D&D General "that you can see", "line of sight", glass, mirrors, ~clairvoyance, blindsight, and anything else.

[greg kaye]

So here are some situations regarding a potential target of a potential effect of such a thing as a spell.
1. the target is within range but on the other side of a transparent, solid barrier such as glass.
2. the target is within range but cannot be directly seen due to an inability to turn or due to an obstruction such as a wall but you are still able to view the target due to something such as a local, perhaps handheld mirror.
2. the target is within range but cannot be directly seen due to an inability to turn or due to an obstruction such as a wall but you are still able to view the target due to something such as a large but distant mirror.
3. the target is within range and on the other side of a restriction to vision such as containment but you are still able to view the target thanks to an ability such as clairvoyance.

So let's say that an ally would benefit from the effect of healing word or you want to attack an opponent with a spell such as feeblemind or magic missile - in what situations would these spells still work? To what extent could the missiles be magical? What about nonpersonal targets such as that relating to mold earth? Anything else related to uses of "that you can see" and "line of sight" wording?

 

[Oofta]

Going by the PHB
Total Cover

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.​

Targets: A Clear Path to the Target

To target something, you must have a clear path to it, so it can’t be behind total cover.​

​

If you place an area of effect at a point that you can’t see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.​

Spellcasting: Areas of Effect

A spell’s effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn’t included in the spell’s area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.​

So here are some situations regarding a potential target of a potential effect of such a thing as a spell.
1. the target is within range but on the other side of a transparent, solid barrier such as glass.

Depending on the point of origin, even glass will block a spell. Up to the DM of course, might be more fun to have that lightning bolt shatter the window.

2. the target is within range but cannot be directly seen due to an inability to turn or due to an obstruction such as a wall but you are still able to view the target due to something such as a local, perhaps handheld mirror.

You have to have a clear path to the target. If using a mirror you don't have that.

2. the target is within range but cannot be directly seen due to an inability to turn or due to an obstruction such as a wall but you are still able to view the target due to something such as a large but distant mirror.
3. the target is within range and on the other side of a restriction to vision such as containment but you are still able to view the target thanks to an ability such as clairvoyance.

You have a clear path which means it can't be behind total cover, your target can't be behind an obstacle. Total cover does not mean you have to have to be able to see something. Many spells are creature or point you can see.

So let's say that an ally would benefit from the effect of healing word or you want to attack an opponent with a spell such as feeblemind or magic missile - in what situations would these spells still work? To what extent could the missiles be magical? What about nonpersonal targets such as that relating to mold earth? Anything else related to uses of "that you can see" and "line of sight" wording?

Spells like healing word explicitly state that you have to be able to see them. In other words, if your healer is blind they can't target anyone. You still have to have to meet the other conditions such as a clear path.

 

[Umbran]

I generally go with an unobstructed and straight line path from the eyes (or sensory organs) of the caster to the target, much like you wanted to shoot an arrow rather than cast a spell.

Glass is an obstruction. Mirrors don't produce a straight line. Remote viewing doesn't allow spellcasting unless a spell or magic item description explicitly says otherwise.

 

[greg kaye]

You have to have a clear path to the target. If using a mirror you don't have that.

... Mirrors don't produce a straight line. Remote viewing doesn't allow spellcasting unless a spell or magic item description explicitly says otherwise.

Many spells just have the requirement, "that you can see".
I'd have thought a reflected or magically enabled sight might facilitate this.

 

[Oofta]

Many spells just have the requirement, "that you can see".
I'd have thought a reflected or magically enabled sight might facilitate this.

There are be a few exceptions. Misty Step for example has a target of self and you teleport to an area you can see.

 

[Umbran]

Many spells just have the requirement, "that you can see".
I'd have thought a reflected or magically enabled sight might facilitate this.

You are, of course, free to run it however you like.

But, if you ask my opinion, for how I would typically run it - the mirror doesn't produce line of sight to the target any more than looking at the Moon gives you line of sight on the Sun.

 

[Lanefan]

I generally go with an unobstructed and straight line path from the eyes (or sensory organs) of the caster to the target, much like you wanted to shoot an arrow rather than cast a spell.

Which is for the most part the better way to do it, as it accounts for situations where you can't in fact see your target but you can still put a spell in its general direction e.g. casting a Fireball (or any other AoE or self-affecting spell, for that matter!) while in Darkness. I say "for the most part" because.....

Glass is an obstruction. Mirrors don't produce a straight line. Remote viewing doesn't allow spellcasting unless a spell or magic item description explicitly says otherwise.

.....while I agree with your latter two sentences, I'd say glass (and other invisible barriers e.g. a Wall of Force) is a different issue. With glass you have a straight line of vision provided there's light enough to see, which I'd interpret as making spells castable on a target behind the glass unless the spell required something physical to cross the distance between caster and target. Thus, a Fireball would wreck early when the glass stopped the little bead of guano while a Hold Person - which doesn't have anything physically go from caster to target - would work normally.

The only way around this would be to rule that the setting's physics prevent the transmission of magic through any intervening solid barrier; but that opens up a whole other list of in-setting headaches and inconsistencies.

I should ask: are there no spells left in 5e that in fact allow a caster to shoot blind e.g. to cast it behind a closed door just in case there's something there?

 

[Pedantic]

I'm just now realizing that this is yet another case I'm automatically subbing in 3e's rules without realizing, and relying on line of effect.

 

[ad_hoc]

If someone wanted to use a mirror to target a medusa with a magic missile I'm not going to say no.

 

[Tonguez]

If you use a mirror then the you would be targeting the image in the mirror not the actual creature. The actual creature would be obstructed.

That said I might allow a Spell Attack roll to simulate a Magic missile lazer being bounced off a mirror and giving the target 3/4s cover