A contract and agreement overcome the law.
Conventio Et Modus Vincunt Legem describes an elementary principle of law relating to contract i.e., a contract can be formed in a manner and agreement to overrule the law. The conditions added to a deed, rent or any instrument, regardless of whether composed or verbal went into between the gatherings, when appropriately executed and performed, have the power of law over the gatherings to the instrument. Where a right, obligation or risk would emerge under an agreement of clearance of merchandise by ramifications of law it might be negatived or changed by express understanding, or by the course of managing between the gatherings. The gatherings to an understanding may deny, reduce, or increment their rights by the terms in the understanding. Be that as it may, the gatherings to an understanding must decline the illicit contract.
The maxim Conventio Et Modus Vincunt Legem states that persons may contract themselves out of their legal obligations. It describes a situation where two or more people can enter into contract for overcoming the law.
When an agent is acting on behalf of the principal and binds the principal for some performance then in that cases the agent is not binding himself. However, if it is required for the agent to be liable then such contracts can be made separately.
In the case of Puttaswamy Gowda and others v State of Karnataka it was observed that When public premises is leased or sold or mortgaged to some persons, it is to be done only under the provisions of law. Leasing the property of the Government or Municipality or Corporation, which is a public property, shall be on the basis of distributive order and the persons of the society from different walks of life should be given an opportunity. When the premises is granted to a particular person, he has to utilise the same and shall also give an opportunity to other persons who are in queue. When an agreement is entered into between the parties in clear terms, the agreement prevails over unless it is alleged that the agreement itself is fraud, or etc. The maxim “Conventio et modus vincunt legem – A contract and agreement overcome the law; and Conventio privatorum non potest publico juri derogare – An agreement of private persons cannot derogate from public right” would apply in all fours to these cases. Under these circumstances, petitions fail and accordingly are liable dismissed.
In the case of Singh Ram (D) Through Lrs. v Sheo Ram and others the Supreme Court held that it is thus evident that the very conception of mortgage involves three principles. First, there is the maxim: once a mortgage, always a mortgage. That is to say, a mortgage is always redeemable and if a contrary provision is made, it is invalid. And this is an exception to the aphorism, modus et conventio vincunt legem (custom and agreement overrule law). Secondly, the mortgagee cannot reserve to himself any collateral advantage outside the mortgage agreement. Thirdly, as a corollary from the first, another principle may be deduced, namely, once a mortgage, always a mortgage, and nothing but a mortgage. In other words, any stipulation which prevents a mortgagor from getting back the property mortgaged is void. That is, a mortgage is always redeemable
Edited by Vigneshwar Ramasubramania
Approved & Published – Sakshi Raje
 Puttaswamy Gowda and others v State of Karnataka, 2016 Indlaw KAR 3138
 Singh Ram (D) Through Lrs. v Sheo Ram and others, AIR 2014 SC 3447