Does the Detect Thoughts spell work against an Intellect Devourer?

Question

The spell Detect Thoughts has the following limitation on potential targets:

You can't detect a creature with an Intelligence of 3 or lower or one that doesn't speak any language.

An Intellect Devourer meets the Intelligence requirement, but does an Intellect Devourer speak a language? The languages part of its stat block reads:

Languages Deep Speech understands but can't speak, Telepathy 60 ft.

This seems cut and dry: it says right there that it knows Deep Speech but cannot speak. But I feel that the situation is not that straightforward.

This situation seems similar to a wizard with their tongue cut out. With no tongue, they cannot speak. They have the mental ability to speak, but they lack the physical ability to do so without some magical or mechanical help.

I feel that an Intellect Devourer is in the same situation. When it uses its Body Thief ability to control a victim, it can speak through their mouth - as confirmed by an official D&D 5e product:

It's confirmed by Meloon Wardragon's stat block in Waterdeep: Dragon Heist (p. 210). His languages are shown as "Common, Deep Speech, Telepathy 60 ft." It does not contain the "but can't speak" portion found in the intellect devourer's stat block, but does contain the Deep Speech and Telepathy from the intellect devourer, which makes clear that the stats shown are for the infested version of Meloon.

The intellect devourer possesses the mental ability to speak, but its natural form lacks the physical means of doing so without the help of a host body.

So does Detect Thoughts work against an Intellect Devourer?

Answer 1

Possibly

It is reasonable some creatures can think in words without being able to speak it (like a muted wizard) and there might be creatures that understand words magically without thinking in them (a golem might be an example), and it'd be reasonable to allow the spell to work on the former, but not the latter.

That said, the meaning of the word 'speak' can be ambiguous. Depending on how mechanical or actual the word's use is, it could mean that a mute wizard is not a valid target, or that a parrot is a valid target.

Sadly, the RAW is silent on this, at least from what I've found.

So, ask your DM.

Or possibly customer service or one of the Twitter accounts that sometimes give rules clarifications.

Answer 2

By Strict Raw: No

The Intellect Devourer cannot "speak" and instead communicates via telepathy.

Telepathy

Telepathy is a magical ability that allows a monster to communicate mentally with another creature within a specified range. The contacted creature doesn't need to share a language with the monster to communicate in this way with it, but it must be able to understand at least one language. A creature without telepathy can receive and respond to telepathic messages but can't initiate or terminate a telepathic conversation.

Since Telepathy is not strictly stated as speaking, nor is it described as a form of speech. I would even further point that since telepathy doesn't require both subjects to know each other's language to work, just that they know "a" language, you aren't necessarily speaking in words in telepathy.

The more fluffy way of describing this then is that you cannot read the Thought Devourer's thoughts because its method of thinking is too foreign to your own.

My personal thoughts as a DM:

This would need to be ruled on a case by case basis. I think it makes sense you cant read an Intellect Devourer's thoughts. They are likely not language based, and are very foreign to how "we" think.

I would apply some older versions of D&D Detect Thoughts. The Intellect Devourer, while you wouldn't be able to locate it, you could pick up some of its surface emotions/instincts. You could tell if it's hunting something. You could tell if it is angry. Things like that.

At the same time though, the very strict raw definition also means if a wizard cuts out his larynx, he cant be targeted, because he "cannot speak", which is just kind of nonsense.

So the key here is to really understand that RAW is never something that you as a player or DM should follow blindly. Instead it's generally a "talk to your DM and see what they are okay with" type deal. In this case, you made a pretty sound argument for me to allow at least some level of thought detection in my games.