Yeah I totally agree, and I think that I figured out the explanation for denying this idea, particularly with grid-based play. A creature occupies a 5-foot cube of space. Even when the wall cuts through at only 1 inch high, it's still cutting through that cube. A creature is not pushed within its own cube, it's pushed one cube over, similar to if it was shoved with the shove action. So, if you are attempting to push a creature downwards, you would have to be able to push it into the next cube, which in this case is occupied by solid earth. Since the creature cannot occupy that space, it simply cannot be pushed in that direction (in my opinion anyway). If it's possible to push the creature the other way (upwards) then it goes that way instead. In this case, it would be pushed 5 feet into the air and then it would fall 4 feet 11 inches (give or take a quarter of an inch) back onto the surface of the wall.
In fact, because the description of the Wall says that "It can be free floating or resting on a solid surface" combined with this business of pushing creatures aside, I would rule that the Wall cannot be constructed in a manner that cuts through any solid object at all. As a consequence, I would rule that in some cases a creature could actually be in the way of constructing the wall in the first place -- for example, if the creature is standing in a tunnel with a 5 foot ceiling I would rule that you cannot construct this horizontal wall at all because the creature cannot be pushed into the next cube in either direction.
Sight aside, unless a spell says otherwise, you cannot target a creature behind total cover with a spell.
If you rule that Wall of Force provides total cover, then you cannot cast counterspell on someone on the opposite side of one. If you don’t rule that Wall of Force provides total cover, then you can, but that will likely lead to some other degenerate interactions.
I prefer "DM decisions" to "degenerate interactions" :) ... but your point stands.
1) If WoF is total cover then no spells can be targeted at something on the other side of it since the Line of Effect is blocked.
2) If WoF is not total cover then creatures on the other side of it CAN be targeted by a spell (assuming that the spell only requires seeing the target). However, the DM then has to decide on a case by case basis, usually based on the specific text of the spell, whether it can be blocked by a wall of force.
As an example, fireball says that a spark streaks from your finger to the point that is targeted. In addition, the example on line of effect specifically has a fireball being blocked by a wall (since fireball doesn't actually require seeing the point it is targeted at). So, in this case, fireball would pretty clearly be blocked by a WoF. However, chill touch manifests a spectral hand beside the target that inflicts the damage. There is no text implying a physical component that needs to travel from the caster to the target, that would be stopped by a wall that prevents something from physically passing through it.
Both of these rulings can be justified as RAW depending on how the DM decides to interpret the rules. The first is easier to implement but also makes Wall of Force much more powerful in certain scenarios. The latter requires a DM to make a lot of rulings considering how each spell would interact with WoF on a case by case basis. WoF remain a powerful spell, but it won't completely shut down opposing spellcasters.
Wall of force is invisible, therefore you can see the target, you can hear them too. That is more then you need to counter. The spell is not "Passing through" anything to counter.. it has no "travel path". the spell is not PHYSICAL either..
You can see them but you can't hear them. Wall of Force prevents anything from physically passing through it and sound is vibrations in the air which would be prevented from passing through. Wall of Force is like an invisible solid wall - sound does not pass through it. However, the rest of your comments are correct if the DM decides that a Wall of Force does not provide total cover.
P.S. Air is something physical and can not pass through a Wall of Force
Note that these are unofficial opinions from developers describing how they might choose to run it. None of these made it into the Sage Advice Compendium which is considered official clarifications (as much as anything is official).
Interesting, though I still say this seems to clash with how in one instance we have a spell that is very clear that it blocks magic from passing through it, and another spell that lacks that language.
Yea the rules for transparent cover are quite a mess. It is very clear that the intention of the designers is that a physical barrier is meant to stop line of effect for spells. And that goes for both a opaque barrier such as a wall or door and for transparent barriers such as windows or (spell) force effects. Spells with range (self) and a visual requirement, such as Misty Step, still work as usual though.
This is something I really wish they clear up in the new edition.
Part of the problem though is that they total cover rules apply to all targeted effects including attacks. Treating a thin pane of glass (or even cellophane) as total cover means you can't target anything on the other side of it - neither spells nor heavy crossbow bolts.
