When is there co-ownership? There is co-ownership whenever the ownership of an undivided thing or right belongs to different persons. What governs co-ownership? The Civil Code provides that co-ownership shall be governed primarily by contracts, or special provisions. In their absence, it shall be governed by the title on co-ownership in the Civil Code. Some of the rules are discussed below. What is the presumption with regard to the portions belonging to the co-owners? The presumption is that the portions are equal, unless the contrary is proved. What is the rule with respect to alteration of the thing owned in common? The rule is that all the co-owners must consent to the alteration before any co-owner can make alterations in the co-owned thing. Alterations include any act of strict dominion or ownership and any encumbrance or disposition has been held implicitly to be an act of alteration. The construction of a house on the co-owned property is an act of dominion. It may be deduced that no person can construct a house on the thing owned in common without the consent of all the co-owners. May a co-owner alienate his share in the co-ownership? Yes, a co-owner may do so. Each co-owner shall have the full ownership of his part and of the fruits and benefits pertaining thereto, and he may therefore alienate, assign or mortgage it, and even substitute another person in its enjoyment, except when personal rights are involved. It must be noted, however, that he has no right to sell or alienate a concrete, specific, or determinate part of the thing in common to the exclusion of the other co-owners because his right over the thing is represented by an abstract or ideal portion without any physical adjudication; an individual co-owner cannot adjudicate to himself or claim title to any definite portion of the land or thing owned in common until its actual partition by agreement or judicial decree. What is the rule on partition of a co-owned property? No co-owner shall be obliged to remain in the co-ownership. Each co-owner may demand at any time the partition of the thing owned in common, insofar as his share is concerned, subject to certain exceptions under the law.  Article 484, Civil Code of the Philippines.  Art. 485, Civil Code.  Art. 491, Civil Code.  Cruz v. Catapang, G.R. No. 164110, February 12, 2008.  Art. 493, Civil Code.  Heirs of Jarque v. Jarque, G.R. No. 196733, November 21, 2018.  Art. 494, Civil Code.