I'm a little confused by some of the spell/enchantment effects in the game, so I was hoping someone might be able to make sure I'm getting these right.

1. Weakness to Magic: As I understand it, afflicting someone with 100% Weakness to Magic essentially means they will take double damage from a magic spell during the duration of the effect. If this is the case, doesn't this make it much cheaper to double the damage of a spell by simply making a custom version that does "Weakness to Magic" right up front? That seems to add less to the magicka cost than actually doubling the magnitude. In the case of a Shock damage spell, it seems like you could even triple the damage by adding 100% Weakness to Shock while you're at it, no?

Also, the UESP wiki seems to imply that Weakness to Magic (and NOT other weakness effects) stacks. So could you enchant a dagger with 100% weakness to magic on strike for 3 seconds, strike a few times quickly, and then hit with a spell that does damage on touch to wildly magnify its effects?

2. Shield/Resistance/Armor Rating: I notice that when I wear clothing enchanted with Fire/Frost/Shock resistance, it boosts my stated armor rating in the inventory screen, despite that this stuff doesn't actually have a Shield effect on it. Is this an error, or do Fire/Frost/Shock resistance actually also count toward your base armor value? (And if that's the case, why ever cast Shield spells when you could cast element-specific spells and also cut down on elemental damage?)

I had a couple other questions, but I'll just offer those for now and come back as needed. Thanks in advance!

Weakness to magic does what it says, but it must be in effect before the attack. That is a spell with weakness to magic and damage, both for one second is a waste of the weakness to magic. You have to weaken them before you damage them. So if you make the weakness for several seconds, it can help you on the second cast, or you you can use two spells.

Your dagger idea can work fine since weakness to magic (unlike other weaknesses) does stack. Your dagger has weakness to magic 100 x 3 secconds. Hit your foe quickly several times then zap them with a damage spelll before the three seconds is up.

Shield = just armor rating
Element (fire, frost, shock) resistance = just resistance to that element.
Element shield = armor rating + resistance to the element in question. It is obviously superior; that is why it 'costs' more to use.

Is it resist fire/frost/lightning, or Lightning/fire/frost Shield. The lightning/fire/frost Shield is basically aegis, and makes you more powerful against that specific type of magic. Resist magic, i dunno.

I think that clears everything up. Thanks!

My other, unrelated question was whether you could cast a spell with Drain Attribute: Intelligence to effectively Silence someone, but it looks like Silence is simply more magicka-efficient. Took me a while before I was even able to use Drain Attribute effects in making spells, though...