What justification could there be for a PC learning thieves' cant when multiclassing Rogue?

Question

In our campaign, I'm currently considering multiclassing into Rogue very soon. One thing I'm wondering is how, if at all, it could be justified for me to learn thieves' cant when our party is currently alone in the middle of an illusory mind-dungeon - the point being that there are no Rogueish role models or tutors or any of the like for it to make sense for me to suddenly be able to learn independently a language that is currently known and used by others.

If such a justification can't be found, should our DM simply deprive me of this ability? My instinctive response is that it would feel like an unfair disadvantage based on a roleplay-founded issue (although I'm fully aware that its use is entirely dependent on the world/DM - this is more of a principles question, though still a situational one).

What should happen in this situation? What about if it is impossible by any non-divine means to learn the language?

Answer 1

Choose whatever narrative you like best. Class features do not need narrative justification.

The D&D 5E system is mainly driven by rules and abstractions rather than narrative. Regardless of the narrative you use to explain how your character gained their class features, your character will gain those class features because the rules say they do.

Multiclassing into Rogue means you gain a 1st level Rogue's class features, plus proficiency with light armor, thieves' tools, and one extra skill. From the PHB section on multiclassing:

When you gain a new level in a class, you get its features for that level.

So by taking that level in Rogue, you can provide whatever narrative explanation you want. Maybe your character finds a book containing Thieves Cant terminology. Or maybe they've been studying it all along, and they weren't fluent until recently. Maybe they suddenly remember some past experience to explain their Expertise and Sneak Attack. The game assumes that any story will make sense. Your character gains these features because the D&D 5E rules say so.

D&D is designed to follow game mechanics rather than realism.

And trying to impose narrative realism into D&D is often unproductive when it clashes with those mechanics. Fantasy elements aside, class progressions often mean that characters gain new abilities in ways that may be inconsistent with the narrative.

Example: Wizards learn spells through study and research. After gaining sufficient combat XP, the Wizard gains a level and add two new spells to their spellbook. This is an abstraction. Even if they're in a dungeon, it is assumed that the Wizard found the time and resources to write those new spells. Why? Because that's what the system rules say. The DM could encourage the Wizard's player to provide some narrative for roleplay sake, but it should not be a requirement.

There is no "correct" explanation for how a character gets their class features. Some players may want to roleplay some ritual or process of gaining their new powers. Other players may prefer to ad-lib a brief explanation of how they got their abilities when nobody was looking. Other players may skip an explanation entirely.

What about Rule Zero?

The DM has the final say regarding what happens at the table and in their story. In theory, the DM could declare that a character doesn't gain their class features. But this selective realism so puts the player at a disadvantage, and would likely seem unfair. If your DM is trying to run a narrative-driven game, then it may help to discuss this with your DM outside of the game, and agree to a method and explanation for gaining your class features.

Answer 2

Class levels are abstract

The character does not know that he just took a level in rogue, he has always been studying and practicing rogue things and is only now confident in his own ability to put it into practice.

In short he has always known basic thieves' cant, but maybe he struggled with his memory and something innocuous triggers inside him and it all falls into place. That happens all the time - when you stop concentrating on a problem the answer comes to you.

Example: A scratch on the wall looks suspiciously similar to a symbol in thieves cant, the rogue stares for a while and remembers back to being taught it by an acquaintance long ago. He had completely forgotten about it until that moment.

This is similar to magic, a wizard doesn't suddenly know level 2 spells and immediately add them to the spell book, they have always been in the book and the wizard has been trying to cast them unsuccessfully for 2 levels, and gets the breakthrough at that key moment.

To add some good subjective to this:

I run my own campaigns in this style, I find it incredibly immersion breaking that things suddenly happen, and most of my players do as well. My ranger player for example is still waiting for a long enough break to find her animal companion, and being without has helped the players bond with the world far better than having a random passing animal just at that key moment.

Answer 3

Narratively? None at all. RAW? The knowledge just appears

RAW doesn't care about making any kind of sense narratively, and there is no way the designers could design around narratives that exist only at individual tables and still keep a tight ruleset. You would just mysteriously pick up the knowledge, if you can ignore the provenance of that knowledge.

However, your GM could reasonably have you hold off on that level change until some narrative element justified it. This is more in line with the Milestones approach, where you wouldn't level in the middle of a dungeon anyway.

Frankly, this is a question for your GM. No one here can know what your character's or game's circumstances are to give you a definitive answer. But, if you want some spitballing ideas off the top of the head, here you go:

• If your character is a servant of a god of trickery or knowledge, they might divinely bless you with your level and features for their own mysterious purposes.
• There might be a magic tome of some sort found in a chest or on a shelf that could imbue you with the class features found in a chest somewhere.
• Some high-level person in the next dungeon over might have cast Wish and your getting that Rogue level and its class features might serve that wish in some way down the road.
• You are in an illusory mind-dungeon. Maybe the nature of the place ties it in with the Astral Plane, and some astral fragment floats into your head with the knowledge, or is placed there by some entity.
• Maybe later on in the campaign or after, far in the future, you find a Ring of Wish or draw the Moon in a Deck of Many Things, or something like that, and cast Wish from it, wishing that you had learned to be a rogue back in time when you were at your current level, and boom, there it is. It's mysterious now, but it will come full circle and all come clear eventually.

Answer 4

First, discuss with your DM

When you have questions like this of "should this be allowed" the DM will ultimately be the final authority. So, you should talk to them about your concerns. D&D 5e is a game about collaboratively storytelling, so they will typically work to weave it into their narrative, or overlook it for the sake of sticking to the mechanics. Every game I have ever played in had a Session 0 which discussed expectations surrounding multiclassing and narrative-driven vs. mechanics-driven gameplay. It really needs to be worked out with the DM as they will be able to offer suggestions of how it would fit in the narrative.

Self-regulate

The book says you can multiclass, so I doubt any DM would flat out say "no", but if you are worried about breaking the narrative you can always multiclass but choose not to use Thieve's Cant until you feel it is narratively justified. If you haven't already in preparation to multiclass, you can have your character begin researching and learning about thieves guilds and the like.
In my current game, I avoid taking Touch spells due to germaphobia. As a Sorcerer, I recently added a couple Touch spells because I expect to be over the germaphobia before the end of my current level, but I am choosing to not use those spells until they feel narratively justified (our group has been going with heavy story driven RP). It is far from optimized gameplay, but it enhances the RP experience for me and has been more enjoyable than mechanics-driven games I have played in the past.