Can you cast a spell through a thin window? Not if it is total cover and because it is magic, no one really knows what could stop a spell and what couldn't. However, that thin window would prove little or no hindrance to a heavy crossbow bolt capable of punching through plate armor. But by the same targeting rules of total cover, you can't even target the crossbow bolt at a target you can see on the other side of a window, which I find to not make sense.
When the devs say a window provides total cover, I mostly stop listening to them because they appear to not have thought it through sufficiently. I find that sage advice comments like these come from a desire to not change the text of the rules to clarify what they should mean. Another great example is JC saying that a creature with the See Invisible spell on them still has disadvantage to hit a creature with the Invisible condition because the spell doesn't say anything about countering the condition - it only lets you see the invisible creature (which to me should cancel the condition on a case by case basis but the "design" intent seems to be that if a creature has a condition applied to them then other effects can't conditionally remove it for some creatures and not others - which is a design failure that doesn't replicate common experience.
Total cover, invisibility, vision rules for natural and magical darkness lumped together with heavily obscured from a number of other effects (like foliage ...). Trying to "simplify" the rules runs into logical inconsistencies when you try to include too many different things in one rule. The solution is not to double down on the inconsistencies but re-design the rules to better describe player expectations - I am hoping the next edition fixes some of these issues too.
A source of cover is àn obstacle that makes a target more difficult to harm, a window can certainly fit that description but its up to the DM to determine the degree of cover of any obstacle The lead rule developper provided an opinion on the matter possibly alluding at how its intended but in the end everyone can rule how they want in the absence of official ruling on the matter.
You can see them but you can't hear them. Wall of Force prevents anything from physically passing through it and sound is vibrations in the air which would be prevented from passing through. Wall of Force is like an invisible solid wall - sound does not pass through it. However, the rest of your comments are correct if the DM decides that a Wall of Force does not provide total cover.
P.S. Air is something physical and can not pass through a Wall of Force
The thing is, we know from real life experience that sound does pass through solid walls. For completeness, let's remember that the wall created by this spell might not be enclosed, it might just be a wall, and obviously sound can travel "around" a wall quite easily. But as for an enclosed Wall of Force, I think that it's reasonable to allow sound to travel through it. Sound waves do not travel through walls via any sort of physical air particles travelling through it -- there is another scientific explanation that could be googled but is beyond the scope here. Likewise, radiation, radio waves, cell phone signals and other non-physical entities could pass through a Wall of Force if such things existed. But sound is the most relevant since there is a whole category of damage, thunder damage, that might apply from spells such as Thunderwave. Of course, in real life usually not all sound makes it through solid walls -- it's dampened pretty significantly. Should a DM take this into account somehow? Perhaps a creature gains advantage on their saving throw vs Thunderwave? This level of granularity is just up to the DM to make a situational ruling.
Part of the problem though is that they total cover rules apply to all targeted effects including attacks. Treating a thin pane of glass (or even cellophane) as total cover means you can't target anything on the other side of it - neither spells nor heavy crossbow bolts.
Can you cast a spell through a thin window? Not if it is total cover and because it is magic, no one really knows what could stop a spell and what couldn't. However, that thin window would prove little or no hindrance to a heavy crossbow bolt capable of punching through plate armor. But by the same targeting rules of total cover, you can't even target the crossbow bolt at a target you can see on the other side of a window, which I find to not make sense.
When the devs say a window provides total cover, I mostly stop listening to them . . .
In my opinion, I think that it's reasonable for a DM to treat a thin layer of glass such as a window in a similar manner to thin foliage. Depending on the nature of the foliage in question I think that a DM could declare that it provides only half cover or three-quarters cover or even no cover at all even if a creature is located completely behind it. The short section which describes the rules for cover use the word "obstacle" six times. It also uses the phrases "making a target more difficult to harm" and "the most protective degree of cover". The implication is that the obstacle must be sturdy enough to hinder (for certain types of partial cover like thin foliage) or completely block standard ranged attacks such as from bolts and arrows. A creature is only behind total cover when completely concealed by such an obstacle (that is sufficiently sturdy).
A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.
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"Sooner or later, your Players are going to smash your railroad into a sandbox."
-Vedexent
"real life is a super high CR."
-OboeLauren
"............anybody got any potatoes? We could drop a potato in each hole an' see which ones get viciously mauled by horrible monsters?"
