Final answer:
An agreement is considered illegal when its formation is a crime or a tort, its performance is a crime or a tort, or it is contrary to public policy.
Step-by-step explanation:
An agreement is considered illegal when:
- Its formation is a crime or a tort
- Its performance is a crime or a tort
- It is contrary to public policy
- All of the above
In other words, an agreement can be illegal if the act of forming it or carrying it out is a crime or a tort, or if it goes against established public policy. For example, agreements to commit illegal activities like drug trafficking or fraud would be considered illegal.