I don't think a player can or should play a character whose intelligence differs from his own. (This won't prevent any player from playing a scholarly character, as players in real-life are already smart enough to handle it.) Playing a dim character is unfair because the player's ability to solve problems would be stifled, and playing a smarter character is probably impossible. Nonetheless, if someone wishes to play a stupid or brilliant character, the rules won't stop him; the player simply notes the PC's intelligence on his sheet. NPCs and lucid monsters will have an INT rating; other monsters would be rated for cunning. I'll have to go over my draft more thoroughly, but WIL (willpower) should be able to substitute for INT in most/all cases (e.g., for memory and ability to learn).