Both lien and pledge are predicated on possession of the subject matter. However, the thing to be retained is the subject matter of the main contract. For example, if you entrust me to process shoes and you fail to pay, I will have the right to retain the batch of shoes and exchange for them. The money is used to offset the payment you owe, but there must be a main contract, that is, an entrusted processing contract, and the shoes are the subject of the main contract.

The pledge also transfers possession, but the subject is not involved in the main contract. You must give me a certain amount in addition. In kind, money, or value certificates to guarantee performance. Once you fail to perform, I have the right to use these things to compensate for my losses

The mortgage does not transfer possession