Can divine smite be non lethal?

Question

One of my players is arguing that he can knock another creature unconscious instead of killing them when using divine smite when it causes the creatures hp to fall to 0 or lower. I have already ruled in my campaign that it can't be declared as non-lethal, but I wanted to see if I made the right call.

Answer 1

The rule for knocking a creature out is as follows:

Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.

So the rule is, if you want to knock a creature out, you have to reduce them to 0 hit points with a melee attack. That's the only restriction given; it doesn't even say melee weapon attack.

Divine Smite: Starting at 2nd level, when you hit a creature with a melee weapon attack, you can expend one paladin spell slot to deal radiant damage to the target, in addition to the weapon's damage.

Divine Smite can only be applied on a melee attack. Note that it's phrased as being additional damage to the weapon's damage, rather than, for example, entirely separate damage that just happens to appear at the same time as the weapon attack. This means that its damage is dealt by a melee attack, so yes, you can knock a creature unconscious with Divine Smite.

Answer 2

Since you have already ruled that this is an impossibility in your campaign, my answer may be redundant, but I wanted to provide a counter point to the above answer of it being allowed; to show why it might be argued as disallowed. (Also because @Miniman encouraged me to challenge his answer.)

Here is a link to a former question dealing directly with 'Divine Smite' being considered 'extra damage' for the purposes of burst/nova damage as some are calling it.

The relevant description from Divine Smite is as follows:

"...to deal radiant damage to the target, in addition to the weapon's damage. The extra damage is 2d8 + 1d8 per Spell Slot level above 1, to a maximum of 5d8.

Divine Smite, and it's utilization of a spell slot to pull magical energy from to cause, very suddenly, the radiant damage to burst in addition to the weapon damage is what I believe makes it an impossibility to knock someone out with it. That would be saying I could throw on Searing Smite , hit someone with my Warhammer which drops them to 1hp and then when the 1d6 fire damage explodes from my weapon as a result of Searing Smite, dealing it's full damage and potentially outright slaying a creature with only 4 max HP for example; I say I only wanted to knock it unconscious.

I don't have that option (as far as I'm aware). Searing Smite would deal it's full 1d6 damage regardless of my intentions. If I wanted to knock a creature out and my first attack only took them 1, I'd have to swing again, or wait until I could, and be cautious not to kill it with anything other than a melee attack.

Answer 3

Building on some of the existing answers, and contrary to what some might be making their default assumption, this judgement is not only correct, but there is actually a large subset of magical abilities which qualify for the incapacitate criteria 100% if we go RAW.

As Miniman mentioned, for knocking out a foe:

Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.

The point to note here is that is states you can do this with a melee attack, not a melee weapon attack, attack action, or any other similarly limiting action. If we then cross-reference the Combat section of the PHB, under "Melee Attacks" it also explicitly nods to spells

Used in hand--to--hand combat, a melee attack allows you to attack a foe within your reach. A melee attack typically uses a handheld weapon such as a sword, a Warhammer, or an axe. A typical monster makes a melee attack when it strikes with its claws, horns, teeth, tentacles, or other body part. A few Spells also involve making a melee attack.

If we take this into consideration, then RAW:

Directly tying back with Divine Smite, he is making a melee attack, so at this point he chooses to make it a blow that incapacitates.

If he was using Thunderous Smite too, he starts concentration, and when he makes a melee attack deals extra damage, choosing to make that an incapacitating melee attack.

If he is a paladin/ranger multiclass and is using Hunter's Mark, and makes a melee attack that deals extra damage he can elect to make it an incapacitating strike.

If he was also then making a melee attack as part of Casting a Spell such Greenflame Blade, since he is making a melee attack he can choose for the target of the melee attack to be incapacitated (the other fellow is not so lucky).

If his wizard companion grabbed a peasant with Shocking Grasp, he is making a melee spell attack and can elect to incapacitate the unwitting serf.

Answer 4

Divine Smite is not magical, do not confuse having to utilize spell slots with explicitly stating the ability is magical or uses magical energy. In order for an ability to be determined as magical, it must be explicitly stated as such. Divine smite is not.

The wording for Divine Smite (PHB p85) in doesn't specifically indicate that is magical in any way, nor does the description of Spell Slot usage make it magical (PHB p201) thus it is not magical.

Refer to a separate post for more on this

Does Improved Divine Smite work in an Antimagic Field?

In addition, the damage is added to a 'melee' attack, it is not a separate spell attack. The damage is considered added to the weapon and not a separate effect. All smites damage would,by rules, be allowed to use to knock out a creature since they are part of the melee attack. INCLUDING SEARING SMITE. The damage happens at the same time as the attack and for the purpose of knocking out the creature there is no distinction between them. They both come from a melee attack. I will not quote specific rules requiring melee attacks as they are well documented above.

To be clear, this notion that I can use Divine Smite or Searing Smite to knock a target out doesn't however prevent the user from further damage that may be a part of the initiating effect. For example, if I set the target on fire with searing smite

PHB 274) - The next time you hit a creature with a melee weapon attack during the spell's duration, your weapon flares with white-hot intensity, and the attack deals an extra 1d6 fire damage to the target and causs the target to ignite in flames. At the start of each of its turns ... on a failed save it takes 1d6 fire damage...

The user falls unconscious on the turn I used Searing Smite, but they also ignite in flames.

If noone puts them out,on their turn, they will take 1d6 fire damage from the flames (not a melee attack) and die or start making death saving throws.