What is the counter-argument against establishing a pledge before the debt is established?

Primary text

The objection against a pledge preceding the debt is that it is a security for a right that is not yet obligatory, thus it cannot be validly established beforehand, similar to testimony (Shahadah). Moreover, the pledge is secondary to the right and cannot precede it, just as the price cannot precede the sale. While a guarantee might be permissible, a distinction exists: a guarantee is an undertaking of liability freely given by word and is valid without an existing right, like a vow (Nadhr), unlike the pledge.