Contract is formal insofar as the two acts of consent, through which the common will comes about — the negative moment of alienating a thing and the positive moment of accepting it — are distributed between the two contracting parties; — a contract of gift. It can, however, be called real insofar as each of the two contracting wills is the totality of these mediating moments, so that each thereby likewise becomes and remains an owner; — a contract of exchange.