Can you move through an object's space according to RAW?

Question

This looks like a trivial question, but I didn't find a sound answer in the rules.

The rules explicitly allows you to move through a nonhostile creature's space:

You can move through a nonhostile creature's space.
(Basic Rules, "Moving Around Other Creatures")

The rules also allow you to move through a creature two sizes larger or smaller:

you can move through a hostile creature's space only if the creature is at least two sizes larger or smaller than you

Whether a creature is a friend or an enemy, you can't willingly end your move in its space. But what about objects? They have the same size categories as creatures do. Does an object's size category directly affect what area this object can block?

Can you move through a Large wooden box's space? Can you willingly end your move in a Medium cauldron's space?

Inspired by this question and its comments, which apparently assumes an object Size category works the same way as a creature Size:

If the answer is "it doesn't occupy any space," then it doesn't have a meaningful size on the grid.

Size is also a defined game term.

I think it's clear to anyone that plays the game.

Answer 1

Maybe

You had stated that you couldn't find a sound answer in the rules to the question of whether you could move through an object's space and to the best of my knowledge as someone that's read the DMG cover to cover, there isn't one to that specific issue because there can't be one that would cover absolutely everything.

Can you move through the space of a Large wooden box? Maybe yes if the box is empty and has holes of adequate size; maybe no if the box is full of watermelons; maybe yes if the box is solid but you can make a strength check to Kool-Aid man through the wall. They're all large boxes, but the manner by which they're handled for the sake of moving through their space depends on the circumstances. Hence the general catchall of rulings, not rules which is helpful for adjudicating the endless situations one can come up with for characters interacting with objects.

Generally speaking, the rules of 5e aren't suitable for providing concrete direction on every type of interaction a character can have with an object. To quote the initial Sage Advice column:

The DM is key. Many unexpected things can happen in a D&D campaign, and no set of rules could reasonably account for every contingency. If the rules tried to do so, the game would become unplayable. An alternative would be for the rules to severely limit what characters can do, which would be counter to the open-endedness of D&D. The direction we chose for the current edition was to lay a foundation of rules that a DM could build on, and we embraced the DM’s role as the bridge between the things the rules address and the things they don’t.

To that end, the DM will have to make a call.

Answer 2

Objects and creatures take up space differently.

You can't apply anything about moving through a creature's space to moving past objects. Creatures occupy their space. As such, a gnome and a goliath occupy the same space. This is clearly different from how a a gnome-sized mannequin and a goliath-size mannequen would affect movement in a 5 x 5 foot space.

Occupying Space is a game mechanic to control movement, primarily in combat. Objects are just things in the way.

So, it's up to the DM to decide.

I would recommend some type of scale where:

1. Objects start to create difficult terrain at some point, but that penalty can be overcome by an athletics or acrobatics check.
2. Object are difficult terrain without the ability to overcome the penalty. This would encompass squeezing rules.
3. Objects block the way and characters must use climb, jump, break them down, etc. to get past them.

Oh, and don't forget the Rule of Cool when dealing with movement around obstacles. This is a good chance for players to be creative about how they overcome the obstacles.

Answer 3

Moving through object: it depends.

I (mis-used) related rules for a chase through a busy marketplace based on overland travel/difficult terrain - halving movement speed for passing through obstacles (aka heavy terrain):

1. My players saw a pickpocket-spiel in a marketplace - the thiefs did the ususal 3 on 1: 1 runs into the mark and is apolegetic about it, helping it back up and patting them down, etc. Another pickpockets the mark while it is beign fussed over by the first and passes the object to a third which casually walks away.

2. Normally the marketplace is a big open place with a few fixed stalls (smithy, butcher, ...) for everyday-sales. On market day though plenty of smaller tents, carts & carriages as well as arrangements of baskets/boxes with goods in them are stuffed between the fixed stalls - only small alleys are left.

3. Players were warned about pickpockets, keeping track of their surroundings while equipping for a travel ahead. They picked up on what some thiefs did, detected the object-pass and two of them gave chase while the others tried to "arrest" the bumper and the actual pickpocket which quickly escalated into a brawl.

I opted to ignore other shoppers (thiefs and players needed to pass by them) and borrrowed/simplified from special movement:

Staying in the alleys was normal movement, passing through occupied spaces (basket/boxes, carts/carriages, tents) took 100% movement penalty (5->10).

The fleeing thief mostly used alleys and the fixed stalls/tents to try to break sight and get lost.

However, the players started moving through occupied fields and had options to avoid the doubling of movement costs:

• baskets/boxes could be passed through or vaulted over (Acrobatics/Dex: passing through, Athletics/Str: jump)
• carts/carriages could only be vaulted (Athletics/Str: jump)

Missing a dex check just meant it cost the original 10 movement to pass, missing a jump cost another 5 movement on top (15 instead of 10) to get back up.

It was quite a bit of dice rolling (due to the time constraints) - eventually they caught up and arrested the thief.

For a non-time constraint situation I would simply double the movement costs and be done with it.

Similar movement impeding effects (terrain wise) are applied through spells, namely:

• Spike growth (2nd) - difficult terrain + damage
• Plant growth (3rd) - quadrupling movement costs

which could also give you some help about how to rule it.