Can a cantrip be cast using a higher-level spell slot?

Question

Can a cantrip be cast using a higher-level spell slot?

Specifically, I'm thinking of casting Shocking Grasp as a 1st-level spell, to trigger the Storm sorcerer's Heart of the Storm feature (Sword Coast Adventurer's Guide, p. 137):

[...] whenever you start casting a spell of 1st level or higher that deals lightning or thunder damage, stormy magic erupts from you. This eruption causes creatures of your choice that you can see within 10 feet of you to take lightning or thunder damage (choose each time this ability activates) equal to half your sorcerer level.

Answer 1

No. There is a specific unofficial tweet from Jeremy Crawford on the matter:

@JeremyECrawford like most spells can a known cantrip be cast at a higher spell slot lvl. Aka sacred flame lvl 1 for 2d8 radiant dmg
— redwoodguardian (@redwoodguardian) August 24, 2015

No, since cantrips don't use spell slots. https://t.co/MKpg8oozyf
— Jeremy Crawford (@JeremyECrawford) August 24, 2015

Answer 2

Spells can take on a higher level when you choose to cast them using a higher level spell slot. Cantrips don't use spell slots, PHB p. 201:

A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance.

As such their spell level is 0 (ibid):

A cantrip’s spell level is 0.

and you can't cast them at a higher level.

Answer 3

RAW : It's complicated

The rules for cantrips state, emphasis mine :

A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance. Repeated practice has fixed the spell in the caster's mind and infused the caster with the magic needed to produce the effect over and over. A cantrip's spell level is 0.

The argument over whether the emphasised part is a list, whether the "can" implies a possibility only for the first element or for all of them, and all those debates will lead us nowhere, simply because the english language here is ambiguous. So let us focus on other, less ambiguous rule texts that may point us in the right direction.

Take a look at this extract from the rules on Spellcasting for Wizard :

PREPARING AND CASTING SPELLS : The Wizard table shows how many spell slots you have to cast your spells of 1st level and higher.

As stated in the description at the start of this answer, cantrips are level 0 spells. Because of those rules, you can neither "prepare" cantrips (you don't have a cantrip prepared in the first place, you "know" it), nor use your spell slots to cast them.

Moreover, there is also this rule text a bit further :

Vou prepare the list of wizard spells that are available for you to cast. To do so, choose a number of wizard spells from your spellbook [...] The spells must be of a level for which you have spell slots.

Since cantrips are not in your spellbook, you definitely cannot "prepare" them.

This kind of text is found in the spellcasting rules for other classes capable of casting spells. Here are the relevant extracts :

Bard :

SPELL SLOTS : The Bard table shows how many spell slots you have to cast your spells of 1st level and higher.

Cleric :

PREPARING AND CASTING SPELLS : The Cleric table shows how many spell slots you have to cast your spells of 1st level and higher.

Druid :

PREPARING AND CASTING SPELLS : The Druid table shows how many spell slots you have to cast your spells of 1st level and higher.

Fighter (Eldritch Knight Archetype) :

Spell Slots. The Eldritch Knight Spellcasting table shows how many spell slots you have to cast your spells of 1st level and higher.

Paladin :

Oddly enough, Paladin has a slightly different rule text :

PREPARING AND CASTING SPELLS : The Paladin table shows how many spell slots you have to cast your spells.

However, this does not matter since Paladin does not have cantrips in the first place.

Ranger :

SPELL SLOTS : The Ranger table shows how many spell slots you have to cast your spells of 1st level and higher.

Rogue (Arcane Trickster Archetype) :

Spell Slots. The Arcane Trickster Spellcasting table shows how many spell slots you have to cast your spells of 1st level and higher.

Sorcerer :

SPELL SLOTS : The Sorcerer table shows how many spell slots you have to cast your spells of 1st level and higher.

... except Warlock is in an odd spot.

Just like Paladin, Warlock has a slightly different text :

SPELL SLOTS : The Warlock table shows how many spell slots you have.

