A more ancient institution, the gamos di' agoras, whereby the future husband had to pay for the acquisition of his wife, was replaced by the gamos di' engyes. The engye, or pledge, was simply the contract between the wife's kyrios and her future husband. It was contracted by mutual promise that the woman in question would be handed over by the former and would correspondingly be honoured as his spouse by the latter. Handing her over was, however, a completely separate act. The marriage had substance only if there was cohabitation. On the other hand, for there to be cohabitation worthy of marriage and not to be regarded merely as concubinage, it was essential that the pledge should have been given in advance. At least from the time of Solon, and thereafter, the pledge was a sine qua non for the legality of the marriage. Concubinage (pallakeia), though obviously lower than marriage, was nevertheless socially acceptable. There was in fact a legal framework to define the relation of the concubine and the children she brought into the world with her kyrios.