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Intelligence (INT on your 'score' sheet) represents your character's mental
capacity, and determines how effectively your character can learn and reason.
Intelligence determines the number of distinct languages your character can
learn and it is the prime attribute of wizards, affecting how many
spells they can cast, how hard their spells are to resist, and how
powerful their spells can be.  In order to cast a wizard spell, the caster's
intelligence must exceed the level of the spell by ten.
 
You apply your character's Intelligence modifier to:
 
 - The number of languages your character knows at the start of the game.
 
 - Any skill or trade having Int as one of its prime attributes

 - How quickly you learn skills, trades, etc. through their use
 
 - Wizards gain bonus spells based on their intelligence scores
 
An animal has an Intelligence score of 1 or 2. A creature of
humanlike intelligence has a score of at least 3.
 
Any creature that can think, learn, or remember has at least 1 point
of Intelligence. A creature with no Intelligence score is mindless,
an automaton operating on simple instincts or programmed instructions.
It has immunity to mind-affecting effects (charms, compulsions,
phantasms, patterns, and morale effects) and automatically fails
Intelligence checks. Mindless creatures do not gain feats or skills,
although they may have bonus feats or racial skill bonuses.
 
Average Intelligence Scores
 
Example Race       Avg Int       Avg Mod
Zombie                -             - 
Purple Worm           1             -5   
Horse                 2             -4  
Gray Render           3             -4 
Griffon              4-5            -3 
Ogre                 6-7            -2 
Centaur              8-9            -1 
Human               10-11           +0  
Lamia               12-13           +1 
Wraith              14-15           +2
Beholder            16-17           +3
Mind Flayer         18-19           +4
Kraken              20-21           +5
Gold Dragon         32-33           +11