Does this mean that a character who starts out with a single level fighter (or any other class with heavy armor proficiency) can from then on gain levels as wizard and forever more cast spells, without any penalty whatsoever, while wearing full plate? For example, Diatonic Sorcerers get permanent Mage Armor for free at 1st level, which provides 13 + Dexterity Modifier AC.
If you take a mage with high Dexterity, then it only gets worse as the armor gets heavier. In addition, any mundane armor heavier than 20 pounds will give you Disadvantage on Stealth checks, and truly heavy armor won't let you apply your Dexterity Modifier at all.
Furthermore, the only spell casters who have access to meta magic (which, aside from magic gear, was the primary way ASF was mitigated) are Sorcerers, which is also the class that needs heavy armor the least. Magic gear is much harder to come by now, so the likelihood of you finding a magic suit of armor made to be light and maneuverable is much more remote, thus removing yet another way of mitigating ASF.
It is not unbalanced because the there are many ways to increase the AC of a Wizard, from Mage Armor to bracers of defense etc. Of course, you'd be better off taking 1 level of war domain cleric, but the cost of dipping in regard to stat improvements or feats is still there.
It's not a departure from D&D tradition, because in all versions, if you picked the right combinations you could negate the arcane spell failures for all intents and purposes. The only people who missed out were those who lacked the system mastery to create the character concept.
On the other hand, the generic wizard always had a hard time casting spells in various types of armor, and in this edition is not merely difficult, but impossible to do so unless you choose the correct rule combinations, which allows you to do so. $\begingroup$Metal interferes with the correct and proper flow of MANA.
This could manifest itself in a number of ways, perhaps the armor gets magically charged and this causes discharges of power that are very dangerous. Metal disrupts the Weave, causing dead zones and preventing wizards from accessing it properly and casting spells correctly.
It will actively impede their movement, make them fatigued, and distract them from the fine concentration necessary to cast magic. While warriors are wearing armor, getting it properly fitted, and tuning their bodies for it, magicians are studying.
If a mage were to spend time practicing in armor then they would miss out on spell study. Just having armor on, with no knowledge of how to move in it, use it to block hits, or the stamina to wear it for long while running around won't lead to the armor class improvement” seen in game systems.
But will a mage character spend a precious skill on armor instead of a more directly useful magic feat? Even boiled leather or quilted armor, while not that bad when wearing it in the comfort of your house, quickly becomes a big nuisance when you wear it all day tramping through the woods.
To address some comments to my answer, I believe in an RPG system, armor class is more than just passive resistance. Sure, you could drape a chain mail shirt over someone and presumably it may protect from an arrow hit (kind of like how journalists or prisoners wear ballistic armor today) but in a fight being unfamiliar with wearing armor means you won't react appropriately.
Movies love to show a belly slash with a sword against someone wearing mail as being a lethal attack, but in reality that would be worse than useless as it would just dull your sword edge. Rigid armor sets are even worse, they need to be tightened in specific ways and are usually worn over a bulky padded under layer.
So a mage unfamiliar with wearing not just armor, but a specific set of armor, is going to find that a certain set of gestures won't work while casting a spell in combat to potentially disastrous results. Clearly things like bulky winter clothing shouldn't interfere with spell casting (unless you really want to penalize casters) so there is a bit of hand waving.
Though presumably folks in cold climates have their winter clothes and have practiced in them, modifying jackets and such to allow for proper spell casting. The least restrictive clothes to allow for the precise gestures and movements required.
But unless casting spells involves yoga positions or something similar it is a little of a logic tweak to say that padded or leather armor will interfere with casting but a heavy woolen jacket wouldn't. You could spend a day and a bunch of money getting it custom fit, but without years of fighting practice a wizard in plate is barely more protected than one not in plate as the weight of plate would throw off their reactions, make them easy to knock over, and they wouldn't know which vulnerable areas to protect and what areas they can use to block an attack.
For faint signals you need precise design and as my uncle the engineer (who built them) it became more of a black art than science. So your mage, when young, deals with big whomping spells and as he progresses has to be more and more aware of the surrounding metals.
Besides, if you are tossing lightning about, a big metal shell is not the greatest idea. In this case, the magi would be inside the chain mail metal suit, which would make a perfect Faraday cage.
There are you-tube videos of people wearing chain mail suits while Tesla coils send out million volt lightning bolts all around them, even striking the armor. So if the process of generating the power to create the magic came from some form of electromagnetic energy (drawing lightning from the sky, for instance) the chain mail would prevent it from reaching the magi in order to be harnessed.
Nature magic and leather armor are fine as the druids and shaman will explain. Metal is heavy, mages tend to spend more time in the library than the gym and hence would have some considerable trouble moving around in 40lbs of armor.
Metal is a wonderful conductor of heat and often doesn't respond well to extremes of temperature. Some metals freeze and shatter, or contract excessively when cooled.
Necromancers are an entirely different game from your average frost and fire mages. So its this corruption of an immutable natural form that gives iron (as well as any metals of your choosing)its anti-magic properties.
You need to provide an incentive to not wearing armor by making it affect the areas where your wizards are especially good. If you need different types of mages where some are capable of using armor and others are not you could vary the kind of rituals.
