Deep Speech is one of D&D’s eight exotic languages. It’s the language of the Far Realm and of aberrations, a category that includes some of D&D’s most iconic monsters.
If you want to negotiate with mind flayers or beholders, Deep Speech might be the language for you.
When Will Deep Speech Be Useful?
Rarely. Most Deep Speech speakers dwelling on the Material Plane live in the Underdark, and the Far Realm is an unusual choice of adventure setting.
If your campaign never takes you into the Underdark or to the Far Realm, you might never encounter speakers of Deep Speech.
Even if you spend much of a campaign exploring the Underdark, other languages like Undercommon are much more widely spoken.
Speakers of Deep Speech are typically powerful, evil creatures. That means any Deep Speech speakers you meet are likely to be important bad guys in the campaign.
As rare as they might be, Deep Speech speakers you encounter will likely be characters worth speaking to.
Some of these creatures, like Aboleths, also exclusively speak Deep Speech, so Deep Speech may be the only way to communicate with them.
Generally though, in any campaign where Deep Speech would be useful, Undercommon will likely be more useful.
What Is the Far Realm?
The Far Realm is an anomalous plane of madness that exists outside of the rest of D&D’s cosmology. Relatively little is known about the Far Realm, but it and its inhabitants are heavily inspired by H.P. Lovecraft’s work.
Aberrations originate in the Far Realm, although most of the aberrations you encounter dwell in the Underdark. Creatures that visit the Far Realm return twisted beyond human comprehension.
Who Actually Speaks Deep Speech?
Aboleths are amphibious, tentacled creatures. They’re typically found living in ocean abysses or deep lakes, particularly Underdark lakes. They’re unimaginably old, predating even the gods of the Forgotten Realms.
Aboleths are persuasive and charismatic creatures, using their powerful telepathy to learn your innermost desires, gain your trust, and ultimately turn you to their will.
Despite their remote homes, Aboleths often have large numbers of followers. Kuo-toa, in particular, frequently worship aboleths as gods. Aboleths also often have other aberrations as followers, including chuul.
Beholders might be the most iconic of D&D’s original monsters. Creatures like dragons are ubiquitous villains in D&D, and D&D’s imagining of dragons has been massively culturally influential.
Dragons predate D&D though, where beholders are something new and unique to the game.
Beholders are striking creatures – a huge central eye floating above the ground surrounded by many smaller eyes on stalks. Beholders are fiercely distrustful with a seething hatred for any creatures unlike themselves.
Beholders frequently live beneath cities. A notable example is Xanathar who lives beneath Waterdeep.
From these places, they control and manipulate the surface creatures to create vast criminal networks and even empires.
Mind Flayers have the same arrangement of limbs as most humanoids but around their mouths are four tentacles that they use to extract and devour the brains of their victims.
Aboleths and Beholders are lone creatures that work in the shadows to gain power over the denizens of the Material Plane. Mind Flayers are different though.
Mind Flayers are hivemind creatures, controlled by giant elder brains. They form vast empires, directly conquering countless worlds and enslaving entire races of beings.
Mind Flayers are responsible for warping creatures under their control with unimaginable tortures and creating several new races of beings including the Gith and the Duergar.
There are other creatures classed as aberrations that originate from the Far Realm, and some of these also speak Deep Speech.
Most of these other Deep Speech speakers are isolated monsters without the ambitions of Aboleths, Beholders, and Mind Flayers.
These creatures are more likely to be a one-off combat encounter than the BBEG of an entire campaign.
How Did You Learn Deep Speech?
This is easily handwaved by many players. The answer to “How did you learn Deep Speech?” is often “I got a second language when I picked my race and I chose Deep Speech.”
Deep Speech is not something your character just picked up when they were a kid. It’s not a language that you learned from small-town schooling.
Someone intentionally taught you a language spoken by some of D&D’s most evil and powerful monsters.
Did you learn Deep Speech from a Mind Flayer? Then you need to explain why that Mind Flayer didn’t instead choose to suck your brain out or turn you into a mind-controlled thrall.
Wizards, Warlocks, and Clerics are often the characters with biggest excuse to know Deep Speech. These characters tend to have extensive higher education, and they may have learned Deep Speech in their studies.
A particularly studious wizard might have learned Deep Speech purely for the intellectual challenge of doing so – perhaps they searched out texts written in Deep Speech in the furthest recesses of their college’s library.
Warlocks with the Great Old One archetype likely have patrons in the Far Realm. These warlocks may have studied Deep Speech as a way of communicating with these beings so they could strike a bargain of patronage with them.
You might also view their ability to speak Deep Speech as a reward granted by their patron.
While there’s no cleric domain that directly lends itself to worshiping creatures from the Far Realm, cultists of Great Old Ones are so ubiquitous in Lovecraft-inspired fiction that this seems like an omission.
Mind-related cleric domains, like knowledge and trickery, might be easily adapted when playing a character that worships these beings.
Cultists of Far Realm creatures would have plenty of reason and opportunity to learn Deep Speech.
Player characters in campaigns that start at higher levels might have learned Deep Speech to help them in a career of hunting aberrations.
Githyanki, for example, have hunted Mind Flayers across many worlds since they escaped from their enslavement.
Deep Speech and Telepathy
Most aberrations can communicate through telepathy, so it’s often asked, “Is Deep Speech even a spoken language? Or is it entirely telepathic?”
Some players and DMs even assume that if a player character knows Deep Speech, that means they gain some telepathic ability.
None of this is the case. Deep Speech is a spoken language and, while it’s often spoken telepathically, it’s not universally telepathic.
Learning Deep Speech doesn’t grant player characters any additional telepathic ability beyond what they would otherwise possess.
What Does Deep Speech Sound Like?
5e is very vague about Deep Speech. The language doesn’t have any script associated with it, and there isn’t much information about how it sounds when spoken.
This gives you tons of freedom about how to portray the language of the realm of madness.
Some DMs like to describe Deep Speech as guttural droning noises, similar to whale song but far more sinister.
Another option is to use incomprehensible sounds that don’t comprise anything that normal creatures would or could use to communicate – sounds that are wet and organic but untethered from any sound produced by humans or animals.
My personal favorite way to describe Deep Speech is as a chattering chorus of whispers, each just barely too quiet to be understood, that conflict harshly in tone and seem to originate all around you.