**HYPOSTASIS**
It is the transcription of the Greek word ὑπόστασις, which shares the same etymology as the Latin *substantia*, *subsistentia*, and *suppositum*, and literally signifies that which stands beneath, that which underlies the flux of appearances, that which is posited by thought beneath phenomena. It is a highly important theological term whose meaning was clarified through lively controversies within the language of the Church, the Fathers, and Scholastic philosophy.
Apart from the common meaning it had in popular and literary usage, in Greek philosophy and among the Fathers it first signified the proper essence of a thing, as a synonym of οὐσία: what a thing truly is, its fundamental and specific content—its own nature (φύσις). *I.* was therefore also synonymous with nature, conceived as the foundation of all the properties of a thing, as the principle of its specific activities. In St. Paul it signifies foundation (cf. *of the things hoped for*, Heb 11:1), principle (*the image of his substance*, ibid. 1:3), and also essence.
Secondly, in Greek philosophy and among the Fathers, it came to mean “he who has subsistence, or essence, or nature,” thus becoming synonymous with an existing individual or person.
When the Fathers sought to express the notions of Christian mysteries in terms of common language, they found themselves faced with possible misunderstandings and were compelled to give the terms a more proper and precise meaning. Thus, in the mystery of the Most Holy Trinity, the word *i.* became a source of ambiguity: it could be misunderstood as implying three essences or substances or natures (Arian heresy), or as implying a single nature subsisting as a person (Sabellian heresy). Hence St. Jerome could say that in the word *i.* there lay hidden poison (Epist. XV, to Pope Damasus). The Synod of Alexandria, in 362, left it open to each believer to profess either that in God there is one *i.* or that there are three *i.* precisely because of the double sense of that word (essence-substance and person). Yet one could not remain in ambiguity, and it was the clarifying work of the Fathers, against the ambiguities of the heretics, to attach a precise technical meaning to the terms. Thus *i.*, distinguishing itself from οὐσία and φύσις, assumed the proper meaning of an individual subsisting in and of itself, i.e., of a person, and the Trinitarian dogma received its definitive orthodox formulation: one οὐσία or φύσις (substance or essence or nature) in three *i.* (three persons).
Similarly, in the formulation of the mystery of the Incarnation, misunderstandings arose if the sense of *i.* was not well defined. If it was taken in the sense of οὐσία and φύσις, one had to say, to remain orthodox, that in Christ there are two *i.*, for to say that in Christ there is one *i.* would affirm the fusion of the human and divine natures, falling into Monophysitism.
If, instead, it was taken in the sense of person, one had to say, to remain orthodox, that in Christ there is one *i.*, so as not to fall into Nestorianism.
By defining the meaning of *i.* as that of person or entity subsisting in and of itself, the orthodox formula of the mystery of the Incarnation was fixed thus: in Christ there is one *i.* (the divine person, the Word) and two οὐσία or φύσις (the divine and human natures); hence the union of the Word with human nature was called a *hypostatic union* (cf.).
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**I. NATURE AND FOUNDATION**
In social exchanges of goods, it is not always possible to give the agreed-upon price; it is reasonable that in such a case, the giver be guaranteed to receive what is due, for the very continuity of exchanges. For matters of little importance, the word of a known and honest person suffices; but in the case of substantial sums, of poorly known persons, or of an unnamed creditor (a company), an objective guarantee is required, especially since even prudent individuals may face unforeseen financial setbacks due to force majeure. Hence the origin of various real guarantees. Among these is *i.*
The system of guarantees in contracts was already known to Eastern peoples and the Greeks, though the nature of these guarantees is debated due to a lack of texts. Among the ancient Romans, *fiducia* and *pignus* were used; later, with the increase of exchanges, *i.* was introduced as an improvement upon *pignus*; however, it had two defects: it lacked publicity and was limited only to the instruments of cultivation introduced by the tenant into the leased land. An improvement occurred in the Justinianic era. Modern law began to introduce publicity and specificity toward the early 17th century, but general introduction occurred in the last century. England has *i.* with a somewhat different character (*mortgage*).