A war mage might in fact need to spend at least 4 hours every day in full plate armor. It helps him concentrate and brings him into a mental state where he is able to quickly react to any danger.
When he takes off the armor he suddenly feels all the tiredness of the day and becomes far less capable of using his magic. $\begingroup$If you don't need to worry about it for reasons of balance (which I'm going to assume is the case since you're asking here and not the RPG.stack) why not put the cart before the horse.
A new apprentice who still hasn't mastered basic protection spells might need to wear armor while learning them or practicing combat magic. This has also led to a bit of a stigma on wearing armor ; If a wizard is wearing armor most other wizards (or in the know folk) will assume she hasn't mastered protection spells yet, so a prideful mage may go unarmored even when they haven't quite mastered protection spells to avoid the embarrassment of others learning of their lack of skill.
Finally, most opponents won't even try to stab a wizard without some sort of magical blade, due to the potentially lethal nature of common magical defenses which leads to some perfectly capable, but slightly lazy wizards not bothering to cast their magical defenses every day (security through obscurity). Thus, wizards just don't have the strength to wear decent strong (and therefore heavy) armor.
In some very specific cases, armor like this could be beneficial, but only if it is a rare creature of magical energy, and only if the caster only wants to cast one type of spell (that associated with the creature's energy). The armor still causes the spell to lose power, and thus have a chance of not working, but is also tainted by the energy of the creature the skin came from.
The wand is typically made out of conductors made of animal remains or metal because then the downsides of armor can be focused as positives, by conducting the power to a singular point of focus. Yes, in this universe the magical energy is part of the world, but fireballs don't just spontaneously erupt from the sky.
Breaking the normal physical rules requires not just that you say the right words, and perform the correct gestures, but that you actually believe that the ritual will have the intended result, and that you personally can control causality. A skeptic performing the ritual with technical perfection but not believing it will do anything will produce no results.
Wearing armor is an implicit acknowledgement of that risk, thus on a subconscious level undermines the belief that you are in control. Wearing simple robes is acceptable because that isn't about protection or control, it is about modesty and keeping up cultural norms.
Culturally people are taught from a young age that wearing armor is incompatible with casting spells, it has become part of the zeitgeist, it is accepted lore. In a culture where everyone wears armor, not for protection, but for style, or tribal identity, or rank, then 1 won't apply.
If they were confident enough in their skills, they could wear it as an intimidation tactic: “I am so powerful the normal rules do not apply to me. One could become deranged and actually believe that armor and magic are still incompatible for normal people, but I'm special.
$\begingroup$I've been beaten to the punch regarding the “iron has anti-magic properties” thing so instead, here's an alternate explanation based on one of the other rules: You can throw around fireballs, create walls of earth, fly through the sky, ...
Maybe a smaller, well-placed pillar of earth to knock the guy's sword arm out of the way. Alternately, maybe a “Shield” spell exists, that creates a protective sphere around the caster.
This mechanism also adds a neat approach to the lore behind retaining spells. You can recognize a high-level wizard because there seems to be a slight wind going through his robes at all times, and you see a magical spark-light effect if he holds a shield for too long as the energies struggle to escape him and are aided by the shield's interference.
Clerics don't draw magic in through their bodies, they're given it by their gods, sort of like they have a breathing tube. And druids, if we want to allow them leather, have a more efficient mechanism of drawing magic that isn't blocked by non-metal armor, but only allows them to draw in very specific types of magic that can permeate through leather.
Those effects are really rough on things like heavy armor, often reducing it to an unusable state after only a day or two of a standard adventurer's workload of spell casting. Higher-powered mages can afford this better, but they also throw around more powerful spells, which means it tends to happen (much) faster.
Basically, while they technically could wear armor, it's not worth it for the sheer cost of keeping the stuff repaired... and that means that it's not worthwhile for the mages to learn to wear the armor properly in the first place. Independently wealthy mages have also died a time or two in the past when their armor got warped by spacial magic into a cage of inward-pointing spikes.
Additionally, not all armors are metal, and hide armor can still can interfere with spells. The more armor you wear, the more likely that a given body part you might need to “open” up to the ether via gesture to draw power is covered and less likely to get you into the proper position to complete a spell.
For example, perhaps your spell gestures require you to place your hand on a central chakra/chi node/magical organ, simply, you have to touch your chest. Wearing armor means you can 't effectively complete this gesture, and even some thick leather might occasionally catch you up in the complex act of tapping into arcane energies.
Note that in fantasy settings there frequently are beings with powers beyond that of the gods. They may be called “Era”, “AO” or “Dungeon Master”; in any case they are beyond caring for the worship of mortals, and care mainly for maintaining a form of balance.
It is in their interest to ensure that the universe is not dominated forever by a single wizard with mind control and necromancy powers. Thus, they shape the arcane powers to give wizards at least one Achilles heel, so there is always hope that such a tyrant would be overthrown.
Although wizards draw on the arcane power created by the over deity, they have no need to pray. Never-the-less the rules of reality that, so limit wizards were created by an over deity with an explicit interest in balance.
