Should DnD combinations commute?

[Tehnar]

Should there be a rule in DnD (or maybe other systems as well) that for things to work (be valid by the rules), they have to commute?

By this I mean that a combination is only valid if when applied in any order is also valid.

A example being persist + extend spell. If you first apply extend and then persist, you get a 24 h duration spell. If you apply them in a different order, a spell has a duration of 48 hours. This combination does not "commute", so it would not be valid.

Would there be a benefit to this sort of a general rule?

[Foryn Gilnith]

It would cut down on complexity, in some cases. It's a personal guideline I use, and it hasn't exactly hurt me.

[Viletta Vadim]

I can't think of a case off the top of my head where it would necessarily be an unreasonable ruling. It certainly helps set a solid groundwork of precedent in your group.

[DragoonWraith]

There are far too many situations where this would come up, and to have a rule where "if order matters, you can't do it at all" is just a bad idea. Note: leveling up depends on what order you do things in (and there is a prescribed order for it).

[JeminiZero]

I would say no. There are various instances where something might be necessary, without being commutative. Class levels are one very obvious example. E.g. at level 1, you get 4x skill points and max HP. So even with the same race and stats, a 1 fighter / 1 rogue will be very different from a 1 rogue / 1 fighter.

Another example are feats. There is a good reason why you are allowed to apply feats in whichever order is most advantageous to you, rather than in whichever order you happened to take them (or something else). Lets say you are a precocious apprentice (one level 2 spell earlier than usual). And you also happen to have a sudden metamagic. You must apply precocious apprentice feat to cast the spell first, and then you can apply the sudden metamagic to modify it. The other way round simply does not work.

All these are fundamental aspects of D&D. And since they are not commutative, I would say commutativeness is not a requirement for any combination to work.

Edit, come to think of it, even equipment is not commutative. Lets say you have a heavy sword, a weak man, and a belt of strength. Assuming the sword is too heavy for the man to pick up on his own, he must wear the belt of strength first, and then pick up the sword. Other way around doesn't work. And this is in fact a rather common occurence in computer games.

[Tehnar]

Its meant more as a general rule, a specific circumstance will trump it. It is more in the line of, when in doubt, use this to fall back on to.

[dspeyer]

When I saw your question I thought of half-troll dragons and half-dragon trolls. They're very different.

It wouldn't work to ban them, though, because you never know when a base creature you want has a half- template for it somewhere.

[Runestar]

Not really. The thing is that you should be able to dictate the order in which they apply to get the more beneficial effect. For instance, the FAQ mentions twin+maximize stack because of this.

[Tokiko Mima]

Doing this would void the standing ruling of applying Maximize and Empower to the same spell and make these metamagic more powerful together.

Currently, you maximize the damage then add 50% of the base damage to the result. This results in lower overal damage than if it was applied in other ways. e.g. 10d6 Maximized + Empowered fireball does 60 + .5 * (~35) or 77.5 damage.

If it had to commute, then the you would need to apply the +50% at either time, but they would be equal. 10d6 Fireball becomes 60 Maximized and 90 Empowered, or in reverse, 10d6 becomes 15d6 Empowered, and 90 when Maximized.

It effectively doubles the power of Empower without increasing the metamagic slot cost.

[Tehnar]

Currently for empower and maximize specifically support commutativity, as it doesn't matter in what order you apply them. Empower adds +50% of dice, and maximize applies only to the base. So a fireball is 60+5d6 or 5d6 + 60. Ie each effect is applied independently and then added together.

It doesn't matter which order they were applied to.

[Prime32]

When I saw your question I thought of half-troll dragons and half-dragon trolls. They're very different.

It wouldn't work to ban them, though, because you never know when a base creature you want has a half- template for it somewhere.

Besides, that's how real-life hybrids work. Compare a mule with a hinny.

It gets worse in the above case, since if the mother is a troll they will presumably give birth, but if the mother is a dragon the hybrid will hatch from an egg.

[hamishspence]

When I saw your question I thought of half-troll dragons and half-dragon trolls. They're very different.

Might be rather interesting to see a troll-dragon villain pairing, with their children being a mix of both- warty green dragons, and winged, scaly trolls.

I wonder how many "odd pairs" one could do?

Half-dragon fiend + half-fiend dragon
Half dragon celestial + half celestial dragon

Half-dragon fey + half-fey dragon

And with Savage Species, though I'm not sure if its supposed to be interpreted this way:

Gelatinous dragon + half-dragon gelatinous cube.

[Optimystik]

Might be rather interesting to see a troll-dragon villain pairing, with their children being a mix of both- warty green dragons, and winged, scaly trolls.

If by "interesting" you mean "disgusting," then yes.

[hamishspence]

Shrek had a Dragon-Donkey pairing- and the offspring look a bit different from each other.

D&D seems to have a lot of templates that can produce different results if you pick one combination of two creatures, than if you pick another combination.

(There is also the fact that Skeletal Dragons are different from Dragon Skeletons, and Zombie Dragons are different from Dragon Zombies- but thats more a case of Draconomicon introducing new templates. It also has a black dragon villain very keen on creating hybrids as followers- including Half-dragon shambling mounds.)