one house is subjected to another, one piece of land to another. Thus they are  called urban and rural servitudes. What they are, who may institute them, in  whose favour and how, and if they have been constituted how they may be lost,12  will be explained below.13
Of acquiring the dominion of things by gift inter vivos.
 Since the most celebrated and famous of the causae acquisitionis is that of gift it  may lay claim to pride of place, for in that way more is acquired, and acquired more  often, than in any other. Hence we must first see what a gift is and into what  divisions it falls; who may give and who may not; [then] what may be given and  what not, and to whom a gift may be made and to whom not. Then the requirements  of a valid gift. Then how possession may be acquired and how transferred from one  to another; [and finally], when it has been acquired, how it may be lost, and when  lost how recovered.
What a gift is.
 A gift is a disposition arising from pure liberality and without legal compulsion,  14that is, neither of civil or natural law, payment, duress or force playing no part.15  It proceeds from the full and free disposition of a donor [wishing] to transfer his  property to another.16 To give is to make a thing the property of the taker  effectively,17 otherwise it will be useless, as a gift made of another's property18  which may be invalidated and revoked, for he who obtains possession in such a way  that he cannot retain it is not considered to have gained it at all.19 Nevertheless,  if another's property is given the gift will be valid from the first as between donor  and donee,20 though invalid as against the true lord, him who has the right,  against whom it will never be valid except by the confirmation of him who may  invalidate it, that is, the true lord himself or his heir, as by their ratification, or  by the lapse of time which bars all actions.21
How gifts are classified.
 We must see how gifts may be classified. They may be classified as follows: some  are inter vivos, some mortis causa, that is,22 by reason of a testamentary causa,  which will be explained below.2324Some gifts are simple and absolute, where the  donor does not wish what he has given or promised to give to revert to himself,  whether the gift is made absolutely or to take effect at some future day; others are  made ob causam, where a causa is put into the gift that something be done or not  done, into which class fall gifts causa dotis and causa mortis25 and the like. [It is  simple and absolute] unless the gift is made subject to a condition or modus,26  as where 27one gives with the intention that the thing will become the donee's  only when
24-25. Azo, Summa Cod. 8.53, nos. 2-3: Quae sit donationum divisio? Et quidem alia est simplex, alia ob causam; simplex est cum nullo casu velit ad se reverti quod dedit vel quod se daturum promisit, sive fiat pure sive in diem sive sub conditione; ob causam est quae interponitur ut aliquod fiat vel non fiat in quam speciem dico cadere donationem propter nuptias et causa mortis et dotis.
26. nisi fiat ... sub modo, from line 31; infra 50, 66, 82, 106
27-28. D. 39.5.1: dat aliquis ut tunc demum accipientis fiat cum aliquid secutum fuerit: non proprie donatio appellabitur, sed totum hoc donatio sub condicione est. Item sum quis ea mente dat ut statim quidem faciat accipientis, si tamen aliquid factum fuerit aut non fuerit velit ad se reverti, non proprie donatio dicitur sed totum hoc donatio est quae sub condicione solvatur, qualis est mortis causa donatio.; Woodbine in Yale L. Jour., xxxi, 833-4