I'm aware that Ignem technically includes "light" effects.
But the species emitted by an Imaginem effect are mundane, so no longer magical.
Could you create an Imaginem torch and have it illuminate a darkened room? It's probably easier to use Ignem of this purpose, but I'm just curious if what I propse is feasible.
I always ruled that images do not create ilumination.
So while you could create the image of a torch it would not shed light. You could also create acompanying images of the torch's suroundings but without some other method of determining what the illusionary torch's surroundings look like you'd be hard pressed to reproduce the surroundings accurately.
In my experience when you split images and illumination into unrelated entities all sorts of sticky rules issues go away. (Well one sort of sticky rules issue goes away.)
Nope. Illusions neither shed light nor cast shadows unless you construct them to look like they do.
Is there somewhere in the text that states or suggests this? Or is this an inference you've drawn from other sources?
Imaginem does not create the sense impression themselves, but it influences how objects emanate these impressions. In terms of a scientific anachronistic example - it does not create the radiation itself but rather it changes the radioactive material that radiates the radiation. Hmmm... confused? Good. This radiation, as opposed to the material that is its source, is called species.
Thus the species require light rather than create it, and since the Imaginem only holds power over the production of species at the "originating body", it cannot create light.
This fits finely with the fact that Ignem is the Form of light and that mutual exclusive cathegories are preferable.
Thank you for that very complete reply. Very helpful.
MY Verditius is an imaganem specialist so I have read alot on this.
Species are "emitted" by objects. It states in the RAW (not sure of page) that "sight" species need light to travel. So without actual light, the "sight" species would not go anywhere, and no one would see them.
Remember in this paradigm (that word), light reflecting off objects and being recieved by the eye IS NOT the cause of appearance. Species being emitted from an object and being "carried" by light to the eye is the cause of appearance. So light is like a boatman, but species are the cargo. You must have both to get the package (appearance) to the viewer.
It is often weird to do the disconnect between the modern scientific view of how the world works and the hermetic view. This sort of question comes up with Rego alot due to the lack of momentum and Newtonian inertia in the hermetic view.
Just to clarify paridigm for me...Is darkness
a) an absence of light
b) radiated by objects
c) Caused by the objects obsorbing all the light available
Darkness is absense of light. The reason you can't see is that the sight species can't get to your eyes because there is no light to carry them there.
The absense of light. Light is a potentiality that is best described as a transparant media for the species - or colours - that emanates from visible objects. On a sidenote you could flip the term translucent upside down. Light is not something that passes through - it is rather something that allows for something else, the colours, to pass through it, the light.
In the words of Aristotle (On the Soul):
Since light to the ancient philosophers had to be divided into the basic 4 elements, they spend time discussing what senses belonged to what of the elements. Some argued that because of the need for light, the sense of sight had to be the sense connected to fire. Aristotle argued against this (On Sense and the Sensible ) - since water puts out fire, how come the light from the sun is not put out when it rains or when there is frost? Ergo - the sense of sight could not be fire! He argued that the sense of sight was based on water (the eye) but that light was needed for the potentiality of the colours reaching the eye.
Great job, as always, Furion. Great quote.
Cheers mate! Thanks for the kind words 
I am actually not very wise on Aristotle, but he is great in terms of finding in-setting ways of explaining things in Ars. It is however somewhat anachronistic. Partly because many of the classics of Greece were lost to Europe untill they made their way back in the later middle ages in the form of Arabian translations of Greek works. That means many of the works and thoughts of the ancient philosphers might not have been known to them. And partly because the scholastics of the middle ages actually either had or developed another take on how perception worked than Aristotle's. That the eye did not just passively receive the species, as wax imprinted with a seal, but that the eye was active in "catching" and bringing in these impressions. Or maybe alike a lantern. In many ways these thoughts mirrored some of Aristotle's contemporaries, who's thoughts he argued against in his works.
I think it is perfectly alright to "create" light with imaginem.
You might remember the "Phantasmal Fire"-Spell, CrIm20? It does NOT have an Ig-Requisite. (well, at least in 4th Ed.)
So you can create the image of a torch, will shed light, but you probably couldn't create an unseen source of light as you could with Ignem.
Imaginem and the other arts overlap.
Your Imaginem-creations come from the world of ideas, not the world of facts.
