What is a 1½-handed weapon?
The 1½ -handed weapon is actually a 2-handed weapon, but it can be used with one hand. If a medium 1½-handed sword is used with one hand only, the sword is no longer treated as a medium weapon; the sword will be treated like it’s a large weapon. You’ll need to spend 3 Actions when using it in combat just like using a large weapon; you’ll need to use the Large Melee Weapons Skill instead of Medium Melee Weapons Skill, but you can hold a shield or another weapon in your other hand.
1 ½ – handed weapons are excellent choices for Player Characters who plan at training Skills for both medium and large weapons.
1 ½ – handed weapons are perfect for Player Characters who don’t plan on using shield in combat, but still want the advantages of using a medium weapon.
Player Characters who generally rely on Strength and Armor would maybe consider a 2-handed weapon instead; its heavier, deals more damage, but requires more actions to use.
Most people, who plan on choosing other Skills than just combat related Skills, would in general be more than happy with a quick 1-handed weapon, and maybe a shield.
The choices are yours to make when using the Insight RPG System.