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In this question, the Unseen Servant was somehow compared to a computer, which got me thinking. As a programmer, I know that a computer, although mindless, is very good at fulfilling conditional ("if something is true then do this, else do that"), sequential ("do this then do that") and looping ("do this while something is true", and "do this for that amount of times") tasks. Also, a computer is provided with a System Clock, and is therefore able to perform Waits. Therefore, this is a 7-in-1 question:

  1. Can an Unseen Servant fulfill conditional tasks? (ex : "pour wine into each empty glass" - in other words, if the glass if already filled, don't pour wine in it, else do it)

  2. Can it fulfill sequential tasks? (ex: "pour wine into my glass, then bring it to me")

  3. Can it fulfill looping tasks? (ex: "Pour wine into my glass every minute for 20 minutes")

  4. If it can do all three separately, can it do them all together? (ex: "Every minute for 20 minutes, for each empty glass, if it's empty, pour wine into it then bring it to their respective owner, else don't touch it")

  5. Can an Unseen Servant be fed a series of instructions via text (ex: "do what is written on this paper") or speech (ex: "do what any of my Magic Mouths will tell you to do when one starts giving orders" - so if you have several Magic Mouths, the trigger of the second Magic Mouth's speech might be something caused by one of the first Magic Mouth's instructions to the Unseen Servant... which essentially results in something like a function call in programming)? For this to work, the Unseen Servant must either have sight+reading abilities, or hearing+language abilities. The spell specifies you give telepathic commands to the Servant, but does not say if textual/verbal commands from your own voice work as well. The closest thing is a comparison to a human servant, so it might or might not work out.

  6. Can an Unseen Servant wait for a given time interval before doing a task step ? (how it would work out : as it takes a turn (6 seconds) for an Unseen Servant to move 15 feet, it therefore takes it 1 second to move 2.5 feet, so if you tell an Unseen Servant to move in circles for 2.5X feet before doing a step, then you essentially delay the step by X seconds)


As soon as I can, I'll put a big bounty on this question for the first person who puts a satisfying answer (either "yes" or "no", as long as the explanation is very good and all 7 questions are answered) because it's really important for me to get these answers.

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    \$\begingroup\$ I see you're casting the secret spell "Conjure Turing Machine"... very clever. \$\endgroup\$ – BlackVegetable Jul 3 '17 at 20:39
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    \$\begingroup\$ Can a mindless creature understand when a glass is empty? Or what a minute is? Does it even have ears to hear a magic mouth speak? \$\endgroup\$ – Ling Jul 3 '17 at 20:39
  • \$\begingroup\$ @Ling This could almost require its own question : what does "the best of its ability" refer to in the Unseen Servant's description ? Can it see, can it read (so can you order the Unseen Servant to read) ? Can it hear ? Etc. The only clue we have is a comparison with a human servant, which would make us think an Unseen Servant could have the 5 senses. However, you might also think that instructions are given mentally to the Servant, so it can't really hear anything on its own. Mystery, mystery... \$\endgroup\$ – Gael L Jul 3 '17 at 20:46
  • \$\begingroup\$ Historical Note: In earlier editions, an unseen servant explicitly could be commanded to perform simple, repetitive tasks, such as mopping a floor, without further caster intervention. \$\endgroup\$ – GMJoe Jul 3 '17 at 21:28
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    \$\begingroup\$ An unseen servant is about the intelligence level of Baldrick. \$\endgroup\$ – Greenstone Walker Jul 4 '17 at 0:45
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While not explicitly stated in the 5E Rules, a reading of the spell indicates that this it is capable of simple loops and simple sequences, but nothing more.

Based on the reading of the spell, it states this in terms of commanding it:

Once on each of your turns as a bonus action, you can mentally command the servant to move up to 15 feet and interact with an object.

Since we are considering this to be managed in a turn (6 seconds) and a Bonus Action only takes a small amount of that time...this implies that the time you have to command it is relatively short. And it indicates that you can tell it to move up to 15 feet and to interact with a single object. This does not sound like you can give it complex instructions.

This also shoots down the option to use a series of Magic Mouth spells. The Unseen Servant is commanded telepathically by the person who cast the spell. That is the only way listed that it can receive instructions.

It then goes on to specify that

The servant can perform simple tasks that a human servant could do, such as fetching things, cleaning, mending, folding clothes, lighting fires, serving food, and pouring wine. Once you give the command, the servant performs the task to the best of its ability until it completes the task, then waits for your next command.

This implies it is capable of understanding somewhat complex instructions, as serving food requires it to go get the food, then deliver it to where it is supposed to be. 'Fetching things' implies you can tell it something like "Go get me that book" and it would go to the book, pick it up, then bring it back to you without you having to walk it through every step of the process. Cleaning is a complex task that requires many steps to complete, and having to tell it "wipe that table, now that bookshelf, now the other shelf, now the other shelf" would be pretty useless. Same idea with mending things.