The degree of cover is the ammount of your body being covered by an obstacle, half of it, three-quarter or total, regardless of its hardness. So it starts by determining if something is enought of an obstacle to grant cover and if so, to which degree.
The degree of cover is the ammount of your body being covered by an obstacle, half of it, three-quarter or total, regardless of its hardness. So it starts by determining if something is enought of an obstacle to grant cover and if so, to which degree.
In my opinion, this view of what qualifies for various degrees of cover is too restrictive and is not the intended interpretation.
The way I read the section on cover is that the main idea for the concept is described first and then some examples are given of situations that qualify for various degrees of cover. But this doesn't mean that there aren't also other situations which also qualify. The main concept is that "obstacles can provide cover during combat, making a target more difficult to harm", and that "there are three [protective] degrees of cover". In other words, three levels of protection (+2 AC, +5 AC, and untargetable). The chosen examples for partial cover which follow all do emphasize that only a portion of a creature's body needs to be behind cover to qualify as receiving partial cover. In my opinion these examples are mentioned to make sure that players understand that these cases do qualify (as opposed to not qualifying at all). They aren't trying to create a restriction that these are the only cases which qualify.
The example given for total cover is that "A target has total cover if it is completely concealed by an obstacle". As previously discussed, the developers have already clarified that the use of the word "concealed" in this context does not refer to whether or not the target can be seen -- instead it's referring back to the overall concept (making a target more difficult to harm / levels of protection). In other words, the intention was for "concealed" to be interpreted something like: "A target has total cover if it is completely [behind] an obstacle [that provides enough protection] (such that it can't be targeted directly by an attack or a spell)".
If the degrees of cover were ONLY determined by the amount of your body being covered regardless of its hardness (as you've said in your post) then if a creature is completely behind something the only choices for a DM would be to provide no cover or total cover. But there are tons of common sense scenarios where this would make no sense, many of which have already been mentioned in this thread such as thin foliage, a thick curtain or a pane of glass. These should all quite obviously be granted a bonus to AC while still allowing for the possibility of targeting and potentially hitting the creature behind such obstacles. To rule otherwise would be to ignore the overall concept defined in the section on cover which is simply that it makes a target more difficult to harm in three varying degrees.
Under your interpretation it should be impossible for a creature to hide behind partial cover. In order to Hide you must be Unseen, so if partial cover can only be achieved when only partially behind the obstacle then you could never also be Unseen.
Lost Mine of Phandelver is an official 5e adventure which was packaged with a Starter Set and was designed to introduce new players to many of the basic rules of the game. There are at least two examples in this adventure where a creature is able to Hide but the obstacle is explicitly declared to provide only half cover by the adventure text:
(Mild Spoilers)
At the entrance to the Goblin Hideout there is an area described as "dense briar thickets" which are "impenetrable from the west side of the stream". The goblins within these thickets cannot be seen until "the characters cross to the east side of the stream [and] they can see around the screening thickets". If the characters remain on the initial side of the thicket and make a lot of noise the goblins have the capability to "attack them through the thicket, which provides the goblins with half cover". In a block of text designed to be read out loud to describe the area within the thickets, it's revealed that "Wooden planks flatten out the briars and provide room for guards to lie hidden and watch the area". The adventure then again reiterates the possibility for the prior conflict with "If the goblins notice intruders in area 1, they open fire with their bows, shooting through the thickets and probably catching the characters by surprise. As we know from the rules for surprise -- surprise is only possible when someone is successfully Hidden. Lastly, this section again further describes these thickets: "Thickets. The thickets around the clearing are difficult terrain, but they aren’t dangerous—just annoying. They provide half cover to creatures behind them."
The second place that this occurs in this adventure is also in the Goblin Hideout. The read out-loud text describes that "Sacks and crates of looted provisions are piled up in the south end of this large cave." The adventure text explicitly states that "The piles of sacks and crates can provide half cover to any creature fighting or hiding behind them." In addition, "the goblins take cover behind the piles of supplies, hoping to ambush the characters." Despite being positioned behind an obstacle that provides only half cover, they are potentially capable of creating an ambush from there -- meaning that they can attempt to Hide and then Surprise the PCs from there.
This adventure is clearly using an interpretation for the rules of cover which align with what I'm describing.
In my opinion, the DM should rule that there is a degree of cover provided by an obstacle that makes the most sense for the situation depending on to what degree that obstacle is "making a target more difficult to harm".
