Using larger weapons

I've looked into the rules and can't seem to find rules regarding characters using large size category weapons and yet... Amiri relatively pathfinder's posterchild barbarian uses a large weapon though it is stated only whilst in rage form. What goes on?

I assume you are referencing Pathfinder and not some other game?  The rules you are looking for are on Core Rulebook page 144: Inappropriately Sized Weapons.  In short, you can use weapons larger than your size provided they are not turned into bigger than 2-handed weapons.  Amiri is using a Large Bastard Sword. A Bastard Sword is a 1 handed weapon that if you do not have the exotic weapon proficiency to use it counts as a 2 handed weapon.  In order to use a large Bastard Sword you need to have the exotic weapon proficiency and use it in two hands. You also suffer a -2 attack penalty.  - Gauss

Cullen P. said: I've looked into the rules and can't seem to find rules regarding characters using large size category weapons and yet... Amiri relatively pathfinder's posterchild barbarian uses a large weapon though it is stated only whilst in rage form. What goes on? Weapon Size : Every weapon has a size category. This designation indicates the size of the creature for which the weapon was designed. A weapon's size category isn't the same as its size as an object. Instead, a weapon's size category is keyed to the size of the intended wielder. In general, a light weapon is an object two size categories smaller than the wielder, a one-handed weapon is an object one size category smaller than the wielder, and a two-handed weapon is an object of the same size category as the wielder. Inappropriately Sized Weapons : A creature can't make optimum use of a weapon that isn't properly sized for it. A cumulative –2 penalty applies on attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. If the creature isn't proficient with the weapon, a –4 nonproficiency penalty also applies. The measure of how much effort it takes to use a weapon (whether the weapon is designated as a light, one-handed, or two-handed weapon for a particular wielder) is altered by one step for each size category of difference between the wielder's size and the size of the creature for which the weapon was designed. For example, a Small creature would wield a Medium one-handed weapon as a two-handed weapon. If a weapon's designation would be changed to something other than light, one-handed, or two-handed by this alteration, the creature can't wield the weapon at all. <a href="http://paizo.com/pathfinderRPG/prd/equipment.html#_table-6-5-tiny-and-large-weapon-damage" rel="nofollow">http://paizo.com/pathfinderRPG/prd/equipment.html#_table-6-5-tiny-and-large-weapon-damage</a> When he rages his bonuses probably outweigh the penalties so that is why he only uses it when raging.