Circle Magic & Cantrips

Seen a bit of discussion on this and just looking for confirmation.

Can you use Circle Magic with a Cantrip? Say Mend in order to Mend more?

I see a lot of people saying No because they don't use Spell Slots. But other are arguing that you can Upcast a Cantrip and use Circle Magic that way.

Thoughts? 

Per the rules:

"Any spell that has a casting time of an action or 1 minute or longer and is cast using a spell slot can be cast as a Circle spell."

Cantrips are not cast using a spell slot, and are therefore ineligible.

RWinnie is correct, but it's also worth pointing out that you cannot "upcast a cantrip".

The term "upcast" refers to casting a spell with a spell slot of a level higher than the spell's level. The rules do not define any means of doing this with cantrips, nor would there be any reason to do so, because cantrips don't have upcasting benefits.

That's wrong. It's not possible to upcast a spell that doesn't use a spell slot: cantrips, rituals, special abilities that let you cast specific spells without a spell slot, or magic items.

Casting without Slots

There are several ways to cast a spell without expending a spell slot:

Cantrips. A cantrip is cast without a spell slot.

Rituals. Certain spells have the Ritual tag in the Casting Time entry. Such a spell can be cast following the normal rules for spellcasting, or it can be cast as a Ritual. The Ritual version of a spell takes 10 minutes longer to cast than normal, but it doesn’t expend a spell slot. To cast a spell as a Ritual, a spellcaster must have it prepared.

Special Abilities. Some characters and monsters have special abilities that allow them to cast specific spells without a spell slot. This casting is usually limited in another way, such as being able to cast the spell a limited number of times per day.

Magic Items. Spell Scrolls and some other magic items contain spells that can be cast without a spell slot. The description of such an item specifies how many times a spell can be cast from it.

Using a Higher-Level Spell Slot

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell takes on the higher level for that casting. For instance, if a Wizard casts Magic Missile using a level 2 slot, that Magic Missile is level 2. Effectively, the spell expands to fill the slot it is put into.

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.

There's an answer about this topic in the 5.5e SAC:

What level is a spell if you cast it without a spell slot?

Unless the text says otherwise, a spell cast without a spell slot is cast at its lowest possible level, which is the level that appears in its description.

An example of an exception to this is often found in monster stat blocks. A monster with the Spellcasting action may have spells listed with a “(level # version)” parenthetical. This means the spell is still cast without a spell slot, but its effects are equivalent to a version of the spell cast using a spell slot of the specified level.

You literally quoted the basis of my argument in your reply:

Using a Higher-Level Spell Slot
When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell takes on the higher level for that casting. For instance, if a Wizard casts Magic Missile using a level 2 slot, that Magic Missile is level 2. Effectively, the spell expands to fill the slot it is put into.

Cantrips are 0 level spells. If you want to spend a a level 1 spell to make a Cantrip into a level 1 spell, it doesn't do anything other than make it count as a level 1 spell instead of a level 0 spell, but that should meet the requirements of Circle Magic. 

I can't imagine how Circle Casting a Cantrip, that you are spending a spell slot on to cast, can be any more troublesome than normal Circle Magic?

Cantrips. A cantrip is cast without a spell slot.

---

EDIT: anyway, you can rule it that way, but IMO, it's neither RAW nor RAI. If you're interested, the following threads are also about this:

Quote from erikmholmes >>

You literally quoted the basis of my argument in your reply:

Using a Higher-Level Spell Slot
When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell takes on the higher level for that casting. For instance, if a Wizard casts Magic Missile using a level 2 slot, that Magic Missile is level 2. Effectively, the spell expands to fill the slot it is put into.

Cantrips are 0 level spells. If you want to spend a a level 1 spell to make a Cantrip into a level 1 spell, it doesn't do anything other than make it count as a level 1 spell instead of a level 0 spell, but that should meet the requirements of Circle Magic. 

I can't imagine how Circle Casting a Cantrip, that you are spending a spell slot on to cast, can be any more troublesome than normal Circle Magic?

In order to cast a spell with a spell slot of any level, the spell must be prepared. Cantrips are not prepared, they are known.

Artificers, Bards, Clerics, Clerics, Druids, Sorcerers, Warlocks, and Wizards all have "Cantrips. You know [two to four] cantrips of your choice from the [class] spell list."

It's not that Cantrips can be cast without a spell slot, it's that they are always cast without a spell slot. You do not have the option to ever cast a Cantrip with a spell slot.

What page does it say that on?

Quote from erikmholmes >>

What page does it say that on?

The class spellcasting feature for every class that can cast Cantrips.