In my opinion, this view of what qualifies for various degrees of cover is too restrictive and is not the intended interpretation.
We can't really know intentions but RAW it's clear to me the degree of cover is based on how much proportion of the body is covered as that's how its being referenced.
Any specific ruling in adventure may vary from general rules, Lost Mine of Phandelver is an exemple of that, it uses thicket that is impenetrable, but is difficult terrain and half cover otherwise, allowing goblins to hide despite not being lightly or heavily obscured area per se, meaning the foliage still prevent them from being seen clearly somehow.
Half Cover: A target has half cover if an obstacle blocks at least half of its body.
Three-Quarters Cover: A target has three-quarters cover if about three-quarters of it is covered by an obstacle.
Total Cover: A target has total cover if it is completely concealed by an obstacle.
Hiding: You can't hide from a creature that can see you clearly
Can you cast a spell through a thin window? Not if it is total cover and because it is magic, no one really knows what could stop a spell and what couldn't. However, that thin window would prove little or no hindrance to a heavy crossbow bolt capable of punching through plate armor. But by the same targeting rules of total cover, you can't even target the crossbow bolt at a target you can see on the other side of a window, which I find to not make sense.
I would note that the problem isn't limited to transparent cover; a large sheet of paper is also an obstacle even if it won't stop any serious attack.
A particular ski resort categorizes their trails into trails suitable for beginners, trails suitable for intermediate skiers, and trails suitable for experts. Every trail has a name. For example, the easiest trail is called the "Bunny Slope". In the guidebook for the ski resort there is a section with the heading "Trail Difficulty". It says, "ski slopes are designed to provide a challenge during a skier's descent, making the slope more difficult to ski -- there are three degrees of difficulty." Next, it explains "A trail is suitable for beginners if it is marked with a green sign. A trail is suitable for intermediates if it is marked with a blue sign. A trail is suitable for experts if it is marked with a black sign." That's all the guidebook says on the subject.
Does this mean that a trail is only suitable for beginners if it's marked with a green sign? No. The Bunny Trail is the site of ski lessons and first-time and inexperienced skiers. It turns out that the Bunny Trail is so easy and so short that it is not marked with a color. It is labelled with a plain white sign that says "Bunny Trail". So, at this resort, despite the lack of completeness of the guidebook, any trail marked with a green sign qualifies as a trail suitable for beginners AND any trail that is named and labelled "Bunny Trail" also qualifies as a trail suitable for beginners. There may be additional trails which qualify as well.
Is the fact that some trails are marked with a green sign the important concept to keep in mind? No. The whole purpose of the categorization of the ski slopes is so that people understand that some slopes exist that are making the trail more difficult to ski and that there are three degrees of difficulty.
When it comes to the rules for Cover, the main concept is that "obstacles can provide cover during combat, making a target more difficult to harm", and that "there are three degrees of cover". The rules go on to confirm that if a certain percentage of the body is behind the obstacle then that situation qualifies as partial cover but it does not say that that is the only situation that qualifies. It simply doesn't give any additional examples.
By using this interpretation we can allow the DM to decide on the degree of cover based on the entire situation. The DM should be able to draw inspiration from officially published examples (like in Lost Mine of Phandelver) for how to apply the rules. This solves many of the "problems" discussed in this thread such as the pane of glass, the thin foliage or the sheet of paper and IMO it's a valid interpretation of the RAW.
To put it simple, the DM determine if something is enought of an obstacle to grant cover and if so, to what ammount between 50%, 75% or 100% of the body.
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Yeah I totally agree, and I think that I figured out the explanation for denying this idea, particularly with grid-based play. A creature occupies a 5-foot cube of space. Even when the wall cuts through at only 1 inch high, it's still cutting through that cube. A creature is not pushed within its own cube, it's pushed one cube over, similar to if it was shoved with the shove action. So, if you are attempting to push a creature downwards, you would have to be able to push it into the next cube, which in this case is occupied by solid earth. Since the creature cannot occupy that space, it simply cannot be pushed in that direction (in my opinion anyway). If it's possible to push the creature the other way (upwards) then it goes that way instead. In this case, it would be pushed 5 feet into the air and then it would fall 4 feet 11 inches (give or take a quarter of an inch) back onto the surface of the wall.