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**II. IN ITALIAN CIVIL LAW**
The nature of *i.* as a real immovable guarantee right, constituted over specific goods of the debtor or a third party, is derived from arts. 2808 et seq. of the Italian Civil Code (cf. also arts. 2740); here the creditor is given the right to expropriate the good, even against a third-party acquirer, for the purpose of satisfying the debt, with preference over other creditors who are not privileged. In Italian law, *i.* can be legal, judicial, or voluntary.
1) **Constitution.** — All commercial immovable goods with their appurtenances can be mortgaged, as well as certain immovable real rights (superficies, usufruct, emphyteusis); among movables, government bonds, ships, aircraft, and motor vehicles (art. 2810). For its constitution, a title and registration are required.
In some cases, the law grants *i.* (legal: arts. 2817). Such is recognized for the seller over the goods alienated for the fulfillment of obligations arising from the act of alienation; for co-heirs and co-sharers for the payment of adjustments over the immovables assigned to other co-sharers; for the wife over the husband’s goods as security for the dowry; for the State over the goods of the accused. Judicial *i.* is granted by the judge in any sentence that condemns to the payment of a sum, the fulfillment of an obligation, or compensation for damages. In any contract with a voluntary agreement, *i.* can be constituted (voluntary), if the owner of the good grants it with a unilateral declaration in a public or authenticated deed, excluding a will (arts. 2821 et seq.).
For civil effects, registration in public records is mandatory; indeed, the effects begin with registration.
In every office of the land registers, there is an official designated as the "registrar of records" (conservatore dei registri), who is entrusted with the duty and responsibility of keeping the land registers up to date (cf. arts. 2852 et seq.; 2843; 2847-2851; 2882; 2873; 2875; 2882).
The properly registered land interest (i.) is valid for twenty years (art. 2847). If the interested party fails to renew it, they forfeit their rights; however, they may obtain a new registration, valid from the new date (art. 2848); this does not apply to the land interest in guarantee of a dowry (art. 2849).
2) Rights of the creditor, the debtor, and the third-party acquirer. — The creditor: a) in the event of the debtor’s default, may satisfy their claim by requesting, at the agreed maturity, the foreclosure of the mortgaged property, even if it has meanwhile passed to third parties. b) In relation to other unprivileged creditors (art. 2745 et seq.), they have the right of priority, so as to be able to satisfy the entire claim. It is important to consider the rank of the land interest among multiple mortgage creditors.
The debtor, if they possess the property, must not be disturbed; they may collect the fruits until maturity, and may redeem the land interest by satisfying their own obligation.
The land interest (i.) may also be granted in favor of the debtor by a third party over the latter’s own property (third-party giver of the land interest); or it may happen that, after registration, the mortgaged property is alienated to a third party (third-party acquirer). This third party is subject to the mortgage creditor’s enforcement action, since the land interest is a real right. However, being personally uninvolved in the debtor-creditor obligation, the law grants them certain facultative rights: they may pay the creditor directly, thereby becoming a creditor of the debtor in turn; they may free the property from the land interest by offering the creditor the price stipulated with the other party; or they may surrender the property to foreclosure, with the right to compensation from the debtor (arts. 2858-287).
3) Several land interests may be constituted over the same property; in such a case, the rule “prior tempore potior iure” applies, with the time being calculated from the date of each registration according to rank and order (arts. 2852-287). This gives rise to subrogation or subrogated mortgage.
The land interest is extinguished by cancellation, failure to renew, extinction of the principal obligation, destruction of the property, renunciation by the creditor, expiration of the agreed term, or fulfillment of a resolutive condition (art. 2878). If the debt is reduced or the value of the mortgaged property increases, the land interest may be reduced, provided the property allows it (arts. 2872 et seq.).