Here we see that, in order to entitle the assign to the benefit of the first grantor's warranty, assigns must be mentioned in the original grant and covenant. The scope of the ancient obligation was not extended without the warrantor's assent. But when it was extended, it was not by a contrivance like a modern letter of credit. Such a conception would have been impossible in that stage of the law. By mentioning assigns the first grantor did not offer a covenant to any person who would thereafter purchase the land. If that had been the notion, there would have been a contract directly binding the first grantor to the assign, as soon as the land was sold, and thus there would have been two warranties arising from the same clause,--one to the first grantee, a second to the assign. But in fact the assign recovered on the original warranty to the first grantee. /2/ He could only come on the first grantor after a failure of his immediate grantor's heirs. The first grantor by mentioning assigns simply enlarged the limits of his grantee's succession. The assign could vouch the first grantor only on the principles of succession. That is to say, he could only do so when, by the failure of the first grantee's blood, the first grantee's feudal relation to the first grantor, his persona, came to be sustained by the assign. /3/ [375] This was not only carrying out the fiction with technical consistency, but was using it with good sense, as fictions generally have been used in the English law. Practically it made little difference whether the assign got the benefit of the first grantor's warranty mediately or immediately, if he got it. The trouble arose where he could not summon the mesne grantor, and the new right was given him for that case alone. Later, the assign did not have to wait for the failure of his immediate grantor's blood, but could take advantage of the first grantor's warranty from the beginning. /1/ If it should be suggested that what has been said goes to show that the first grantor's duty to warrant arose from the assign's becoming his man and owing homage, the answer is that he was not bound unless he had mentioned assigns in his grant, homage or no homage. In this Bracton is confirmed by all the later authorities. /2/