Mayne's Hindu Law and Usage, Twelfth Edition, page 329 Custom must be ancient, certain and reasonable as is generally said. It will be noticed that in the definition in Cl. (a) of Section 3 of the Act, the expression 'ancient' is not used, but what is intended is observance of custom or usage for a long time. The English rule that 'a custom, in order that it may be legal and binding, must have been used so long that the memory of man runneth not to the contrary' has not been strictly applied to Indian conditions. All that is necessary to prove is that the custom or usage has been acted upon in practice for such a long period and with such invariability and continuity as to show that it has by common consent been submitted to as the established governing rule in any local area, tribe, community, group or family. Certainty and reasonableness are indispensable elements of the rule. For determination of the question whether there is a valid custom or not, it has been emphasized that it must not be opposed to public policy. I shall deal with the question of public policy later on. The origin of custom of adoption assumes great importance. The origin of custom of adoption is lost in antiquity. The ancient Hindu Law recognized twelve kinds of sons of whom five were adopted. The five kinds of adopted sons in early times must have been of very secondary importance, for, on the whole, they were, relegated to an inferior rank in the order of sons. Out of the five kinds of adopted sons, only two survive today; namely, the. Dattaka form prevalent throughout India and the Kritrima form confined to Mithila and adjoining districts. The primary object of adoption was to gratify the means of the ancestors' by annual offerings and therefore it was considered necessary that the offerer should be as much as possible a reflection of a real descendant and had to look as much like a real son as possible and certainly not be one who would never have been a son. Therefore, the body of rules was evolved out of a phrase of Saunaka that he must be 'the reflection of a son'. The restrictions flowing from this maxim had the effect of eliminating most of the forms of adoption. (See Hindu Law by S. V. Gupte, Third Edition at pages 899-906). The whole law of Dattaka adoption is evolved from two important texts and a metaphor. The texts are of Manu and Vasistha, and the metaphor that of Saunaka. Manu provided for the identity of an adopted son with the family into which he was adopted. (See : Manu.Chapter IX, pages 141-142, as translated by Sir W. Jones). The object of an adoption is mixed, being religious and secular. According to Mayne, the recognition of the institution of adoption in early times had been more due to secular reasons than to any religious necessity, and the religious motive was only secondary; but although the secular motive was dominant, the religious motive was deniable. The religious motive for adoption never altogether excluded the secular motive.