In Y. B. 21 Edw. IV. 54, pl. 26, Choke, J., says : "If you are bound to enfeoff me of the manor of D. before such a feast, if you make a feoffment of that manor to another before the said feast, notwithstanding that you repurchase the property before the said feast, still you have forfeited your obligation because you were once disabled from making the feoffment." 77 This and similar statements are repeated several times in the early books.78

In Mommsen's Beitrage Zum Obli-gationenrecht, Abtheilung, 3,Sec. 4, it is ' said: "The obligation must be already due. So long as the time of maturity has not arrived, the obligor has always a defense in case the creditor should endeavor to enforce the obligation."

And in the typical case of one who regardless of his contract to sell and deliver in the future specific property to A sells and delivers it to B, Oesterlen, Der Mehrfache Verkauf, pp. 17, 18, says: "The temporary impossibility of performance due to the first delivery is wholly immaterial if it is removed at the proper time." . . . "When fulfilment is not made to the latter (i. e. A) at the proper time, then for the first time has a legal injury been done." On the other hand, prospective non-performance, though not giving a cause of action, is to some extent at least recognized as a defence in the Civil law. See infra, Sec.Sec. 906, 919.