As we honour the four hundredth anniversaries of the deaths of William Shakespeare and Miguel de Cervantes Saavedra, it may be worth noting that while it’s generally accepted that the two giants died on the same date, 23 April 1616, it actually wasn’t the same day. By 1616 Spain had moved on to using the Gregorian calendar, while England still used the Julian, and was 11 days behind. (England clung to the old ­Julian dating system until 1752, and when the change finally came, there were riots and, it’s said, mobs in the streets shouting, “Give us back our 11 days!”) Both the coincidence of the dates and the difference in the calendars would, one suspects, have delighted the playful, erudite sensibilities of the two fathers of modern literature.

We don’t know if they were aware of each other, but they had a good deal in common, beginning right there in the “don’t know” zone, because they are both men of mystery; there are missing years in the record and, even more tellingly, missing documents. Neither man left behind much personal material. Very little to nothing in the way of letters, work diaries, abandoned drafts; just the colossal, completed oeuvres. “The rest is silence.” Consequently, both men have

been prey to the kind of idiot theories that seek to dispute their authorship.

A cursory internet search “reveals”, for example, that not only did Francis Bacon write Shakespeare’s works, he wrote Don Quixote as well. (My favourite crazy Shakespeare theory is that his plays were not written by him but by someone else of the same name.) And of course Cervantes faced a challenge to his authorship in his own lifetime, when a certain pseudonymous Alonso Fernández de Avellaneda, whose identity is also uncertain, published his fake sequel to Don Quixote and goaded Cervantes into writing the real Book II, whose characters are aware of the plagiarist Avellaneda and hold him in much contempt.

Cervantes and Shakespeare almost certainly never met, but the closer you look at the pages they left behind the more echoes you hear. The first, and to my mind the most valuable shared idea is the belief that a work of literature doesn’t have to be simply comic, or tragic, or romantic, or political/historical: that, if properly conceived, it can be many things at the same time.

Take a look at the opening scenes of Hamlet. Act I, Scene One is a ghost story. “Is not this something more than fantasy?” Barnardo asks Horatio, and of course the play is much more than that. Act I, Scene Two brings on the intrigue at the court of Elsinore: the angry scholar prince, his recently widowed mother wedded to his uncle (“O most wicked speed, to post/With such dexterity to incestuous sheets”). Act I, Scene Three, and here’s Ophelia, telling her dubious father, Polonius, the beginning of what will become a sad love story: “My lord, he hath importuned me with love/In honourable fashion.” Act I, Scene Four, and it’s a ghost story again, and something is rotten in the state of Denmark.

As the play proceeds, it goes on meta­morphosing, becoming by turns a suicide story, a murder story, a political conspiracy and a revenge tragedy. It has comic moments and a play within the play. It contains some of the highest poetry ever written in English and it ends in melodramatic puddles of blood.

This is what we who come after inherit from the Bard: the knowledge that a work can be everything at once. The French tradition, more severe, separates tragedy (Racine) and comedy (Molière). Shakespeare mashes them up together, and so, thanks to him, can we.

In a famous essay, Milan Kundera proposed that the novel has two progenitors, Samuel Richardson’s Clarissa and Laurence Sterne’s Tristram Shandy; yet both these voluminous, encyclopaedic fictions show the influence of Cervantes. Sterne’s Uncle Toby and Corporal Trim are openly modelled on Quixote and Sancho Panza, while Richardson’s realism owes a good deal to Cervantes’s debunking of the foolish mediaeval literary tradition whose delusions hold Don Quixote in thrall. In Cervantes’s masterpiece, as in Shakespeare’s work, pratfalls coexist with nobility, pathos and emotion with bawdiness and ribaldry, culminating in the infinitely moving moment when the real world asserts itself and the Knight of the Dolorous Countenance accepts that he has been a foolish, mad old man, “looking for this year’s birds in last year’s nests”.

They are both self-conscious writers, modern in a way that most of the modern masters would recognise, the one creating plays that are highly aware of their theatricality, of being staged; the other creating fiction that is acutely conscious of its fictive nature, even to the point of inventing an imaginary narrator, Cide Hamete Benengeli – a narrator, interestingly, with Arab antecedents.

And they are both as fond of, and adept at, low life as they are of high ideas, and their galleries of rascals, whores, cutpurses and drunks would be at home in the same taverns. This earthiness is what reveals them both to be realists in the grand manner, even when they are posing as fantasists, and so, again, we who come after can learn from them that magic is pointless except when in the service of realism – was there ever a more realist magician than Prospero? – and realism can do with the injection of a healthy dose of the fabulist. Finally, though they both use tropes that originate in folk tale, myth and fable, they refuse to moralise, and in this above all else they are more modern than many who followed them. They do not tell us what to think or feel, but they show us how to do so.

Of the two, Cervantes was the man of action, fighting in battles, being seriously wounded, losing the use of his left hand, being enslaved by the corsairs of Algiers for five years until his family raised the money for his ransom. Shakespeare had no such dramas in his personal experience; yet of the two he seems to have been the writer more interested in war and soldiering. Othello, Macbeth, Lear are all tales of men at war (within themselves, yes, but on the field of battle, too). Cervantes used his painful experiences, for example in the Captive’s Tale in Quixote and in a couple of plays, but the battle on which Don Quixote embarks is – to use modern words – absurdist and existential rather than “real”. Strangely, the Spanish warrior wrote of the comic futility of going into battle and created the great iconic figure of the warrior as fool (one thinks of Heller’s Catch-22 or Vonnegut’s Slaughterhouse-Five for more recent explorations of this theme), while the imagination of the English poet-dramatist plunged (like Tolstoy, like Mailer) headlong towards war.

In their differences, they embody very contemporary opposites, just as, in their similarities, they agree on a great deal that is still useful to their inheritors.