Armor Proficiency & Casting

[JeenLeen]

If my 1st level is Fighter, but then I multiclass into a full caster, like Wizard, can I still wear heavy armor and cast spells without any penalty? To phrase it another way, does arcane spell failure exist in 5th edition, like there was in 3.5?
I saw from the multiclassing rules that you don't get heavy armor proficiency if you multiclass into fighter, but it seems that multiclassing from fighter to a caster would make you a caster with heavy armor proficiency.

Also, what are the penalties for wearing armor one is not proficient in? Would that impact casting?
Is there any way divine and arcane magic differs? The distinction appears less important in 5th edition than 3.5 from the bit I've read.

[gfishfunk]

No arcane failure! If you have the armor proficiency from any source, it does not interfere with spell casting.

[BRC]

AFB, but if I recall.

1) Yes, starting as a fighter and multiclassing into a full caster gives you the armor proficiencies. However, it does NOT neccessarily give you the strength requirements needed to wear the heavier armor Types. As a result, you are either condemming yourself to a life of unoptimal MAD, or saving yourself a casting of Mage Armor each day. If you go Dragon Sorcerer, you don't even need the Mage Armor. There is no arcane spell failure, but you're now a wizard with squishy wizard hit points stuck in a metal can. Also, you just stalled your casting progression in exchange for an AC Bonus, so...congrats?

2) IIRC, Wearing armor you are not proficient in gives you disadvantage on everything physical, plus anything else your DM wants to throw at you.

So, to sum up, yeah, starting Fighter and multiclassing into Wizard works. But, it's not that big an advantage. To be a Mage in Full Plate, you're trading a level, plus 5 points of ability score (to get the 15 str you need to wear plate), in exchange for an AC bonus. Seems fair to me.

[Flashy]

If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can’t cast spells.

The specific text about what happens if you wear armor you aren't proficient with.

As other people have said though, starting with a level of fighter grants you heavy armor proficiency, so you wouldn't have a problem. It's not THAT advantageous though.

[gfishfunk]

Forgot to mention: wearing the armor without the proficiency causes you to fail at the somatic components of a spell.

[JackPhoenix]

Forgot to mention: wearing the armor without the proficiency causes you to fail at the somatic components of a spell.

Nope, that's 3.5 Arcane Spell Failure. If you're not proficient with armor in 5e, you can't cast spells in it, period (and it's the same for clerics and druids, not only arcane casters). Also, you take an disadvantage on ability checks, saving throws and attacks using Dex or STR

[SharkForce]

it is worth noting that not having the strength requirement for heavy armour merely slows you down. while that is certainly not desirable, it is also not *that* bad (and of course, you can always be a dwarf).

with that said, if you're only looking for proficiency in heavy armour, cleric (life, nature, or war iirc) is the best source of that for a wizard since you'll know a few more spells and keep full spell slot progression (even if you don't keep learning spells at an undiminished rate). fighter is good if you're also looking for, say, con save proficiency, second wind for a tiny bit of short rest healing, action surge, or a combat style, however; it isn't that a fighter splash is bad, it's just that if the only part you intend to use is armour, there are ways of doing that which give you more spellcasting.

[gfishfunk]

Nope, that's 3.5 Arcane Spell Failure. If you're not proficient with armor in 5e, you can't cast spells in it, period (and it's the same for clerics and druids, not only arcane casters). Also, you take an disadvantage on ability checks, saving throws and attacks using Dex or STR

Repped for the correction! (If rep were a thing here).

[tieren]

Nope, that's 3.5 Arcane Spell Failure. If you're not proficient with armor in 5e, you can't cast spells in it, period (and it's the same for clerics and druids, not only arcane casters). Also, you take an disadvantage on ability checks, saving throws and attacks using Dex or STR

Always makes me think that the best prison for wizards would be one that involuntarily keeps them in armor (maybe a chainmaill shirt with their hands manacled behind their backs). Also think about how much armor would be required to cause the "can't cast spells" to kick in, maybe you could get away with just using heavy plate gauntlets as the manacles themselves, or slapping a great helm ala Man in the Iron mask.