Can Thieves' Cant be understood without a level in Rogue?

Question

The Player's Basic Rules and Player's Handbook describe the Thieves' Cant class feature as:

... a secret mix of dialect, jargon and code allows you to hide messages in seemingly normal conversation. Only another creature that knows thieves' cant understands such messages. It takes four times longer to convey such a message than it does to speak the same idea plainly.

In addition, you understand a set of secret signs and symbols used to convey short, simple messages, such as whether an area is dangerous or the territory of a thieves' guild, whether loot is nearby, or whether the people in an area are easy marks or will provide a safe house for thieves on the run. [Emphasis added] (PBR, p. 27; PHB, p. 96)

Thieves' Cant and Druidic are described as secret languages that can be taken with the DM's permission (PBR, p. 34; PHB, p. 123), but there is no other mention (other than being a rogue) of how to understand Thieves' Cant, whereas Druidic and the written ciphers of the Linguist feat specifically state they can be magically deciphered. (PHB, pp. 66 & 167) Since the PHB does not explicitly say so:

Is there any magical way a non-rogue could understand Thieves' Cant?

The spell Comprehend Languages allows the caster to "understand the literal meaning of any spoken language ... [and] any written language [while] touching the surface on which the words are written. ... [but] This spell doesn't decode secret messages in a text or a glyph, such as an arcane sigil, that isn't part of a written language" [Emphasis added] (PBR, p. 86; PHB p. 224) while the spell Tongues grants "the ability to understand any spoken language ..." (PHB, p. 283).

The warlock's Eyes of the Runekeeper eldritch invocation simply states, in its entirety, "You can read all writing." (PHB, p. 111)

Are the "hidden messages" and "secret signs and symbols" of Thieves' Cant considered a "language" or "writing" per the above spells or invocation?

On re-reading the PHB, I stumbled across the following under "Languages" in Chapter 4, "With your DM's permission, you can instead choose a language from the Exotic Language table or a secret language, such as thieves' cant or the tongue of the druids." (PHB, p. 123) So it appears that 1) you can gain understanding without being a rogue, and 2) it is considered a language in general; but, is it for magical deciphering purposes?

Answer 1

Thieves' Cant isn't a written language, thus there would be nothing to understand via a spell.

Nowhere in the quote you've pulled (or the PHB) is thieves' cant ever described as a written language. This is because thieves' cant is both verbal and physical communication. Some word substitution (1 to 1) is used, but it is largely based on metaphor and contextual meaning and a big part of this is the hand symbols used when speaking. D&D's basis for thieves' cant is both historical and a trope.

The symbols mentioned are more like pictographic signs than words.

As such they are not translated, but identified, similar to how we use symbols such as the biohazard sign and nuclear sign to signify specific danger or how the symbols on a crosswalk signify when to wait and when to go. The closest living example of this I can highlight would be Hobo symbols that survive and are still in use today in the US. Different symbols would mean different things to different groups and insider knowledge for understanding thieves' cant symbols would be a must.

Answer 2

As stated in your excerpt from the players' handbook, thieves cant isn't realy a language unto itself, but a way to put hidden messages into an existing one. As such, using comprehend languages or tongues would allow you to understand the language being used, but not the message hidden in thieves' cant.

Think for example, someone saying 'I need to see a man about a dog'. If you don't speak english, you can use those spells to understand what was said, but you still don't know what is actually meant by it.

Something like detect thoughts however, probably would let you know what the guy using thieves' cant is trying to say.

Answer 3

Per the description of the "Training" downtime activity in the rules:

You can spend time between adventures learning a new language or training with a set of tools. Your DM might allow additional training options.

First, you must find an instructor willing to teach you. The DM determines how long it takes, and whether one or more ability checks are required.

The training lasts for 250 days and costs 1 gp per day. After you spend the requisite amount of time and money, you learn the new language or gain proficiency with the new tool.

If you wanna learn Thieves' Cant and/or Druidic and you have a Rogue or Druid in your party, ask him if he wants to teach you. Things that you know can be taught to party members.

Like in the campaign I do, we got a magical trident and a Bard wanted to use it. Without martial training he can't efficiently use it, so now I as a Fighter that had martial training teaches him in free time how to use a trident.

The same can be done for language proficiencies, or anything really. Just make sure you find someone that knows it.