Furthermore, it speaks of a Task. Singular. You could tell it to fold that pile of laundry, and it would do so until it ran out of laundry to fold. You could tell it to clean a room and it would continue to work until the room was clean. But telling it to clean the room, then serve you dinner would be a pair of tasks...and it can only handle one task at a time. Exactly what counts as a 'Task' is up to DM Fiat.

So, to clarify my opening statement...

An Unseen Servant is capable of Simple Loops: It can be ordered to repeat a task multiple times until it has completed that task. If told to fold laundry, it will continue to fold the laundry until it has run out of laundry to fold. If told to clean, it will continue to move and clean things until it has finished. It cannot, however, perform Waits. As a mindless force, it doesn't have a System Clock like a computer. It has no concept of time.

An Unseen Servant is capable of Simple Sequences. That is, in order to complete a discrete task, it is able to undertake multiple different actions sequentially. "Pick up item from laundry pile, fold item, place item in folded laundry stack." It can, however, only be assigned a single task at a time.

A look back to the Unseen Servant of 3.5e supports this model. It can do one thing at a time, and will sequentially repeat that task until it cannot repeat it any more, or is commanded to stop.

Again, this is based off a reading of the 5E rules, with a smidge of 3.5e for precedent...there is NOT an official ruling on this.

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  • \$\begingroup\$ What if the task is to follow a series of instructions (steps) ? (to compare with programming, "task" = function, "step" = line of code) As you said, you don't have to guide an Unseen Servant into the many steps of a task. So if the task is to follow a series of instructions, it's just a bigger list of steps. As as for the bonus action timing, well... The task order takes little time to do by the caster (bonus action), but the task itself may take more than a turn ("performs until completed"). As for the concept of waiting... Good point. Don't know if an Unseen Servant can count seconds. \$\endgroup\$ – Gael L Jul 3 '17 at 22:18
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    \$\begingroup\$ @GaelL unseen servant is not programmable. It just comes with lots of builtin instructions to do mundane medival tasks. You can't just make your own. Also, it has no bufers, way low memory and very little registers. \$\endgroup\$ – Mindwin Jul 5 '17 at 10:11
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    \$\begingroup\$ @GaelL The key phrasing is "simple tasks that a human servant could do". If it would be plausible for an average household servant to understand and execute your command without requiring detailed instructions, the unseen servant can do it. The main difference to a real household servant is that the unseen servant can not multitask, because they can only execute one command at a time. \$\endgroup\$ – Philipp Jul 5 '17 at 11:49
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    \$\begingroup\$ Hmm... I command this unseen servant to CLEAN EVERYTHING. How literally do we take that? Will it set about cleaning the world? It's a specific, if illogical, task... \$\endgroup\$ – Isaac Kotlicky Jul 6 '17 at 0:41
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    \$\begingroup\$ @IsaacKotlicky It may attempt to do so...until its efforts take it more than 60' from you, and it winks out of existence. \$\endgroup\$ – guildsbounty Jul 6 '17 at 13:12
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Here's what I see as the relevant parts of the description of Unseen Servant:

This spell creates an invisible, mindless, shapeless force that performs simple tasks at your command until the spell ends. The servant springs into existence in an unoccupied space on the ground within range... Once on each of your turns as a bonus action, you can mentally command the servant to move up to 15 feet and interact with an object. The servant can perform simple tasks that a human servant could do, such as fetching things, cleaning, mending, folding clothes, lighting fires, serving food, and pouring wine. Once you give the command, the servant performs the task to the best of its ability until it completes the task, then waits for your next command

"Simple tasks" and the general 'one thing at a time' nature of the example tasks are the keys to most of the questions you pose, I think.

You can definitely loop a simple-enough activity

However, related questions on this site seem to indicate intricate conditionals are probably a step beyond what a "zombified" servant is reasonably considered capable.

"Mindless" is another aspect here to keep in mind, though the limits of it are definitely subject to interpretation and largely you should consult your local DM on whether building a Turing Machine out of concatenated Unseen Servants and other spells is even close to reasonable for the universe they are building.

An Unseen Servant only has a small amount of pressure to exert

So at any rate the Servant is almost certainly not operating some magical difference engine, unless all the fibers and spindles of the program-loom are gossamer-thin and feather-light -- and now it's possibly too intricate to manipulate without 'mindful' skill...

As far as simulating a Turing Machine goes, it might help to think of it as more like a complex musical instrument -- even if capable of playing a simple rhythmic instrument, the Servant would probably not be able to interact very 'effectively' with a device which is significantly more complicated.

