Caravaggio’s ‘David with the Head of Goliath’ was a unique self-portrait. Ostensibly, it has all the predictable features of the iconic Old Testament story. David adopts the traditional pose of personifications of justice. He is compassionate, youthful, but perhaps just slightly more melancholy than might be presumed for a young shepherd who has just miraculously defeated a philistine giant. Goliath also appears to meet expectation. He’s intimidating, brutish, and grotesque. Yet what’s unexpected is that this infamous villain, this archetypal ‘monster’ bears the unmistakable likeness of Caravaggio himself.

This was exceptional in contemporary art. Conventionally, the self-portraits of artists were ennobling – praising the artist’s own ability to create grace and virtue in a grim world. They were not supposed to act as ugly admissions of wickedness as is the case here. Clearly Caravaggio was wracked with profound guilt. Themes of culpability and sinfulness had always permeated Caravaggio’s work. In his ‘The Beheading of St John the Baptist’, Caravaggio’s signature is written in the Baptist’s spilt blood. Similarly, Caravaggio included himself in ‘The Martyrdom of St. Ursula’, peering through the dark to catch a glimpse of the murder. In addition, there is the ever-present shadow and metaphorical torment that eats away at the borders of the action in so many of his paintings.

He had always skirted the edges of public acceptability and indeed deeper morality. He was notorious for brawling in particular, even in a city where public fighting was endemic. But ‘David holding the head of Goliath’ came at a particular moral low, after the murder of a young man in a brawl. On the run, with a sizeable bounty on his head, the painting was to be a redemptive gift to Cardinal Borghese, who had found him a papal pardon.

So Caravaggio was not just the archetypal ‘monster’ artist, an angry, violent subversion of the sensitive, ruminative stereotype, but he is also the perfect example of an artist whose background and character is inextricable from their art. But can we separate the past and personal attributes of an artist from their art, even in cases where themes and ideas that dominated their real lives don’t seem to be present in the artist’s work? There might be some cases where this seems relatively straightforward. Richard Wagner was a virulent and notorious anti-Semite, but a lay person might find it quite difficult to read this anti-Semitism into his music and hence could well admire it untroubled.

This is in stark contrast, then, to the films of Leni Riefenstahl, the state-backed Nazi filmmaker who documented and glorified the 1934 Nazi Party Congress in Nuremberg in The Triumph of the Will. Yet this film, a love letter to Nazism which apotheosises Hitler, is still considered by many a technical masterpiece. It features in Steven Jay Schneider’s list of ‘1001 Movies to See before You Die’, described as “an awesome spectacle, vulgar but mythic, and technically an overwhelming, assured accomplishment”.

We should be able to separate content and form, at least in theory. This is quite easily done in the case of The Triumph of the Will, where those faceless masses and overblown military processions inadvertently stress Nazism as the ridiculous, perverse pathology it was. It’s a little more difficult in the case of Roman Polanski’s Chinatown. One of the film’s key revelations, that the villain of the piece has raped his daughter when she was 15, serves as an inescapable reminder of Polanski’s own history as a rapist and sexual abuser. Of course you might watch the film and never consider the director. His personal imprint isn’t as visible as Caravaggio’s bruised dangling face staring at his audience. But of course even describing Polanski and Caravaggio next to each other places them neatly in the single category of ‘monster’.

Most of us would agree that morality exists on a spectrum. But the uncomfortable arbitrariness of this spectrum will result in different responses. This inherent subjectivity is the key. Sometimes audiences can demonstrate a rather surprising disregard for the personalities of their favourite artists. Picasso’s misogyny didn’t turn people away from his revolutionary cubism. Paul Verlaine’s bouts of violence haven’t diminished his prominence in Decadent movement poetry. Even the murder Caravaggio committed can hardly be said to have negated the impact of his art.

Yet, audiences were repulsed by the rape and sexual abuse in Vladimir Nabokov’s Lolita and perturbed by the rape, robbery and violence of Anthony Burgess’ A Clockwork Orange. But this shock and moral outrage was directed entirely at fiction. The authors were not criminals, but were respected, and lauded as intellectual. Maybe we can forget the David Alexander on our relationship with morally reprehensible artists presence of the artist. Roland Barthes famously argued for this approach in his seminal 1967 essay ‘The Death of the Author’. He argues that to avoid limiting the possible interpretations and significance of a text, we have to forget its author and all their political opinions, as well as the wider, unconscious influence of their historical context and their personal identity.

This seems simple in theory but there are cases where the very name of an author irredeemably taints a piece of art. After all, we might well say that the art is in the space between a piece of work and the audience, but in a sense the audience’s objective appreciation is immediately skewed as soon as they hear the name of the artist. Who would not look at one of Hitler’s paintings differently on hearing his name? A corollary of this is that the more we strive to understand the fullness of art, by looking into its context and consulting its meaning as prescribed by critics and experts, the further we taint the ‘purity’ of an uninformed response. Think how dramatically different a reading of ‘David with the Head of Goliath’ might be if the audience was unaware of Caravaggio’s likeness to Goliath.

The practical difficulty we have in detaching art from artist, and following Barthes’ imperative, is seen all around us. Earlier this year, for example, students at the University of Manchester painted over the Rudyard Kipling poem ‘If’, inscribed on a wall of the newly refurbished Students’ Union. They explained that they did so because they considered Kipling prominently opposed to ‘liberation, empowerment and human rights’ and the author of ‘racist’ works. But ‘If’ is not a racist poem itself, yet it was deemed inextricable from the views of its author. We should avoid prescriptivism. Art is not a one-way process, whereby a piece can be ascribed an objective value on its release. The quality of any piece of art is something that can and should be passionately attacked by one person, doggedly defended by another and apathetically shrugged at by a third. It is, in other words, determined wholly by the individual.

The individual audience member therefore decides how much the personal qualities of an author interfere with their appreciation of their work. We might go back to ‘David holding the head of Goliath’ and remember, finally, that it acted for Caravaggio as both a literal and artistic plea for redemption. Ultimately, it didn’t save him, and he died on the way back to Rome from Naples, his saga of exile tantalisingly close to completion. Yet perhaps we can consider this a metaphor for how we approach all art produced by the personally repulsive and the morally detestable.

The work of ‘monsters’ might be virtuous, truthful, and beautiful, but it can’t absolve the artist of immorality. Should this paradox really surprise us? Why are we so shocked that people can do appalling things and yet create art that is admirable? Isn’t that the fundamental contradiction in humanity itself?