A question, however, still remains, namely, is the first mortgagee to be placed in front, with the several other mortgagees, and the mortgagor behind him in the order of time, or is the mortgagor to be placed in front with the several mortgagees behind him in the reverse order of time? The answer depends upon whether the mortgagees and the mortgagor are to be placed with reference to the operations of the mortgages as transfers or assignments, or with reference to their operation as creating equitable obligations. If the former, the first mortgagee should stand in front; if the latter, the mortgagor should stand in front. And, as we are now considering mortgages, with reference to their operation in creating equitable obligations, it is clear that the mortgagor and the mortgagees should be placed with reference to that operation. Thus, we have the same final result, whether a succession of equitable obligations be created by successive mortgages, or by successive sub-obligations, though this result is produced by different machinery. In both cases there are as many equitable obligations as there are persons in the line, less one. In both cases every person in the line, except the first and the last, is both an equitable obligor and an equitable obligee, the first being an equitable obligee only, and the last an equitable obligor only. The only differences are, first, that, in the case of successive mortgages, each successive equitable obligation is made the subject of a new equitable obligation (i.e., of a sub-obligation), not by the original obligee, but by his assignee; and, secondly, that all the successive equitable obligations are made in favor of the same person, namely, the mortgagor, the latter always acquiring a new equitable obligation the moment that he relinquishes an old one.
There are still other modes in which an indefinite number of equitable rights may be derived from one legal right, namely: first, the owner of the legal right, instead of incurring one equitable obligation as to the whole of the legal right, may incur an indefinite number of equitable obligations, each as to some aliquot part of the legal right; secondly, the owner of the original equitable right may assign that right to an indefinite number of persons by assigning some aliquot part of it to each.
With respect to the modes in which they are created, equitable obligations differ widely from legal obligations. Most legal obligations are created by means of contracts; i.e., a person promises (expressly or by implication), or covenants to do or not to do