When do you use ability checks without a specific skill?

Question

When, if ever, as a DM would you ask players to make an ability check without allowing them to apply a skill proficiency?

The Player's Handbook (p. 174) says:

The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results. For every ability check, the DM decides which of the six abilities is relevant to the task at hand

and

Sometimes, the DM might ask for an ability check using a specific skill

The following section on using each ability lists other checks that aren't named under specific skills. Are these tasks (e.g. Forcing open a stuck, locked, or barred door or breaking free of bonds) ineligible for gaining proficiency?

Answer 1

When certain spells or other game effects request skill-less checks

As pointed out by Someone_Evil, certain spells, such as entangle, dispel magic, telekinesis, etc, require ability checks to use or escape them, and these ability checks do not specify a skill.

Dispel magic:

For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a successful check, the spell ends.

Entangle:

A creature restrained by the plants can use its action to make a Strength check against your spell save DC. On a success, it frees itself.

Telekinesis:

Make an ability check with your spellcasting ability contested by the creature's Strength check. If you win the contest, you can move the creature...

When rolling Initiative to determine your order in combat

There's also Initiative rolls (thanks Greenstone Walker), which is technically a Dexterity ability check, although because it has it's own name ("Initiative"), it's often not called that. Initiative is described in the basic rules under the Order of Combat section:

When combat starts, every participant makes a Dexterity check to determine their place in the initiative order.

Although you cannot add your proficiency bonus to it, there are other bonuses you can add to it.

When you make an ability check using a tool proficiency

As pointed out by V2Blast, "ability checks relating to a tool do not have any skill associated with them, because whether you add your proficiency bonus to the roll simply depends on whether you're proficient with the given tool. The most obvious example in the rules is thieves' tools, which you can use to make a Dexterity check to pick a lock/disarm a trap; that's not associated with any skill, but you can still add your proficiency bonus depending on whether you're proficient with the tool."

From the basic rules on Tools:

Proficiency with a tool allows you to add your proficiency bonus to any ability check you make using that tool. Tool use is not tied to a single ability, since proficiency with a tool represents broader knowledge of its use. For example, the DM might ask you to make a Dexterity check to carve a fine detail with your woodcarver's tools, or a Strength check to make something out of particularly hard wood.

In other words, using a tool you're proficient with is just an alternative way to add your proficiency bonus vs. making a skill check. Either way, it will be a kind of ability check that uses one of your six ability scores (but not necessarily always the same one, as mentioned in the above quote) and optionally your proficiency bonus if you're using a skill or tool set that you're proficient with.

When the DM otherwise decides that none of the existing skill or tool proficiencies apply to the particular check

Without wanting this to turn into a list of every example I can think of, basically, when there are situations that call for an ability check, using one of the 6 ability scores, but the nature of the check doesn't really relate to a specific skill (or tool set, as per the above section).

In such scenarios the DM would ask for an "Intelligence check", for example, rather than, say, "Intelligence (History)" (or more commonly just "History"). In practice, associating an ability check with a skill just allows the player to be able to add their proficiency bonus if they are proficient in that skill, so an ability check without an associated skill (or tool) simply wouldn't include your proficiency bonus.

As an example that I've seen other DMs use, a DM might ask for an Intelligence check to see if your character can remember something that happened last week. Of the five skills normally associated with Intelligence (Arcana, History, Investigation, Nature, Religion), none of those really apply (History is the closest, but that's more to do with having studied history, not simply remembering something from the recent past).

Another example that I've seen is whether a not very intelligent character can think of a plan that the player (who is more intelligent that their INT 8 character) has thought of, to see if that character was able to have the brainwave necessary to think of it. These sorts of ability checks can literally be as arbitrary as that, depending on the DM.

Answer 2

By default, you can't gain proficiency in efforts that aren't relevant to a skill, saving throw, or tool

There are no official ways, as far as I know, for gaining proficiency in generic ability checks. You can have proficiency in tools, saving throws, and skills which add the Proficiency Bonus to an ability check when applicable, but otherwise the generic ability checks will not incorporate the Proficiency Bonus.

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However, the Dungeon Master's Guide contains a few variant rule that changes how skill proficiency works, one of which is:

Ability Check Proficiency

With this variant rule, characters don’t have skill proficiencies. Instead, each character has proficiency in two abilities: one tied to the character’s class and one tied to the character’s background. The Ability Proficiencies by Class table suggests a proficiency for each class, and you choose which ability is tied to a given background. Starting at 1st level, a character adds his or her proficiency bonus to any ability check tied to one or the other of these two abilities.

With this variant, you would have proficiency in any ability check tied to your proficient ability.

Personally I find that this variant makes the game less interesting as characters of the same class get less opportunity to specialize based on skill proficiency. That being said, it is a simplified skill system which may help newer players get used to D&D.

Answer 3

D&D 5e distinguishes combat and out-of-combat use of skill proficiencies.

In combat, it's usually "Ability (Skill)" check

Combat rules always mention a specific skill when talking about ability checks — Strength (Athletics), Dexterity (Acrobatics), etc. Spells usually require a saving throw to resist their effects.

There are a bunch of spells, though, which explicitly require to make an ability check without any proficiency applied. These spells include counterspell, entangle, telekinesis, maze, dispel magic, Evard's black tentacles, wrathful smite, ensnaring strike, magnify gravity, Otiluke's freezing sphere, immovable object, detect thoughts, web, ravenous void, whirlwind, and probably more. They all mention an exact check in their description, so there's no ambiguity here.

Out of combat, it's up to the DM

Freeform ability checks are a DM's tool and used completely at the DM's discretion. The rules do not dictate the usage of dice anymore. The DMG allows us not to use dice out of combat at all (p. 236):

One approach is to use dice as rarely as possible. Some DMs use them only during combat, and determine success or failure as they like in other situations.

The DMG also says that the DM can "feel free to change or ignore rules" when the game is not combat-focused to enhance immersive storytelling (p. 34):

Since combat isn't the focus, game rules take a back seat to character development. Ability check modifiers and skill proficiencies take precedence over combat bonuses. Feel free to change or ignore rules to fit the players' roleplaying needs, using the advice presented in part 3 of this book.

Generally speaking, you add your proficient bonus when you are proficient in this specific course of actions. Different characters with different backgrounds has different areas of expertise. Skill list is one of the possible ways of defining such a difference, but not the only one.

A prominent option that doesn't use the skill list at all is the "Background Proficiency" variant rule (p. 264):

With this variant rule, characters don’t have skill or tool proficiencies. [...] Instead, a character can add his or her proficiency bonus to any ability check to which the character's prior training and experience (reflected in the character's background) reasonably applies.