[RPG] cast cantrips using spell slots to get a more potent effect?


I am wondering whether I could cast a cantrip, for example Thaumaturgy, using a spell slot to get more than a single effect of the cantrip (i.e. both ominous sounds and alter appearance).

Best Answer

No you cannot (With a potential loophole for Warlocks)

Each class spellcasting description specifically describes what its slots can be used to cast.

The Wizard, Bard, Druid, Cleric, Eldritch Knight, Arcane Trickster, Sorcerer and Ranger classes all say:

The [class] table shows how many spell slots you have to cast your spells of 1st level and higher.

In these cases, the class feature actively prevents you from casting anything other than 1st level spells or higher with your slots. Since cantrips are 0th level, you can't use one of these slots to upcast a cantrip because these class feature rules are more specific than the general rules on spellcasting.

But what about a multiclasses character?

The multiclass rules say:

Each spell you know and prepare is associated with one of your classes, and you use the spellcasting ability of that class when you cast the spell.

meaning that even when you multiclass and cast a spell, you are still limited by the spellcasting feature as defined by the class that it's associated with, with the exception of the number of spell slots you have.

Okay, so how about paladins?

The Paladin spellcasting section and Warlock pact magic feature say:

To cast one of your [class] spells of 1st level or higher, you must expend a slot of the spell’s level or higher

Paladins don't have cantrips normally, so the only way to get one RAW would involve multiclassing (which we know wouldn't work), or the magic initiate feat. However, the magic initiate feat associates the learned cantrips with a different class. And since the paladin's spellcasting feature explicitly only gives you slots to cast paladin spells, you couldn't use them on a cantrip.

What about Warlocks then?

Technically the pact magic feature doesn't explicitly say that you can't cast a warlock cantrip at a higher level. But there really isn't a point to it. No cantrip to date explicitly says that it has any extra effects what cast with a spell slot, and it is a spell's definition that tells you how the spell reacts to higher level casting. Additionally, the concept of allowing a certain action because there is no rule specifically against it might not sit well with some DMs, as it can open up some doors to some...unintended consequences.

Additionally, Jeremy Crawford, the lead rules designer, has shed some light on this topic saying:

No, since cantrips don't use spell slots.

Even if you don't think JC's word is law, it does provide some insight on designer intent. So, even though a DM might technically, with a liberal ruling, allow cantrips for warlocks to be cast using spell slots, doing so is counter to designer intent, doesn't provide any defined benefit, and isn't a sure thing since it relies on a method of reading rules that actively exploits loopholes.