From Istaria Lexica
Spells and weapons shown below may be useable as MulticlassInfo Spells.
However, you may lack the skill requirements on certain spells unless another school you've played delivers it.
- A Warrior does not gain the Life skill.
Any of the healing spells are based on life, so he is not able to use them on his own.
- A Cleric gets the Life skill.
If you did some levels as a Cleric and gained the appropriate minimum skill for a life based spell, you are able to cast it. Since Warrior is allowed to use some of the healing spells, too, you are able to cast them whenever you met the skill requirements.