Why is it sometimes necessary to obtain the intervention to a deed of sale of a married spouse or a civil union spouse who is not the owner?

The notary who receives a deed of sale must guarantee to the purchaser a clear title, or in other words, free of rights. This approach is important because it allows to ensure the purchaser that no other person can allege to have rights on the real estate property. We are thinking here of the rights that previous owners, or their spouses, could have kept.