Class, struct, or interface method must have a return type

error: error CS1520: Class, struct, or interface method must have a return type

script:

 public class Skill : ModifiedStat {
      private bool _known; 
     
     public Skill() {
         _known = false;
         ExpToLevel = 25;
         LevelModifier = 1.1f;
     }
     
     public bool Known {
         get{ return _known;}
         set { _known = value;}
     }
 }
 
 public enum SkillName{
     Melee_Offence,
     Melee_Defence,
     Ranged_Offence,
     Ranged_Defence,
     Magic_Offence,
     Magic_Defence
 }