A mindless-enough Unseen Servant might even accidentally break a more refined artefact (a more delicate and complex scientific or musical instrument.)

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  • \$\begingroup\$ The key thing I see in the spell restriction is that "simple tasks" is plural, hence why I believe the order you give can consists of sequential steps. But I might be wrong, hence the question. \$\endgroup\$ – Gael L Jul 3 '17 at 22:21
  • \$\begingroup\$ More specifically, the order might be a single task (ex : "bake a cake using this recipe") that is however composed of several steps ("crack the eggs", "pour flour in bowl", "pour sugar in bowl", "mix up all ingredients", etc.). \$\endgroup\$ – Gael L Jul 4 '17 at 15:11
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Mostly, no. An unseen servant is not a computer.

The capabilities of an unseen servant aren't precisely defined, mostly because precise definitions of spell effects that don't have direct game-mechanical interactions are typically left up to the DM and/or players to determine.

Given that, we should look at the likely intended flavor of the spell:

The servant can perform simple tasks that a human servant could do

That is, the kinds of things that a human servant in a quasi-medieval fantasy setting could do. "Human" and "servant" are both very relevant qualifiers here. A human can handle vague, open-ended, and qualitatively measured tasks in ways that simple computers cannot. Humans also have limits to their ability to count, repeat processes exactly the same way each time, remember things, and so on. A servant in this context is presumably competent in a number of domestic domains, and likewise ignorant in many other areas -- notably there would be no expectation of literacy or numeracy beyond simple counting.

Similarly, as a DM, I would expect the caster of unseen servant to instruct the spell as if it were a servant. Thus, these example questions from the question:

"pour wine into each empty glass"

"pour wine into my glass, then bring it to me"

"Pour wine into my glass every minute for 20 minutes"

"Every minute for 20 minutes, for each empty glass, if it's empty, pour wine into it then bring it to their respective owner, else don't touch it"

are neither the tasks an unseen servant would perform, nor are they tasks that a wizard would give. Instead, the wizard would tell the servant things like "Bing me a glass of wine", or "Keep our wine glasses full, but on no account should you open the '57 Clos du Montefort!". These tasks all implicitly involve evaluating conditions, chaining actions, looping, and other activities, but since the the servant performs them as a human would, the "computational" aspects of them aren't really what defines them.

More importantly, the unseen servant won't execute this kind of repeating, open-ended task in any kind of deterministic fashion. Maybe it will carry the bottle of wine around for a bit, topping up glasses as they are emptied. Then it might set the wine down and stay out of the way, or put the bottle of white back into the ice bucket. Maybe it will wait (as a good servant might) for a lull in conversation before interrupting with more wine. And so on.

As far as delivering instructions indirectly (for example "open the blue envelope in the next room, then follow the instructions written therein", or "obey the instructions of anyone wearing this hat"), the spell already limits the servant to following mental commands given by the spellcaster, and it seems reasonable to presume that the servant is illiterate.

An unseen servant can wait for a time interval ("Open the Cormyr red, then pour me a glass after it's had half an hour to breathe."), but it's no better at measuring the passage of time than a human servant, and only really useful when the waiting is related to a simple domestic task.

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Unseen servants are mindless. They cannot branch their instructions or think. Also the range of tasks they can perform are simple.

Can an Unseen Servant fulfill conditional tasks? (ex : "pour wine into each empty glass" - in other words, if the glass if already filled, don't pour wine in it, else do it)

Yes. It could also fetch buckets of water from a well and flood your wizard's tower if your apprentice was dumb enough.

Can it fulfill sequential tasks? (ex: "pour wine into my glass, then bring it to me")

That may be considered two commands. Assuming the servant is till in range after pouring the caster is assumed to automatically issues the second command if it is aware of the servant's status. The key part in the spell description is "interact with an object and move 15 feet" - so if it moves less than 15 feet it might be considered a single task.

Can it fulfill looping tasks? (ex: "Pour wine into my glass every minute for 20 minutes")

It is mindless, has no sense of time.

If it can do all three separately, can it do them all together? (ex: "Every minute for 20 minutes, for each empty glass, if it's empty, pour wine into it then bring it to their respective owner, else don't touch it")

Still mindless. Also that is three commands.

Can an Unseen Servant be fed a series of instructions (...)

Only if the mage is conscious, within range and playing the part of the feed tape. Servants have only one or two registers, no buffers and no RAM.

Can an Unseen Servant wait for a given time interval before doing a task step ? (how it would work out : as it takes a turn (6 seconds) for an Unseen Servant to move 15 feet, it therefore takes it 1 second to move 2.5 feet, so if you tell an Unseen Servant to move in circles for 2.5X feet before doing a step, then you essentially delay the step by X seconds)

It is mindless, has no sense of time.

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