Short answer. Co-ownership rules apply. Article 1775 of the Civil Code says associations and societies whose articles are kept secret among members, where any member may contract in his own name with third persons, have no juridical personality and shall be governed by the provisions relating to co-ownership rather than the general rules on partnership.
What the law says
Associations and societies, whose articles are kept secret among the members, and wherein any one of the members may contract in his own name with third persons, shall have no juridical personality, and shall be governed by the provisions relating to co-ownership.
Civil Code, Article 1775 — Secret Associations. Read the full provision →
What makes an association fall under Article 1775
Article 1775 describes a specific combination of facts, not secrecy alone. Associations and societies, whose articles are kept secret among the members, and wherein any one of the members may contract in his own name with third persons, shall have no juridical personality, and shall be governed by the provisions relating to co-ownership. Two things have to be true together: the governing articles are kept secret among the members, and any member is free to contract with outsiders in his own name rather than in the association's name.
Why secrecy costs the association its juridical personality
An ordinary partnership is generally recognized as having a personality separate from its individual partners, which lets it hold rights and obligations as an entity. Article 1775 withholds that status here because the association's own articles are hidden from outsiders and members deal with third persons in their own names — there is no outward-facing entity for third parties to recognize as a distinct partner in the transaction, only individual members acting for themselves.
What 'governed by the provisions relating to co-ownership' means
Instead of partnership rules, Article 1775 routes the arrangement into the Civil Code's provisions on co-ownership. That reframes how the members' relationship to whatever property or interests they hold together is treated in law: as co-owners sharing an undivided interest, rather than as partners in an entity separate from themselves. The internal secrecy that disqualifies the arrangement from partnership status is precisely what pushes it into this different legal framework.
What this means for members of a secret association
If your arrangement fits Article 1775's description — secret articles among members, and members free to contract with third persons in their own names — you should not expect the protections or structures that come with recognized partnership status, such as a separate juridical personality standing apart from the individual members. Your rights and obligations toward each other, and toward whatever you hold together, are instead worked out under the rules that govern co-ownership.