The most prominent proponent of the view that fire damage/effects can't set combustible materials alight was [MENTION=2067]I'm A Banana[/MENTION]. I don't know if he still takes that view.
Starting with this, because I'm an egoist.
That's not a great understanding of my view. More precisely, I
had 4e play experience where fire damage did not set combustible materials alight. The DM's ruling was supported was supported with 4e power-card terminology that specified that the power in question targeted creatures, and thus didn't affect things that weren't creatures (similar to the Chris Perkins drow
darkfire logic), if I'm remembering correctly - the power described the rules effect, and there was nothing about setting things on fire in the power, thus there could be no setting things on fire as the result of the power. My issue at the time was less about the ruling (okay, powers have effects as described and nothing beyond them, and you don't want me to burn down a forest, both are pretty reasonable) and more about the design of a system that, in striving for clarity, actually created fictional nonsense like "this fire only burns
people" unless the DM wanted to go beyond the system's design. The DM's ruling felt consistent with the broad 4e design philosophy of "powers are for combat" (not that this was a monolithic philosophy, merely a tendency I observed in the e).
I'm sure puhlenty of DMs were house ruling on the fly to go beyond 4e's design, like, all the time, but it was at the time (and largely remains, IMO) one of my many gripes about my second favorite D&D system to date - overly precise rules effects that had the effect of severely curtailing the creative (especially out-of-combat) possibilities of the abilities of a 4e PC outside of a DM's own individual creativity. One of the not-insignificant times that 4e exhibited its occasional "good in the white room, iffy in actual play" design.
I started the thread because - as [MENTION=6801328]Elfcrusher[/MENTION] has already posted - in another thread there were some posters saying that it is a house rule to allow that fire damage (from torches, or spells, or burning oil, or whatever) might set combustible material alight.
To me that seemed less like a house rule and more like an application of the existing rules.
I think in 5e, the philosophy has clearly shifted.
If you looks at the famous guidelines for Page 42 from the 4e DMG, you see that a 7th level rogue pushing an ogre into a burning brazier might deal 2d8+5 damage with a Strength attack vs. Fortitude, because that's appropriate damage for a character of that level (you're not "giving too much away").
Meanwhile, in 5e, the rules for improvising damage suggest that stumbling into a fire pit deals 2d10 damage, and the rules for shoving a creature suggest it takes the place of one of your attacks and is done with an Athletics check vs. an Athletics or Acrobatics check, because that's just a way in which these fictional things can be modeled.
These situations look very similar, and in practice, with a confident DM, they probably flow about the same -- good DM's don't let system assumptions get in the way. But the 4e example is concerned with the metagame outcomes - What's the intent? What's the level? How effective do I want this to be? Meanwhile, the 5e version is interested in the shared fiction - what is this thing? how bad would being pushed into one be?
By way of an awkward analogy, 5e treats the burning brazier primarily as a toy. Push something into it and see what happens. Play with it. Discover what it does. Its effects are
intrinsic to it. 4e treats the burning brazier as a means to an end. It's there to deal damage, the relevant questions are how and how much. It's effects are
extrinsic to it - they depend on what you're trying to do with it in the metagame, what effects you want it to have.
In 4e, I'd probably avoid having a party that even
used torches (everywhere is basically well lit and there are sunrods and the light spell), because the metagame purpose a torch serves is largely to be able to see an enemy that, for the sake of an enjoyable combat encounter, I want the party to see anyway (unless I don't in which case torches won't help you). Hand-juggling was already a concern anyway. If I had someone who used torches for some reason, I wouldn't let them catch stuff on fire in general, doing something handwavey and indicating to the player that their "burn stuff" play agenda wasn't really something I was interested in pursuing, though I might set some terrain element that can be triggered with fire damage in a future encounter ("you can burn stuff in this controlled way"). I would probably allow them to set other torches on fire - doesn't affect the metagame consideration at all.
In 5e, its the DM's say whether something automatically succeeds, requires a roll, or automatically fails, and in most circumstances, I think I'd have a torch setting something on fire automatically succeed. I'd improvise maybe 1d10 for damage ("hot coals", sure) in combat. If they wanted to burn down a village or a forest...maybe require a roll (Survival to set it in the right place, maybe a group roll, probably of middling difficulty).
THAT would certainly change the narrative!
My change in approach largely comes from working with or against the agenda of the system. 4e asks me what about the metagame, so I think about story agendas and narrative control and I'm like "naaaah." 5e asks me what would happen, so I think about what the spread rate might be and what I might roll to ad hoc the actions of hundreds of people and I'm like "Hmm...." For me, the distinction is that 4e serves the narrative agenda I give it. 5e suggests that the important story is the story my friends an I tell ourselves about that one time we burned down the village where the villain lived. It's a lousy crafted narrative, but it's a more compelling story because it's a fun wackiness I shared with my friends. I have ownership over that experience, authorship over it, and I was perhaps surprised and delighted by the outcome. I might buzzword it by saying one is more an engine for
telling narratives, the other is more an engine for
creating experiences.
Of course, because I'm a big nerd, this probably inflates the difference, but the difference feels significant to me.