Atribución voluntaria de ganancialidad vs. prueba de la privatividad de los bienes: ámbito y efectos. comentario a la STS de España núm. 295/2019, de 27 de mayo
The mechanism of voluntary attribution of common nature to property does not proceed unilaterally (i.e., by the only will of one of the spouses), but only operates by mutual agreement between spouses. When a spouse acquires a property alone and declares to do so in favour of the community of property, this manifestation is not sufficient to attribute the status of common property to the acquired property. So, if this spouse proves that acquired the property with personal money, the property acquired will also be personal. The situation is different when both spouses acquire a personal property and agree to attribute common nature to that property. In this case, even if one of the spouses proves that the money invested to acquire the property was personal, the property will not be personal. However, the spouse who contributed with privative money may require repayment of the money used, even if it has not made a reservation regarding the source of the money or regarding its right to reimbursement during the acquisition
