Section 23 of the Indian Contract Act has specified certain considerations and objects as unlawful. The consideration or objects of an agreement is lawful, unless- it is forbidden by law; is of such a nature that, if permitted, it would defeat the provision of any law; or is fraudulent; or involves injury to the person or property of another; or the court regards it as immoral or opposed to public policy.
In each of the above mentioned cases the consideration or object of an agreement is deemed to be unlawful. Every agreement in which the object or consideration is unlawful is void.
X promises to obtain for Y an employment in the public service, and Y promises to pay X Rs. 1000 for that. This agreement is void as the consideration in this case is unlawful.
X agrees to let her daughter to hire to Y as a concubine. This agreement is void as it is immoral and as a result opposed to law.
The following agreements are considered to be against public policy:
Trade with the enemy:
An agreement between the citizens of two countries at war with each other is void and hence inoperative.
Agreement in interference with the course of justice:
All agreements which interfere with the normal course of law and justice are deemed to be opposed to public policy and hence are void.
Agreements which injure the public services are considered to be void.