Oblivion:Alteration

Alteration is the magic of altering the physical world.  It provides many useful effects that can make up for other character weaknesses, for example: Open can be used instead of Security to open locks; Feather can be used if your Strength is too weak; Shield can be used instead of armor.  In addition, Water Breathing and Water Walking provide valuable capabilities.

In-game Description: Cast spells to breathe or walk on water, open locks, shield from physical and magical damage, and alter encumbrance.

Mastery
Mastery Perks
A Novice can only cast Novice level Alteration spells.
An Apprentice can cast Novice and Apprentice level Alteration spells.
A Journeyman can cast Journeyman, Apprentice and Novice level Alteration spells.
An Expert can cast Expert, Journeyman, Apprentice, and Novice level Alteration spells.
A Master can cast all Alteration spells.

Skill Benefits
As your Alteration skill increases, the Magicka cost to cast alteration spells decreases, according to the following equation:
 Cost = BaseCost * (1.4 - 0.012 * Skill)
The maximum value for Skill in this equation is 100; increases past 100 will not continue to decrease spell-casting cost.

Skill Increases
You gain 4 experience points every time an alteration spell is cast upon an appropriate target, regardless of the magicka cost.

General tips for increasing spell-casting skills are provided at General Magic Strategies.

The best standard alteration spell for practice is Protect: it is the second-cheapest alteration spell, and since it is cast on self you can always repeatedly cast it to gain experience. The cheapest standard alteration spell is Open Very Easy Lock, however it is less convenient as a training spell because you need a lockable object to practice on (note that the object does not actually have to be locked, so any door or chest will work).  

To create a custom practice spell, by far the best effect to use is Feather.  It is the cheapest effect in the entire game, so a 3pt 1sec Feather spell costs almost nothing to cast.  The only limitation of the Feather effect is that you must be apprentice level to be able to cast the lowest-level standard Feather spells (Ease Burden, or Buoyancy).

See also:
Increasing Skills: General tips on how to improve your skills semi-naturally.
Trainers: Pay for alteration lessons.
 
Skill Books: Books that provide lessons in alteration.
Increasing Attributes: Tips on training skills to improve the Willpower attribute.
Magic Items: There are multiple generic items with the fortify alteration enchantment.
There are no Unique Items that fortify the alteration skill. These do not include Leveled Items such as those received from quests, or Artifacts.

There are no Free Skill Boosts available for Alteration.

Dialogue
When your skill reaches 70 or higher, NPCs will start saying: "You look skilled in Alteration.  Maybe you can teach me something."

Character Creation
The following races provide initial skill bonuses in alteration:
+5 bonus: Bosmer, Breton
+10 bonus: Altmer

The following standard classes include Alteration as a major skill:
Battlemage, Healer, Mage, Monk, Nightblade, Sorcerer, Spellsword

If you choose Alteration as one of your major skills, you will start with two Alteration spells: Open Very Easy Lock, and Protect.

Magical Effects
A list of all standard alteration spells can be found on the Spells page.  The following individual effects are all considered to be part of the school of Alteration (see the individual effect pages for full details on availability; the Magical Effects article also provides a summary):


Note that unlike earlier Elder Scrolls games, the alteration effect of Levitation is not available in Oblivion.

Messages
The following table provides the messages that are displayed when your Alteration skill levels up.



Notes
The Cheydinhal Mages Guild specializes in alteration; Trayvond the Redguard and Orintur sell the most alteration spells.
Once your combined Fame and Infamy reaches 50, you can visit the Magnus heaven doomstone to receive the greater power Skein of Magnus.  One of several benefits of this power is that it fortifies your alteration skill 15 points once a day for 120 seconds.