Is there a rule governing how I should factor in different damage types when a player uses a weapon to damage an object? For example, using a dagger or maul on rope rather than a scimitar, or using a long sword to gouge a hole in a sack.
DND 5e – Using a Dagger for Cutting Rope or Poking Holes
damage-typesdnd-5e
Related Solutions
For the purposes of the resistance/immunity example in the original question:
"bludgeoning, piercing, and slashing from nonmagical weapons that aren't silvered"
The "weapons" portion of the example is actually sufficient to know that it does not apply against the example sources of damage, magical or not. The resistance only applies to specific damage type subcategories of weapon damage. None of the given examples are weapon attacks, so this resistance/immunity to damage from weapons does not apply to the given non-weapon examples in the question regardless of what type of damage is being done.
That said, errata has updated most (all?) instances of the given resistance/immunity example in the question to the following:
Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Silvered
(Weapons -> Attacks)
Now it's clearer that the magical status of the attack itself should be considered.
The Sage Advice compendium provides the following checklist for determining if something is considered magical (see also: How do I know if an ability is magical?)
If you cast antimagic field, don armor of invulnerability, or use another feature of the game that protects against magical or nonmagical effects, you might ask yourself, “Will this protect me against a dragon’s breath?”
[...]
Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:
- Is it a magic item?
- Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
- Is it a spell attack?
- Is it fueled by the use of spell slots?
- Does its description say it’s magical?
Since the question's examples are all spells or spell attacks, they fall cleanly under the umbrella of being magical. As such, thorn whip and the initial spell attack of ice knife are considered magical attacks, which clearly bypasses the errataed resistance/immunity text. Damage dealt as an effect of spell that isn't related to a spell attack roll (like the damage of earth tremor) is both magical and not from an attack, so the resistance/immunity text also doesn't apply there.
It's also worth noting that there's currently no such thing as an attack that is both a spell attack and a weapon attack, as noted in answers to a question about how to refer to non-spell attacks.
D&D 3.5e isn't historically representative.
If you look at the picture of the swords in the Player's Handbook, you will find that the longsword is actually a picture of a bastard sword, the bastard sword is actually a picture of a longsword and the greatsword is actually a zweihander. There were no "greatswords" per se, it was just a generalization for D&D to classify big long heavy sword that requires two hands.
The bastard sword, or hand and a half sword, had a standard grip for one hand, but also tapered at the bottom with a hefty pommel that could be gripped by the second hand. If you look, once again at the Player's Handbook, that is the photo used by the longsword.
The longsword, historically, was not a one handed blade. The handle grip was designed for two hands. It was a lot lighter and more mobile than the two-handed sword.
When it comes to one handed swords, once again it is a generalization. The Anglo-Saxon Seax wasn't primarily a stabbing (piercing weapon). It was an edged weapon (slashing) and it has been noted as such due to the lack of handguard. Handguards, not only helped protect the fingers from another attack, but also prevented your hand from sliding up the blade when stabbing.
Look at this "short sword" (seax) from Owen Bush. There is very little to stop your hand from sliding off the grip if a stab is made. That would make stabbing with it less likely. Could you stab? Sure, why not. Is it optimal? No.
Look at this "short sword" (gladius) from Cult of Athena. There is a very pronounced handguard to prevent your hand from sliding forward. Also look at the very prominent piercing tip. That would make slicing with it less likely. Could you slice? Sure, why not. Is it optimal? No.
Reading the short swords description in the Player's Handbook will reveal that it is often used as an off-hand weapon. Due to the piercing nature and the european influence of D&D, the short sword in the player's handbook is most likely modeled after a main gauche.
Look at this main gauche from True Swords. It is a little longer than the typical dagger, with a very very deliberate pointed tip. Main gauches, in historical fencing, were designed to parry and stab in conjunction with a rapier, foil, epee, etc.
The wakizashi, in Oriental Adventures, is listed as having the same characteristics as a masterwork short sword. However, wakizashis were made along with and with similar techniques as the katana. One doesn't need to go far to see the cutting tests with the katana.
Look at this wakizashi from Casiberia. The wakizashi has the slight bend to the blade, emphasizing a cutting edge, rather than a piercing tip. Can you pierce with a wakizashi? Of course. Will it slice better? Absolutely.
Use Houserules for alternatives.
Wanting a thrusting short sword? Style it as a gladius. Want a slashing shortsword? Style it as a seax. Your culture and region of play in-game will determine what weapons are available, in use, and how they are used.
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Best Answer
Yes. See Chapter 8 of the DMG, the section entitled Objects. A partial quote:
The section then goes on to suggest ways of giving AC and HP to objects, as well as taking into account factors such as size, damage types, and thresholds. Less a hard-and-fast rule and more a collection of guidelines.
You asked, "Can a character use a dagger to cut a rope or only poke holes in it?"
Since the PHB defines the damage done with a dagger as piercing, that is an argument that daggers can't do slashing damage.
The same section of the DMG says:
[Emphasis added]
So while you could argue that daggers only do piercing damage, you could also reasonably note that common definitions of daggers note they have edges.
Wikipedia says:
To me that the DMG says things in this section like "use common sense", "use your best judgment", it is entirely reasonable to note that daggers have edges, therefore they can cut ropes.
Furthermore it is reasonable and entirely supported by the DMG to note that a maul isn't going to do much (direct) damage to a rope, while a sword has a pointy tip and can reasonably poke a hole in something, at least with some effort.