In fact, because the description of the Wall says that "It can be free floating or resting on a solid surface" combined with this business of pushing creatures aside, I would rule that the Wall cannot be constructed in a manner that cuts through any solid object at all. As a consequence, I would rule that in some cases a creature could actually be in the way of constructing the wall in the first place -- for example, if the creature is standing in a tunnel with a 5 foot ceiling I would rule that you cannot construct this horizontal wall at all because the creature cannot be pushed into the next cube in either direction.
I prefer "DM decisions" to "degenerate interactions" :) ... but your point stands.
1) If WoF is total cover then no spells can be targeted at something on the other side of it since the Line of Effect is blocked.
2) If WoF is not total cover then creatures on the other side of it CAN be targeted by a spell (assuming that the spell only requires seeing the target). However, the DM then has to decide on a case by case basis, usually based on the specific text of the spell, whether it can be blocked by a wall of force.
As an example, fireball says that a spark streaks from your finger to the point that is targeted. In addition, the example on line of effect specifically has a fireball being blocked by a wall (since fireball doesn't actually require seeing the point it is targeted at). So, in this case, fireball would pretty clearly be blocked by a WoF. However, chill touch manifests a spectral hand beside the target that inflicts the damage. There is no text implying a physical component that needs to travel from the caster to the target, that would be stopped by a wall that prevents something from physically passing through it.
Both of these rulings can be justified as RAW depending on how the DM decides to interpret the rules. The first is easier to implement but also makes Wall of Force much more powerful in certain scenarios. The latter requires a DM to make a lot of rulings considering how each spell would interact with WoF on a case by case basis. WoF remain a powerful spell, but it won't completely shut down opposing spellcasters.
You can see them but you can't hear them. Wall of Force prevents anything from physically passing through it and sound is vibrations in the air which would be prevented from passing through. Wall of Force is like an invisible solid wall - sound does not pass through it. However, the rest of your comments are correct if the DM decides that a Wall of Force does not provide total cover.
P.S. Air is something physical and can not pass through a Wall of Force
Note that these are unofficial opinions from developers describing how they might choose to run it. None of these made it into the Sage Advice Compendium which is considered official clarifications (as much as anything is official).
Part of the problem though is that they total cover rules apply to all targeted effects including attacks. Treating a thin pane of glass (or even cellophane) as total cover means you can't target anything on the other side of it - neither spells nor heavy crossbow bolts.
Can you cast a spell through a thin window? Not if it is total cover and because it is magic, no one really knows what could stop a spell and what couldn't. However, that thin window would prove little or no hindrance to a heavy crossbow bolt capable of punching through plate armor. But by the same targeting rules of total cover, you can't even target the crossbow bolt at a target you can see on the other side of a window, which I find to not make sense.
When the devs say a window provides total cover, I mostly stop listening to them because they appear to not have thought it through sufficiently. I find that sage advice comments like these come from a desire to not change the text of the rules to clarify what they should mean. Another great example is JC saying that a creature with the See Invisible spell on them still has disadvantage to hit a creature with the Invisible condition because the spell doesn't say anything about countering the condition - it only lets you see the invisible creature (which to me should cancel the condition on a case by case basis but the "design" intent seems to be that if a creature has a condition applied to them then other effects can't conditionally remove it for some creatures and not others - which is a design failure that doesn't replicate common experience.
Total cover, invisibility, vision rules for natural and magical darkness lumped together with heavily obscured from a number of other effects (like foliage ...). Trying to "simplify" the rules runs into logical inconsistencies when you try to include too many different things in one rule. The solution is not to double down on the inconsistencies but re-design the rules to better describe player expectations - I am hoping the next edition fixes some of these issues too.
A source of cover is àn obstacle that makes a target more difficult to harm, a window can certainly fit that description but its up to the DM to determine the degree of cover of any obstacle The lead rule developper provided an opinion on the matter possibly alluding at how its intended but in the end everyone can rule how they want in the absence of official ruling on the matter.
