expanded on this idea in an essay published in Harper’s Magazine in 1968, called Notes on an Unfinished Novel. There, he wrote that The French Lieutenant’s Woman started not with an intellectual idea, but an image: “A woman stands at the end of a deserted quay and stares out to sea. That was all.”

The quay became “specific” to him, as he could see the famous Lyme Regis Cobb from the bottom of his garden. The woman “seemed” Victorian, but since she was standing “with her back turned”, she struck him as a “reproach” to the age. And so the novel began to build. “Follow the accident, fear the fixed plan – that is the rule,” says Fowles. “Writing is like eating or making love: a natural process, not an artificial one.”

Fowles relied on his imagination; he even claimed to have been writing “science fiction” at certain points because no “respectable” (the scare quotes are his) Victorian novelist had ever described a couple in bed, leaving him with no guide when he came to write such a scene himself.

One place where Fowles did have good precedents was in authorial interventions. He quotes Thackeray at length, who clambered over the fourth wall to chat away to his readers and make them question who the narrative “I” was. (Thackeray carried out all kinds of tricks it would be tempting to call postmodern, if we didn’t know better.) So it is with Fowles, who claimed that his “I” doesn’t break the illusion of his story – rather, he is an emotionally involved part of it. Late on in the Harper’s essay, as the book nears publication, he says he hates the day the book goes to press because it is the day “the people one has loved die”.

So much for the thesis. It hasn’t been a “crossword puzzle” at all, he tells us. Writing the novel has been a mysterious process. He has been guided by emotion and instinct as much as intellect. And perhaps that’s why this book remains so engaging to read 50 years after its publication and 150 years after its setting. It comes from the heart as much as the head.