Theatre has always been good at making the unreal feel like it is in reach.

Whether it be transporting an audience across time, space, or even dimension, the suspension of disbelief that theatre inspires is a rife playground for the imagination. Audiences eat up the opportunity to believe in the impossible, if only for a few hours.

That impossible belief has, for centuries, included a glimpse into the afterlife. Be it Hamlet’s ghostly father or the hallucinatory son in Next to Normal, theatremakers love to explore what may be just outside the realm of our awareness. Over the centuries, a whole host of techniques have been developed to demonstrate the concept of “spirit” onstage, ranging from mindblowingly complicated to deceptively simple.

Filmmakers, of course, have more than their fair share of obfuscating techniques in their toolbox; from technology-driven advancements like motion capture and CGI, to more practical techniques like stunt work and careful footage splicing, the screen offers artists a lot more leeway than live performance. Without the stage, however, many of film’s depictions of ghosts, ghouls, and spectral hooligans wouldn’t be possible.

Perhaps the most important technical advancement in the art of stage spirits is Pepper’s Ghost, an illusion that has been so successful that it has changed our very conception of what a ghost is supposed to look like.

Before Pepper’s Ghost, spirits were most commonly portrayed as quasi-corporeal, walking the same floorboards as the living and obeying many of the same rules of physics that govern flesh and blood. After all, how is a ghost supposed to make the haunting sounds of footsteps if their feet never touch the ground?

Pepper’s Ghost changed all of that. Named for the English scientist John Henry Pepper, who popularized the illusion in the 1800s, the technique is an early example of projection work onstage—though with no LED screens to be found! While the Ancient Greeks had to rely on body doubling and shadows to project different forms, Pepper’s Ghost harnessed light. Using a specially arranged room out of view of the audience, a plate of glass would be placed at an angle to reflect the interior of the hidden room out toward the audience.

While the glass would remain hidden for much of a performance, at key moments the stage lighting would be angled to catch the reflection of a brightly lit actor in the hidden room. The audience would then perceive the hazy projection as a ghostly figure located among the actors on the main stage. Due to the necessary angles needed to make the glass undetectable, it was functionally impossible to make the projected actor appear as though they were standing on the same floor as the actors on the main stage. Instead, a floating ghost was popularized, as was the idea of a ghost fading in and out of visibility (such levels of solid-ness could be adjusted by dimming or brightening the light shone on the hidden actor).

Pepper’s Ghost immediately became a sensation. Imagine how it must have felt to watch Macbeth swing to strike the ghost of Banquo for the first time, only for his sword to pass through him! The technique was so popular that comedy songs were soon written extolling its hypnotic powers, and there was even a shortage of plate glass due to the demand from theatres for glass screens.

While the technique is now nearly 200 years old, it is still employed across the globe. The world's largest implementation can be found at The Haunted Mansion attractions at Walt Disney Parks and Resorts. There, a 90-foot-long scene features multiple Pepper's Ghosts placed together in one setting. As park attendees travel along the path, they can see ghosts projected throughout a large, supposedly haunted ballroom. The technique has even taken off in the live music sphere, with many supposed “hologram” concerts depicting deceased artists—such as Tupac Shakur, Michael Jackson, and Elvis Presley—actually using variations of the technique rather than true hologram technology.

The principles of Pepper’s Ghost serve as the foundation from which many more digitally based techniques have since developed. The use of reflection, light, and spatial projection are practically the cornerstones for modern stage illusions.

It’s no secret that projections and LED screens are all the rage on stage these days. Their ability to transform a space with very little transition time is prized, bringing elements of the filmmaker’s toolkit into the theatremaker’s arsenal. While some shows now rely on digital projections (remember Dear Evan Hansen?), many have found a middle ground, blending the digital and the practical to great effect.

One of Broadway’s biggest proponents of this blend has been Lincoln Center Theater. The Vivian Beaumont Theater, built in 1965, has much more technological flexibility than many of the theatres built in the early 1900s, allowing for creative teams to experiment with technology without wholly committing to a screen-based set. Whether it be the perception-warping projections of Flying Over Sunset or the season shifts of Camelot, the Beaumont allows experimentation with digital effects while still prizing the impact of practical work.

Consider McNeal, currently running at the Beaumont through November 24. While the dead remain six feet under in the new play, the show does deal with a modern kind of poltergeist: Artificial Intelligence and its impact on the art-making process. McNeal incorporates a number of cutting-edge digital techniques, including deep-fake technology (which digitally alters images and videos of real people), and generative artificial intelligence (which creates images out of written requests).

[Spoiler Alert!]

At various points in the play, star Robert Downey Jr. is transformed on screens built into the set using deepfakes, appearing at various points to be Ronald Reagan, Winston Churchill, Barry Goldwater, and more. The central conflict of the show (that the title character's artistic output is based on generative AI texts he concocts from his late wife’s manuscript, Shakespeare’s The Tempest, and other key influences) is a similarly high-tech conceit. Though the show’s marketing material teased the use of holograms to act opposite Downey, in McNeal’s climax, director Bartlett Sher strips away the technology, going even further back in theatre illusion history than Pepper’s Ghost to call upon one of the simplest analog tricks: body doubling. After an hour of high concept digital effects, the switch back to practicality is shockingly effective.

Though digital effects have become more common in recent years, for many ghostly shows, practicality is becoming the hot new trend. After all, when you can’t trust anything you see on a screen, it is easy to yearn for the simplicity of something happening right in front of your eyes. In Les Misérables, the ghostly personages of Fantine and Eponine in the finale are simply played by the original actors draped in white, as are the ghosts of Our Town. Tevye’s frightening vision in Fiddler on the Roof is rendered practically, using costume, set, and lighting design techniques to briefly transport the audience into the afterlife. Even Grey House, the ghastly play that horrified Broadway in 2023, relied primarily on practical effects to present its frights.

When blurring the boundary between reality and imagination onstage, there are a number of methods available. While it is important to explore the options new technology can open, it is also key to remember that sometimes, the simplest answer is the smartest.