Greyhawk, added the Thief as a fourth main class, as well as the Paladin as a Fighting Man subclass. These four fantasy gaming archetypes represent four major tactical roles in play: the Fighter offers direct combat strength and durability; the Thief offers cunning and stealth; the Cleric provides support in both combat and magic; and the Magic-User has a variety of magical powers. In many ways, other classes are thought of as alternatives that refine or combine these functions. Each of the playable races had different amounts of access to the classes. Dwarves could be Fighters or Fighter/Thieves, with Fighter/Cleric possible for NPCs. Halflings were restricted to the Fighting Man and Thief classes. Elves were restricted to Fighter/Magic-User, Fighter/Magic-User/Thief, and Thief class options, with Fighter/Magic-User/Cleric an option for elven NPCs. Half-Elves (introduced in Greyhawk) could be Fighter/Magic-Users, Fighter/Magic-User/Clerics, or Thieves. All four non-human races had limited level advancement except in the Thief class. Humans could be any single class with no level restriction. Advanced Dungeons & Dragons 1st edition Advanced Dungeons & Dragons loosened the restrictions on race and class combinations, although non-human races often had restricted choices among classes and maximum levels they could reach in a class. Additional classes that had first appeared in supplements and articles in The Strategic Review magazine were included as base classes. The Player's Handbook also introduced the bard as a sixth base class; however, its usage in 1st edition was more akin to what would be called a prestige class in later editions, as it was not a legal choice for a starting character. Instead, a character had to start as a fighter, change classes to a thief, and finally switch classes once more to become a bard. A character's ability scores directly tied into what class choices were legal for them. For instance, a character wishing to be a fighter required at least 9 strength; the more discriminating monk required 15 strength, 15 wisdom, 15 dexterity, and 11 constitution. Unusually high or low ability scores could proscribe class choice further; "too high" an intelligence could prohibit being a fighter, while a charisma of 5 or less would require the character to become an assassin. High ability scores in statistics considered pertinent to the class would grant an experience bonus. The Player's Handbook brought about other changes in the game and its character classes. Fighters, clerics, and thieves have improved hit dice