The Philosophy of Law: Private Right, § 21: Acceptance and Delivery
A thing is not acquired in a case of Contract by the ACCEPTANCE (acceptatio) of the Promise, but only by the DELIVERY (traditio) of the object promised. For all Promise is relative to Performance; and if what was promised is a Thing, the Performance cannot be executed otherwise than by an act whereby the Acceptor is put by the Promiser into possession of the Thing; and this is Delivery. Before the Delivery and the Reception of the Thing, the Performance of the act required has not yet taken place; the Thing has not yet passed from the one person to the other, and consequently has not been acquired by that other. Hence the Right arising from a Contract, is only a Personal Right; and it only becomes a Heal Right by Delivery.
A Contract upon which Delivery immediately follows (pactum re initum) excludes any interval of time between its conclusion and its execution; and as such it requires no further particular act in the future by which one person may transfer to another what is his. But if there, is a time—definite or indefinite-agreed upon between them for the Delivery, the question then arises, Whether the Thing has already before that time become the Acceptor’s by the Contract, so that his Right is a Right in the Thing; or whether a further special Contract regarding the Delivery alone must be entered upon, so that the Riiht that is acquired by mere Acceptance is only a Personal Right, and thus it does not become a Right in the Thing until Delivery? That the relation must be determined according to the latter alternative, will be clear from what follows.
Suppose I conclude a Contract about a Thing that I wish to acquire,—such as a Horse,—and that I take-it immediately into my Stable, or otherwise into my possession; then it is mine (vi pacti re initi), and my Right is a Right in the Thing. But if I leave it in the hands of the Seller without arranging with him specially in whose physical possession or holding (detentio) this Tiling shall be before my taking possession of it (apprehensio), and consequently before the actual change of possession, the Horse is not yet mine; and the Right which 1 acquire is only a Right against a particular Person—namely, the Seller of the Horse—to be put into possession of the object (posccndi traditionem) as the subjective condition of any use of it at my will. My Right is thus only a Personal Itight to demand from the Seller the performance of his promise (prccstatio) to put me into possession of the thing. Now, if the Contract does not contain the condition of Delivery at the same time,—as a pactum re initum,—and consequently an interval of time intervenes between the conclusion of the Contract and the taking possession of the object of acquisition, I cannot obtain possession of it during this interval otherwise than by exercising the particular juridical activity called a possessory Act (actum posse ssorium) which constitutes a special Contract. This Act consists in my saying, ‘I will send to fetch the horse/ to which the Seller has to agree. For it is not self-evident or universally reasonable, that any one will take a Tiling destined for the use of another into his charge at his own risk. On the contrary, a special Contract is necessary for this arrangement, according to which the Alienator of a thing continues to be its owner during a certain definite time, and must bear the risk of whatever may happen to it; while the Acquirer can only be regarded by the Seller as the Owner, when he has delayed to enter into possession beyond the date at which he agreed to take delivery. Prior to the Possessory Act, therefore, all that is acquired by the Contract is only a Personal Uight; and the Acceptor can acquire an external Thing only by Delivery.