The thing is, we know from real life experience that sound does pass through solid walls. For completeness, let's remember that the wall created by this spell might not be enclosed, it might just be a wall, and obviously sound can travel "around" a wall quite easily. But as for an enclosed Wall of Force, I think that it's reasonable to allow sound to travel through it. Sound waves do not travel through walls via any sort of physical air particles travelling through it -- there is another scientific explanation that could be googled but is beyond the scope here. Likewise, radiation, radio waves, cell phone signals and other non-physical entities could pass through a Wall of Force if such things existed. But sound is the most relevant since there is a whole category of damage, thunder damage, that might apply from spells such as Thunderwave. Of course, in real life usually not all sound makes it through solid walls -- it's dampened pretty significantly. Should a DM take this into account somehow? Perhaps a creature gains advantage on their saving throw vs Thunderwave? This level of granularity is just up to the DM to make a situational ruling.
In my opinion, I think that it's reasonable for a DM to treat a thin layer of glass such as a window in a similar manner to thin foliage. Depending on the nature of the foliage in question I think that a DM could declare that it provides only half cover or three-quarters cover or even no cover at all even if a creature is located completely behind it. The short section which describes the rules for cover use the word "obstacle" six times. It also uses the phrases "making a target more difficult to harm" and "the most protective degree of cover". The implication is that the obstacle must be sturdy enough to hinder (for certain types of partial cover like thin foliage) or completely block standard ranged attacks such as from bolts and arrows. A creature is only behind total cover when completely concealed by such an obstacle (that is sufficiently sturdy).
"Sooner or later, your Players are going to smash your railroad into a sandbox."
-Vedexent
"real life is a super high CR."
-OboeLauren
"............anybody got any potatoes? We could drop a potato in each hole an' see which ones get viciously mauled by horrible monsters?"
-Ilyara Thundertale
The degree of cover is the ammount of your body being covered by an obstacle, half of it, three-quarter or total, regardless of its hardness. So it starts by determining if something is enought of an obstacle to grant cover and if so, to which degree.
In my opinion, this view of what qualifies for various degrees of cover is too restrictive and is not the intended interpretation.
The way I read the section on cover is that the main idea for the concept is described first and then some examples are given of situations that qualify for various degrees of cover. But this doesn't mean that there aren't also other situations which also qualify. The main concept is that "obstacles can provide cover during combat, making a target more difficult to harm", and that "there are three [protective] degrees of cover". In other words, three levels of protection (+2 AC, +5 AC, and untargetable). The chosen examples for partial cover which follow all do emphasize that only a portion of a creature's body needs to be behind cover to qualify as receiving partial cover. In my opinion these examples are mentioned to make sure that players understand that these cases do qualify (as opposed to not qualifying at all). They aren't trying to create a restriction that these are the only cases which qualify.
The example given for total cover is that "A target has total cover if it is completely concealed by an obstacle". As previously discussed, the developers have already clarified that the use of the word "concealed" in this context does not refer to whether or not the target can be seen -- instead it's referring back to the overall concept (making a target more difficult to harm / levels of protection). In other words, the intention was for "concealed" to be interpreted something like: "A target has total cover if it is completely [behind] an obstacle [that provides enough protection] (such that it can't be targeted directly by an attack or a spell)".
If the degrees of cover were ONLY determined by the amount of your body being covered regardless of its hardness (as you've said in your post) then if a creature is completely behind something the only choices for a DM would be to provide no cover or total cover. But there are tons of common sense scenarios where this would make no sense, many of which have already been mentioned in this thread such as thin foliage, a thick curtain or a pane of glass. These should all quite obviously be granted a bonus to AC while still allowing for the possibility of targeting and potentially hitting the creature behind such obstacles. To rule otherwise would be to ignore the overall concept defined in the section on cover which is simply that it makes a target more difficult to harm in three varying degrees.
Under your interpretation it should be impossible for a creature to hide behind partial cover. In order to Hide you must be Unseen, so if partial cover can only be achieved when only partially behind the obstacle then you could never also be Unseen.
