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Can you use Minor Illusion to create an illusion of a working mirror, i.e. with a working reflection?

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closed as primarily opinion-based by GMJoe, user17995, LegendaryDude, Oblivious Sage, KorvinStarmast Mar 31 '16 at 2:41

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Okay, let's not start asking and answering new questions in the comments. Anyone have a new question inspired by this, please do post it! \$\endgroup\$ – SevenSidedDie Mar 30 '16 at 22:56
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    \$\begingroup\$ Looking at the answers, it seems clear that people are coming to different conclusions on this based on their own ideas on how light (and magical illusions) work. The rules don't actually provide a clear answer to this question - so I'm voting to close as Primarily Opinion-based. \$\endgroup\$ – GMJoe Mar 31 '16 at 0:25
  • \$\begingroup\$ I have something I believe provides a clear answer to this and uses RAW to justify it rather than use opinion about physics and light etc. Could this question be re-opened so I can post the answer please? \$\endgroup\$ – Protonflux Nov 16 '16 at 12:21
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According to the description:

You create a sound or an image of an object within range that lasts for the duration. The illusion also ends if you dismiss it as an action or cast the spell again.

If you create a sound its volume can range from a whisper to a scream. It can be your voice, someone else's voice, a lion roaring, a drum beating or any other sound you choose. The sound continues unabated throughout the duration or you can make discreet sounds at different times before the spell ends.

If you create an image of an object such as a chair, muddy footprints or a small chest-it must be no larger then a 5 Foot cube. The image can't create sound, light, smell or any other sensory effect. Physical interaction with the object reveals it to be an illusion, because things can pass through it.

With this in mind - I would say no. Minor Illusion is very limited (e.g. static), and cannot produce any side effects (e.g. no light, or other sensory effects). I expect this also means the light would pass through the illusion, and that maintaining the same properties as the physical version of the object is beyond the scope of the illusion. This is mostly because its not actually a real object (e.g. it does not behave like a mirror), it only looks like one.

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    \$\begingroup\$ Hmm... I'm not sure that the bolded text really applies to what's going on here. Mirrors don't create light, they reflect it. Besides, by this reasoning one could tell the difference between any illusion of a sufficiently reflective surface and the real thing (such as a polished helmet): no reflections! \$\endgroup\$ – Tophandour Mar 30 '16 at 16:48
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    \$\begingroup\$ If light passed through an object then it would be invisible. Light bounces off of visible objects, that's what makes them visible. The only thing special about a mirror is that light is reflected at the angle of incidence, rather than being scattered randomly. \$\endgroup\$ – John Kugelman Mar 30 '16 at 17:31
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    \$\begingroup\$ @JohnKugelman It's a valid argument, but nothing about the magic implies that it is actually visible (as in obeying the properties of physics re: reflecting/scattering photons), only that the unknowing perceive it to be real. It exists only in your mind, the illusionist is bending the light/weave in order to trick you, etc. Also, without going too deeply into physics.SE territory, keep in mind that light == matter, thus if things can pass through the illusion because it is not real, so too can light, lending further credence to the fact that the illusion doesn't actually exist. \$\endgroup\$ – LegendaryDude Mar 30 '16 at 20:47
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    \$\begingroup\$ @LegendaryDude Plus, viewers who know it's an illusion can see through it. That solidly torpedoes any argument that rests on assuming it reflects light like an independent object would. \$\endgroup\$ – SevenSidedDie Mar 30 '16 at 22:54
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    \$\begingroup\$ Historical note: Earlier editions (some of them, anyway) made a clear distinction between illusions that existed only in characters' minds, and illusions that were more like holograms in that they existed in the world despite being intangible. The question of whether mirrors had reflections wasn't directly addressed, but knowing that both sorts of illusions had historical support might be useful to anyone making a ruling about this. \$\endgroup\$ – GMJoe Mar 30 '16 at 23:33
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Yes, because physics.

The simple fact that you can see an illusion means it reflects light, whether it is the illusion of a mirror or not [edit: see below].

Note that this does not violate the rule that “The image can't create sound, light, smell or any other sensory effect.” The image is not emitting light, it is reflecting it. An illusion of a mirror would act no differently than the illusion of anything else - it just reflects the light perfectly, allowing the viewer to see an image.

Objects that do not reflect light (at all) look like a perfectly flat, black surface. So if illusions are to be useful in any way, they must reflect light.

[Edit]: I will concede that if illusions are a purely mental construct, like an hallucination, that physics will not apply; however, in that case my answer is still yes, because if we're tricking the mind we can surely trick it thoroughly.

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    \$\begingroup\$ You may want to expand your reasoning to establish a base argument that illusions cannot create the illusion of self-illumination, since it's generally accepted that they can do so, and your answer relies on the premise that they cannot. \$\endgroup\$ – SevenSidedDie Mar 30 '16 at 17:51
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    \$\begingroup\$ +1 I wish more people understood that ALL visible objects reflect light... they just scatter it more randomly than a shiny object (like a mirror) does! \$\endgroup\$ – Matthew Mar 30 '16 at 18:31
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    \$\begingroup\$ -1 Illusions do not need to obey the laws of physics. They are magic, and might as well be a figment of your imagination (because they quite literally are). \$\endgroup\$ – LegendaryDude Mar 30 '16 at 20:52
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    \$\begingroup\$ @Escoce By that logic, illusions wouldn't change in appearance due to changes in lighting - which means you could detect any illusion just by holding a candle to it. This seems weird to me. So many illusions that adventurers encounter are in dark dungeons, and in dark dungeons adventurers carry light sources. Every illusion would stand out like a sore thumb due to remaining unilluminated even when the adventurers approach it, or by being illuminated in a dark place even before they approach. \$\endgroup\$ – GMJoe Mar 30 '16 at 23:43
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    \$\begingroup\$ +1. The only ways to see an illusion are that a) it reflects light so your eyes can see it, b) it generates light so your eyes can see it (specifically contradicted by the rule), or c) it's a totally a figment in peoples' mind mimicing a real object, in which case a mirror would act like you expect a mirror to. \$\endgroup\$ – mxyzplk Mar 31 '16 at 2:35
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No.

