Can you gain a proficiency bonus, without being proficient?

Question

I'm asking with a particular eye on the Rogue's level 11 feature, "Reliable Talent":

Reliable Talent

By 11th level, you have refined your chosen skills until they approach perfection. Whenever you make an ability check that lets you add your proficiency bonus, you can treat a d20 roll of 9 or lower as a 10.

The obvious application is to skills/tools you are proficient in. However, the wording doesn't mention proficiencies specifically. Does anything other than proficiency allow you to add your proficiency bonus to an ability check?

Research:

The Bard's "Jack of all Trades" feature allows you to add half of your proficiency bonus. Not enough to trigger Reliable Talent, however. (Possible follow-up question: If something else also gave half of your proficiency bonus to the check, would you then trigger Reliable Talent? Is there anything else that gives you half of your proficiency bonus?)

Answer 1

Yes

But probably not in the way you're hoping.

You can gain a proficiency bonus from Jack of All Trades on skills you wouldn't otherwise be proficient in.

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However

it's been clarified that any individual check that benefits from Jack of All Trades does not benefit from Reliable Talent.

This was clarified in the 2019 Sage Advice Compendium, which is quite clear: These aren't allowed to work together on a single check.

Can the rogue’s Reliable Talent feature be used in conjunction with Remarkable Athlete or Jack of All Trades?

No. Each of these features has a precondition for its use; Reliable Talent activates when you make an ability check that uses your proficiency bonus, whereas the other two features activate when you make an ability check that doesn’t use your proficiency bonus. In other words, a check that qualifies for Reliable Talent doesn’t qualify for Remarkable Athlete or Jack of All Trades. And Remarkable Athlete and Jack of All Trades don’t work with each other, since you can add your proficiency bonus, or any portion thereof, only once to a roll.

Answer 2

The second level Channel Divinity feature of the Knowledge Domain for Clerics, Knowledge of the Ages, grants proficiency with a skill or tool for ten minutes (PHB, p. 59). If a character had this ability and also Reliable Talent, they would gain the benefit of Reliable Talent when making ability checks using this temporary proficiency.

Technically this is not "adding the proficiency bonus without having proficiency" because for the duration the character does have proficiency, but it's different enough from the usual ways to gain proficiency that it seemed worth noting in this context.

As a side note, the Jack of All Trades feature for Bards also specifies that it applies to ability checks where you do not add your proficiency bonus. I believe this to be defensive language to prevent unintended stacking should a method to add proficiency bonus without granting proficiency ever be added to the game.

Answer 3

The phrase

Whenever you make an ability check that lets you add your proficiency bonus

says it all, really. It doesn't matter if that bonus is halved, doubled or straight up; if you add it, then Reliable Talent kicks in.

However, this is not as overpowered as some comments seem to suggest. First, it only applies to ability checks - not attack rolls or saving throws (note, however, that initiative is an ability check so it applies to that). Second, it only has a possible effect where the target number (DC - Bonus) is 10 or less - if you need to roll more than 10 then it won't help you. At the level where this kicks in these rare pretty trivial DCs - a challenge with a DC of say 20 or above is indifferent to this for half proficiency.

To elaborate, an 11th level and up character has a proficiency bonus of +4 to +6 and a maximum stat bonus (without magic or barbarian strength) of +5. This gives a total bonus for half proficiency of +7 to +8. If you do as recommended and set DCs in multiples of 5, reliable talent simply makes DC10 certain (up from 90 or 95%) and DC15 certain (up from 65 or 70%) and has no effect on DC20 or higher.