Lost Mine of Phandelver is an official 5e adventure which was packaged with a Starter Set and was designed to introduce new players to many of the basic rules of the game. There are at least two examples in this adventure where a creature is able to Hide but the obstacle is explicitly declared to provide only half cover by the adventure text:
(Mild Spoilers)
At the entrance to the Goblin Hideout there is an area described as "dense briar thickets" which are "impenetrable from the west side of the stream". The goblins within these thickets cannot be seen until "the characters cross to the east side of the stream [and] they can see around the screening thickets". If the characters remain on the initial side of the thicket and make a lot of noise the goblins have the capability to "attack them through the thicket, which provides the goblins with half cover". In a block of text designed to be read out loud to describe the area within the thickets, it's revealed that "Wooden planks flatten out the briars and provide room for guards to lie hidden and watch the area". The adventure then again reiterates the possibility for the prior conflict with "If the goblins notice intruders in area 1, they open fire with their bows, shooting through the thickets and probably catching the characters by surprise. As we know from the rules for surprise -- surprise is only possible when someone is successfully Hidden. Lastly, this section again further describes these thickets: "Thickets. The thickets around the clearing are difficult terrain, but they aren’t dangerous—just annoying. They provide half cover to creatures behind them."
The second place that this occurs in this adventure is also in the Goblin Hideout. The read out-loud text describes that "Sacks and crates of looted provisions are piled up in the south end of this large cave." The adventure text explicitly states that "The piles of sacks and crates can provide half cover to any creature fighting or hiding behind them." In addition, "the goblins take cover behind the piles of supplies, hoping to ambush the characters." Despite being positioned behind an obstacle that provides only half cover, they are potentially capable of creating an ambush from there -- meaning that they can attempt to Hide and then Surprise the PCs from there.
This adventure is clearly using an interpretation for the rules of cover which align with what I'm describing.
In my opinion, the DM should rule that there is a degree of cover provided by an obstacle that makes the most sense for the situation depending on to what degree that obstacle is "making a target more difficult to harm".
We can't really know intentions but RAW it's clear to me the degree of cover is based on how much proportion of the body is covered as that's how its being referenced.
Any specific ruling in adventure may vary from general rules, Lost Mine of Phandelver is an exemple of that, it uses thicket that is impenetrable, but is difficult terrain and half cover otherwise, allowing goblins to hide despite not being lightly or heavily obscured area per se, meaning the foliage still prevent them from being seen clearly somehow.
I would note that the problem isn't limited to transparent cover; a large sheet of paper is also an obstacle even if it won't stop any serious attack.
For fun I'm going to try an analogy:
A particular ski resort categorizes their trails into trails suitable for beginners, trails suitable for intermediate skiers, and trails suitable for experts. Every trail has a name. For example, the easiest trail is called the "Bunny Slope". In the guidebook for the ski resort there is a section with the heading "Trail Difficulty". It says, "ski slopes are designed to provide a challenge during a skier's descent, making the slope more difficult to ski -- there are three degrees of difficulty." Next, it explains "A trail is suitable for beginners if it is marked with a green sign. A trail is suitable for intermediates if it is marked with a blue sign. A trail is suitable for experts if it is marked with a black sign." That's all the guidebook says on the subject.
Does this mean that a trail is only suitable for beginners if it's marked with a green sign? No. The Bunny Trail is the site of ski lessons and first-time and inexperienced skiers. It turns out that the Bunny Trail is so easy and so short that it is not marked with a color. It is labelled with a plain white sign that says "Bunny Trail". So, at this resort, despite the lack of completeness of the guidebook, any trail marked with a green sign qualifies as a trail suitable for beginners AND any trail that is named and labelled "Bunny Trail" also qualifies as a trail suitable for beginners. There may be additional trails which qualify as well.
Is the fact that some trails are marked with a green sign the important concept to keep in mind? No. The whole purpose of the categorization of the ski slopes is so that people understand that some slopes exist that are making the trail more difficult to ski and that there are three degrees of difficulty.
When it comes to the rules for Cover, the main concept is that "obstacles can provide cover during combat, making a target more difficult to harm", and that "there are three degrees of cover". The rules go on to confirm that if a certain percentage of the body is behind the obstacle then that situation qualifies as partial cover but it does not say that that is the only situation that qualifies. It simply doesn't give any additional examples.
By using this interpretation we can allow the DM to decide on the degree of cover based on the entire situation. The DM should be able to draw inspiration from officially published examples (like in Lost Mine of Phandelver) for how to apply the rules. This solves many of the "problems" discussed in this thread such as the pane of glass, the thin foliage or the sheet of paper and IMO it's a valid interpretation of the RAW.
To put it simple, the DM determine if something is enought of an obstacle to grant cover and if so, to what ammount between 50%, 75% or 100% of the body.