A phantasmal fire is as realistic as the casting magus imagines it. It will hurt to put your hand in it, tough your hand wont be burnt. The quality of the pain will depend on the magus 'hands-on-experience'. Ouch!
You could create the scent of flowers with Imaginem instead of Auram, but if you were allergic to those flowers, the scent wouldn't make you sneeze.
Illusionary food certainly tastes, but won't satiate.
And so on...
As Imaginem does never even touch the essential nature of its target, you can do almost anything. Such as disguising a man as a woman, which wouldn't be feasible with Corpus.
There is no need to make imaginem spells physically correct, they just need to be believeable. This is the one big cutting edge of Imaginem. And its one and only reason to exist.
Sometimes you will need to enhance Imaginem-Spells with a Mentem-Requisite, to make them more believeable. e.g. to give the image of a peace of chainmail some weight.
Other requisites may be helpful to add realism to your effects where necessary, or to make up for a lack in finesse.
Requisites might allow for "half-real" imaginem effects.
Imaginem overlaps with most of the other arts. That's sometimes troublesome, but necessary if you want Imaginem to be of any use in the game.
I guess I slightly broadend the topic...
Hope i was any help.
Hi Fury,
Welcome aboard! Nice to see new people, moreso when the furious kind(!)
I do however disagree with you on the matter of Imaginem. You can read my arguments above, so I won't repost them.
Actually it does have a Ignem requisite in 5th. And often it is difficult to extrapolate the mechanics from 4th to 5th precisely because 5th was given a lot of thoughts on how to improve aswell as streamline the rules.
All Creo spells draw on the realm of ideas, hence the 'perfection' and unblemishness of created object. Imaginem differ in the way that it doesn't create anything tangible, but only an intagible source of 'species'(the species are not magical in themselves).
That would actually be feasible with Corpus. What the Limit of Essential Nature limits is not the possible effects - such as turning a man into a woman - rather it works to ensure that you cannot do so permanently. It would always be temporarily since the man's nature is.. well.. being a man! Therefore the duration will run out and he will return to his Essential Nature, and during the duration he can be changed back by not only MuCo spells but also by a Vim spell to remove the magic keeping him in his unnatural state.
we've always ruled it as quite simply:
Real Light (Ignem) stimulates objects to emit visual species. Observers receiving these species discover what the objects look like from this.
False Light (Imaginem) "paints" species over the scene. These can be species of any appearance the caster desires... they can paint the "room as it is" but ONLY if the caster knows what is there and paints that.
Imaginem does not discover anything new - it overlays the real properties with the spell-species.
So... an illusion of a Torch can spread an illusion of a flickering patch of colour near to itself. This implies the presence of a wall ... but the "wall" is only there because the caster willed it into the spell.
Equally they can use the Illusion-of-torch to actively and deliberately deceive those looking into the scene.
Harumpf... something to immediatly house-rule out, should my troupe upgrade.
I do not like the thougt that an illusionist needs to be able to cast BOAF to be able to use visual Imaginem-effects at night. It just feels wrong to me.
In fact, it seems you can't even create an illusion of a torch, since the blurb on species (p. 79) indicates that visual species need light to propagate: "while those for sight require light to get any distance from the originating body". So if the room is dark, your illusory torch should not be visible at all.
In the Hero System Rules , Illusions are defined as either Mental (all in the mind) or as Light-based Images that can be manipulated.
Ars Magica has neither of these concepts for Imaginem effects.
This is more in line with Mentem Magics , because the Mind of the caster is involved ,
he has to "imagine it" and use his memory to create the intensity of the experience.
Well. YMMV. I am a very big fan of 5th, although I also have a couple things not entirely in my favour and thus house rule material, but one of the things I particularly like about 5th is the great revision of the magic system. In that light you would find that many spells have changed Technique or Form and that the guidelines are much streamlined. I like that the Arts are mutual exclusive in what they cover and dont cover, and in this case I really like it alot that the rule mechanics are explained with and by insetting terms.
And frankly, an illusionist does not need a BoAF. If needed be he can stick to adding an Ignem Casting Requisite in most cases. I can only think of one situation when you'll need to add light to an illusion - since most people around who would see it in the first place would have light of their own - is when you need the light more than you need the illusion, in which case it's only a poor excuse not to learn the very very rudimentary Ignem needed to create light.