Bracton, who modelled his book upon the writings of the mediaeval civilians, shows how this thought was used.  He first puts the case of a conveyance with the usual clause binding the grantor and his heirs to warrant and defend the grantee and his heirs.  He then goes on:  “Again one may make his gift greater and make other persons quasi heirs [of his grantee], although, in fact, they are not heirs, as when he says in the gift, to have and to hold to such a one and his heirs, or to whomsoever he shall choose to give or assign the said land, and I and my heirs will warrant to the said so and so, and his heirs, or to whomsoever he shall choose to give or assign the said land, and their heirs, against all persons.  In which case if the grantee shall have given or assigned the land, and then have died without heirs, the [first] grantor and his heirs begin to hold the place of the first grantee and his heirs, and are in place of the first grantee’s heir (pro herede) so far as concerns warranting to his assigns and their heirs [374] according to the clause contained in the first grantor’s charter, which would not be but for the mention of assigns in the first gift.  But so long as the first grantee survives, or his heirs, they are held to warranty, and not the first grantor.” 1

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