The deep transformations experienced by personal credit guarantees seem to call into question its link to the main contract which, in the Western legal tradition has always been considered its ultimate foundation. The aforementioned crisis of the link between the guarantee and the main contract gives us a great opportunity to shed light on its present role, its efficacy, as well as its limits and exceptions. This paper puts forward a unitarian understanding of personal credit gurarantees, on the basis of the principle that guarantees are linked to the main contract. Only a correct understanding of the way the link between guarantee and the main contract works enables us to redefine correctly, from a completely new and original perspective, other key concepts of contract law, such as joint liability, novation and payment by a third party.