$\begingroup$There's nothing forbidding a caster to wear heavy armor ... unless they want to boil inside the breastplate. That's because channeling MANA through our bodies is quite an exothermic reaction, and it's easier to bear if you're wearing light-fluffy wavy clothes.
$\begingroup$Depending on your setting there might simply be some analogy to the Geneva Conventions in place prohibiting mages from wearing armor at all. A historical example of such deliberate restrictions can be found in medieval times.
We prohibit under anathema that murderous art of crossbowmen and archers, which is hateful to God, to be employed against Christians and Catholics from now on. The armor might refract the magical energy too, into directions that are difficult to control.
If the staff had a magical wave speed that was in-between the wave speed of the user's body and the air, then there would be less reflection at the boundary between the magic user and the air and so there would be less energy lost in casting the spell. Movement: You need precise control of mind, spirit and... body.
Yet...) It takes pure materials and “good” energy to make proper clothing for a mage (in addition to heavy materials being bad and impure materials actually blocking magic)... that's why silk is better than wool... and why druids are known to dance naked under the full moon. Magic pulls that energy through you... last thing you want to do is be grounded... (Further note: Don't use swords.
(Edit) I suddenly get an image of a mage with a parabolic metallic reflector cowl behind his head. It could be the souls of those capable of wielding magic are vulnerable to influence from spirits (ex: the main villain of the first book of the Inheritance series, Dragon, was overwhelmed by spirits).
Could be, every magic sensitive in the realm is provided abjuration protecting against spiritual assault. The natural physical abjuration might weaken the spiritual one, like a drug interaction, leaving the magician vulnerable to having his or her mind consumed.
Or, it might be that the (pure) unbound body, robes of rank, and other accouterments are a usually-not-talked-about somatic and material component to most (if not all) magic. This pulling in ideas from modern physics where particles communicate light (photons), gravity (gluons), and mass (Higgs).
Could be a scary armor scares away, or a strong natural abjuration drives away the spirits of most utility to the average magic practitioner. This could also help explain magic poor areas (if they exist in your world).
But this approach is a supernatural restatement of the “metal short circuits/Faraday cages magic electricity” suggestion. To do that, we could simply say that wizard robes are woven of a special material, say, unicorn hair.
While there might be metals with the same capacity to conduct MANA, you could easily restrict that property to the most special, but also most clumsy metals, like gold or also plectrum, a melding of gold and platinum present in many fantasy universes. Mikhail is often used as a metal that's very lightweight and incredibly sturdy, and certainly you'd have a hard time to justify it cannot conduct MANA since it's one of the unique materials in existence, but it's also incredibly rare.
In most fantasy stories where Mikhail is present, only the most skilled dwarves metallurgists are able to produce it, let aside the fact that the needed metals are among the rarest as well. And as a matter of fact, you don't even need to include Mikhail in your universe (although most people would probably be a little bummed if you didn't).
Their primary offense is magic and, while they might use weaponry, they are probably best advised to run away because they will be facing those much better trained and, in any case, a good (or even mediocre) wizard is far more valuable than an ordinary soldier. Their best defense for most practical purposes is to hide behind something like a wall or in a good solid tower.
Light armor may help, if necessary, to protect a wizard out in the open from ranged weapons but may be counter-productive if it significantly slows him in running for cover or prevents him from crouching behind whatever may give protective shelter. Just as spells can not pass thought armor (unless it is specialized for it) when it hits the hard material, such as metal, the spell takes effect (just like when electricity reaches a component in a circuit).
Staves are not made from metal, because it stops the energy from flowing (electricity ground), while formerly alive materials such as wood or bones are used to flows of magical energy. Mail armor mesh could stop the flow of energy from the caster, just like a cage does for electrical discharge.
With added size and weight, there is a chance, that the spell will discharge into the caster and not the intended target. Many magic systems require some sort of sense, to cast the spell successfully.
In my world I compensate for this with using rare highly conductive materials (MANA crystals, gold, silver) or using enchantments and runes, to artificially infuse the material with magic and thus making it conductive. $\begingroup$If we try to apply game rules to the in game universe logic wizard spell casting is primarily a mental exercise as indicated by dexterity not being of no relevance as could be expected if intricate and complex set of movements is required.
In addition, not all spells in the wizards list have somatic components I. E don't require movement and in fact some bards can ignore the adverse effects of armor presumably because their spells are “simpler”. The other side has enchanted swords, and they will cut through your unenchanted armor like butter.
From the little things, protective magic placed on them by midwives, mothers, fathers. Wizards are people who collect magical secrets in the form of spells.
In order to cast these spells, any enchanted items you have on you have to be taken into account. The armor that a wizard must wear is enchanted with effects that help them cast their spells, and the “weapons” (staffs, wands, orbs) likewise.
Wouldn't do him much good against anything other than hail stones, as any crude dagger used by an urchin with even a modest enchantment makes your plate armor useless. They either use a different form of magic/spells, and/or they have unique enchantments on their armor /weapons that permit both weapon use and magic use.
Such “spell swords” may not be able to cast as powerful a spell given the same level of training as a traditional wizard. The reputation requirement helps protect this question from spam and non-answer activity.