Producers have long been aware that one of the best ways to fill their pockets is by commissioning work adapted from other forms.

These days, the majority of new, large-scale shows borrow from other popular media. This could be film, TV, books or even recording artists’ songbooks. While the concentration is becoming greater, this principle has been in place for decades and possibly centuries.

There can be no doubt that it works commercially. Thinking about the biggest musicals around, Les Misèrables and Matilda started out as novels. The same applies to straight plays such as that perennial favourite A Christmas Carol.

With a minor variation on the theme, Harry Potter and the Cursed Child was written from scratch but uses characters who emerged and became popular in book form.

We Will Rock You and Mamma Mia are derived from pop groups’ back catalogues, while more adventurously Hamilton is based on a long, heavy biography of a previously barely remembered historical figure.

Heading the other way, this article was originally inspired by a week watching an assortment of movies including Joel Coen’s The Tragedy of Macbeth and Steven Spielberg’s West Side Story.

Theatre can also drift into TV—think of a recent remarkable example in Fleabag. Phoebe Waller Bridge somehow managed to turn an hour-long Edinburgh Fringe solo show into two seasons of highly successful television.

In many ways, allowing artistic forms to cross-fertilise must be beneficial. A youngster who enjoys West Side Story might discover that it was originally loosely based on Romeo and Juliet and be tempted to try out Shakespeare.

A more serious question is whether adaptation makes for good art. Every rule has its exceptions but this critic has grave doubts.

The adaptations of Hilary Mantel’s magisterial Wolf Hall novels on to the stage and also TV created wonderful examples of their type. However, trying to distil thousands of pages of cleverly written pastiche biography into a few hours of visual entertainment must surely diminish the experience. Similarly, when stage plays move on to film or TV, typically they are watered down and lose a great deal in the process.

The underlying reasons for the diminution should be pretty obvious. Writers generally choose their medium very carefully. If somebody wants to write a 600-page novel, they do not create a TV series.

In the opposite direction, novels written on the back of popular TV shows have a nasty tendency to show up the shallowness of the original concept. That may, in part, be because they are usually written carelessly and in a mad dash to take advantage of an audience which might slip away as soon as ratings drop.

Strangely, the best adaptations are often created from sub-standard originals. A long and tedious thriller novel can be distilled by a genius like Alfred Hitchcock into a gripping movie, where an epic tome like Midnight’s Children was always going to leave something behind when it transferred to the stage.

Watching The Tragedy of Macbeth and West Side Story also brings home the difference in intentions. While there can be no doubt that the directors involved are at the peak of their profession, their goals are very different from those of William Shakespeare and Leonard Bernstein et al.

These movies undoubtedly look gorgeous but sometimes seem intent on sacrificing characterisation and intellectual depth for overall impression. That is the nature of film, at least at the moment, while plays and literary novels operate on a completely different plane.

This is not to suggest that all adaptations lack merit or fail to entertain. After all, fans of TV series and cult movies go wild about stage versions of their favourites, laughing ahead of the gags in the same way that theatre buffs will be cowering as they anticipate the moment when Gloucester’s eyes are put out in King Lear.