There are two ways you could think about the reflection. You could imagine it as an effect created by the caster - a constant modification in reaction to the movement of objects around the "mirror" - but that would imply the constant attention of the caster. But that stands in contradiction to the fact that the spell does not require concentration. (It doesn't seem that any motion in the visual images is allowed, although some flexibility with sound illusions is given.)

Alternatively, you could imagine that the image has the property of being able to reflect light - that is, it is a physical mirror. But this is a physical interaction, and "Physical interaction with the image reveals it to be an illusion, because things can pass through it." This may seem a little strange, since we intuitively assume that we can perceive illusions in the same physical way that we perceive actual objects - that is, ambient light reflects from the surface of the illusion and reaches our eyes. But this intuition is apparently wrong. Illusions do not reflect ambient light - if we discern the illusion it becomes faint to our sight, so clearly most or all ambient light actually passes through the illusion. Furthermore, different observers may see different images, depending on whether they discern the illusion, so the process cannot be as deterministic as conventional science would demand. The physics are not explained, but clearly they are different from what we are used to in the mundane world.

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I am going to say no, and here is why.

Minor illusion allows you to mimic simple things. However it does not duplicate effects. Although a mirror is a simple thing, the images it reflects are or could be very complicated. Additionally, they'd need to mimic what's being reflected in mirror image.

I think you could use minor illusion to mimic a portrait, but s mirror I think is too complicated.

Ok, I am pulling out the boom to refine my answer, but that's this is still the basis.

Update: nevermind, shadow players answer is good.

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No, one cannot create a mirror illusion with this spell, because reflection requires matter interacting with light-stuff (called photons in our reality) and the collision causes them to change direction (which we call either reflection or refraction depending on how focused the effect is). While several of the answers above point out that illusions are visible, I would like to humbly point out that illusions are a form of magic often relegated to a school centered on light-production and light-manipulation, not creating matter that then interacts with light on its own.

If I conjure a brown wooden table, then that table reflects brown light while absorbing other hues. When the lights go out the table has no light to reflect, so it is, for all intents and purposes, impossible to see. However, an illusory table is not solid like the conjured one; it is a preprogrammed construction of light that is specifically defined as impossible for matter to interact with. That would mean it cannot reflect or absorb light; light passes through it and it is technically transparent. The only reason we can see it is because it is producing light.

The way I read the description, at the time of casting the spell, the caster must decide exactly what they wish to present, and that is the amount of continuous light the object produces. Not only would such an illusion be easily spotted due to a lack of reflection, any change in the lighting of the room would not cause the object to lighten or darken – it would stand out because it is fundamentally incapable of reacting to its environment in the way actual matter is. In a dark room therefore it would glow.

This does however raise several mechanical issues. Any and all light that would come into contact with the object instead passes through it. So if I simulate a five foot box then I can see within the box using light that passes through the illusion from outside, but I cannot see what is outside. Likewise if I light a torch within the box then those outside will see the box emitting torchlight from within. I believe a similar issue arose when my group contemplated the possibility of an invisible light source. You see exactly what the spell says you can see (in this instance whatever the caster decided upon at casting time) and then apply lighting effects as if the spell were not in effect.

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  • \$\begingroup\$ So... You're saying the rules for illusions don't make sense and are contradictory? \$\endgroup\$ – GMJoe Mar 31 '16 at 4:58
  • \$\begingroup\$ No, I believe I said that the rules for illusions say that, unless otherwise specified, they are light-based constructions that do not interfere with matter or light in any discernible way. An illusion of a blindfold prevents you from seeing through it, but not from being hurt by looking at the sun, because light passes through it. \$\endgroup\$ – Benjamin Mar 31 '16 at 15:55
  • \$\begingroup\$ Although, now that I think about it, my interpretation of the spell does not mean that matter cannot interact with the illusion, simply that matter passes through it. This would make for some very interesting (and hard for a GM to describe) visual effects when an illusion interacts with an actual mirror or prism. While the objects technically pass through they also can interact with the light-stuff. \$\endgroup\$ – Benjamin Mar 31 '16 at 16:20
  • \$\begingroup\$ You say "at the time of casting the spell, the caster must decide exactly what they wish to present, and that is the amount of continuous light the object produces." The spell specifically cannot create light. \$\endgroup\$ – LegendaryDude Mar 31 '16 at 16:59
  • \$\begingroup\$ Not in the sense of creating useful light, in the same way a torch would, but in the sense that it would be oddly visible from some distance away. Magic often glows even when it does not specifically "create light." If my memory serves, many enchanted objects did in the first three editions of d&d were technically supposed to glow when in use (although we often threw that rule out because it didn’t make sense). I believe this page dealt with the subject of illusory light versus actual light: rpg.stackexchange.com/a/56429/27248. \$\endgroup\$ – Benjamin Mar 31 '16 at 17:14

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