Spellcraft is a skill that allows one to understand the general nature of 
magic. Its uses are twofold. By understanding the nature of magic one with 
spellcraft can identify the magic words required to cast spells and so 
always has a chance of knowing which spells are cast, even if they don't 
know the spell themselves. In addition, the knowledge of spells in general 
allows one with spellcraft to get greater use out of their mana, providing 
a discount on the cost of casting spells, and also increases the chance of 
spell success in non-combat situations.