I haven't found anything else in the rule text to either confirm or deny that Warlock cantrips may or may not be used with a spell slot. It seems like for Warlock, we're back at the "what does can mean in this context?" debate, which means that RAW is still unclear for this class specifically.

A possible counter argument

As highlighted by multiple people in comments and chats discussing this topic, the rules on upcasting spells states the following :

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. [...] Effectively, the spell expands to fill the slot it is put into.

If a cantrip was successfully cast using a spell slot, because of this rule, its level would become the one of the spell slot used, and it would be possible to use it with a spell slot.

However, for the spell to assume this higher level, it needs to be cast successfully in the spell slot. The rule mentioned for each class only allows you to use spell slots to cast spells of 1st level and higher, which cantrips, being level 0, do not qualify.

For a spell to be upcast and assume a higher level, it needs to be cast in a spell slot. But to cast a spell in a spell slot, you need it to be 1st level or higher. In the case of a level 0 spell, the snake bites its tail, and it is effectively impossible to upcast a cantrip.

The issue of "When"

It has been brought to attention that this last text also has an issue with the ambiguity of english language.

This phrase is formatted as "When X happens, Y happens". I naturally interpreted that as cause-consequence : if X happens, then it causes Y to happen. That is why I concluded that if X cannot happen, then Y cannot happen either. However, it would seem that this formatting could also be interpreted as synchronous : if X happens, then Y also happens at the same time.

In that second interpretation, instead of a cause-consequence reading, we have two independant actions happening at the same time. This means that the cantrip could take on the level of the spell slot the instant you cast it, and thus become a "1st level or higher spell". This would then fit the prerequisite for using a spell slot I quoted for most classes.

Both interpretations of this rule text seem valid. In the end, we're back to ambiguous english language.

Conclusion

Both the base rules for cantrips and the specific rules for casting spells for most classes are ambiguous as to whether you can or cannot use a spell slot to cast a cantrip, because the language used can be rightfully read in opposing ways.

What about Rules as Intended?

It seems quite obvious that the intent was that cantrips cannot be cast using spell slots, from the idea itself never being mentioned in the rules, or that all cantrips lack any upcast effect, or even the fact that the situations where this is beneficial are very rare, if they even exist. The tweet quoted in the currently accepted answer, even if unofficial, points in that same direction.

So, should I allow it?

As a DM, I see no good reason to not allow it, although the cantrip itself wouldn't be changed. If the player wants to trigger an effect that depends on the use of a spell slot, they should always be better off using an actual spell rather than a cantrip. But since there's nothing gamebreaking about this, I'd let them go for it.

Answer 4

You can

Cantrips are level 0 spells:

A cantrip's spell level is 0.

You can cast a spell at a higher level:

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level.

This mechanic is called "Casting a Spell at a Higher Level". There is no mention of a requirement for a spell to be using a spell slot. The only requirements is for it to be a "spell" and for it to have a "spell level". The mechanic says that you can use slots of higher level than the spell (eg, 3 is higher than 0) to increase the level of the spell. Why do it?

Consider this example:

If Umara casts light using one of her 3rd-level slots, that light is 3rd level

This would be useful for creating light in Darkness: "If any of this spell's area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled."

Answer 5

Yes

This answer is mostly an aggregate of the other answers, which I think all have components to make the correct answer, but not all pulled together.

Per the cantrip rules, cantrips are specifically defined as having a spell level:

A cantrip's spell level is 0.

By virtue of having a specific level, this creates the opportunity for the rules relating to Casting a Spell at a Higher Level to come into effect:

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level.

Effectively, the spell expands to fill the slot it is put into.

The size of the slot for a cantrip isn't 0 only because there are no level 0 slots, but given that cantrips do have a spell level of 0, any slots used are a higher level.

Circling back to the cantrips rules, there is also this additional relevant language:

A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance. Repeated practice has fixed the spell in the caster's mind and infused the caster with the magic needed to produce the effect over and over.

The phrasing indicates what 'can' be done, but isn't creating an exclusive list.

For comparison, consider the Rogue's Sneak Attack class feature:

Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

Herein, we see language which stipulates an option to the player along with a mandate. A player that his with an attack can deal an extra 1d6 damage, but they must make the attack with either a finesse or ranged weapon.

Also, consider the general rules for Known and Prepared Spells, which states:

Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item.

Again, we see mandatory language being used in the rules.

Language imposing a mandatory requirement is exempt from the language for cantrips. Thus, my Rules as Interpreted is that this suggests it is permissible for a caster to utilize a slot if they so choose, which triggers the final element of the Casting a Spell at a Higher Level:

Some spells, such as magic missile and cure wounds, have more powerful effects when cast at a higher level, as detailed in a spell's description.

The spell's description for a cantrip does have a more powerful effect at a higher level, but it's tied to character level, not spell level. Given this is a general rule for all spells, the more specific rules of the class feature to come into effect because Specific Beats General.

As one final element, the general rules for Spell Slots also supports the notion that cantrips can be used to in larger spell slots as follows:

When a character casts a spell, he or she expends a slot of that spell's level or higher, effectively "filling" a slot with the spell. You can think of a spell slot as a groove of a certain size--small for a 1st-level slot, larger for a spell of higher level. A 1st-level spell fits into a slot of any size, but a 9th-level spell fits only in a 9th-level slot.

The rules specifically describe slots as being grooves of a specific size capable of holding spells whose level is equal or less than them. And since cantrips do have a spell level, they can comport with those requirements.

Answer 6

I think it is clear from all the other answers present that there is no clear and simple answer. I'm new here and not sure why this has been resurrected from so long ago... but I think one simple passage gives a clear understanding of how you should play this.

As a referee, the DM interprets the rules and decides when to abide by them and when to change them.

I consider DnD a game of Three Primary Resources: Time, where unforeseen things can happen. Health, your ability to weather damage and things that are trying to kill you. Resource Management, consider this the small r resources, to the big R Resources that all three comprise. In this case, resources include: features, traits, spells, consumables... in general things the players can use and at least for the moment lose.

If your player is willing to use a Resource, I'm willing to make something happen. Cantrips, often, are simply a passage of time; like using thieves tools.

A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance. Repeated practice has fixed the spell in the caster's mind and infused the caster with the magic needed to produce the effect over and over. A cantrip's spell level is 0.

This implies a character can use them over and over until success, I don't force them to cast it and test it every time. I either limit the number of checks because 'x' or I let it happen. Often having it happen means, I ask the player to roll, that roll gives me something to inform on how long the success takes and then I decide what roll to make in seeing if something unexpected happens. A Random Encounter.

Using a resource is often something that changes these conditions, drastically reducing the time component by using one of the two other resources.

To me, that you want to use a cantrip in combat often results in the lost of health, because you are sacrificing damage that would reduce the length of the combat for the conservation of your spell slots. I'm much happier to see the expending resource go for increased damage that would kill enemies and or intimidate them, and there by use spell slots, a resource and conserves the health. If you wanted to use a cantrip, at first level, and gain the

[...] whenever you start casting a spell of 1st level or higher that deals lightning or thunder damage, stormy magic erupts from you. This eruption causes creatures of your choice that you can see within 10 feet of you to take lightning or thunder damage (choose each time this ability activates) equal to half your sorcerer level.

I would be happy to let that happen.

The D&D Rules help you and the other players have a good time, but the rules aren't in charge. You're the DM, and YOU are in charge of the Game... but to create a ... world that revolves around their actions and decisions.

Their decision to expend a Resource is acceptable. I would let it happen. I would let it proc the ability tied to the spell slot resource expenditure. I would also maintain that a cantrip cast at 1st level, 9th level or 0 level does the same damage. There is no effective reason to cast a cantrip at any level, it is a 0 level spell often effected only by your level.

The spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).

I think there are a lot of other great answers here. I don't think this is a question that the Rules as Written, Rules as Intended, or the Rules as rules need to interact with. This isn't a question about; can I the player argue to every DM I meet that they should let me do this because the rules say it... This is a question far more concerned with; is my DM ready to let me expend a resource I don't need to expend, and don't gain from expending, in order to proc a resource that happens when a expendable resource is expended.