The difference between property law and contract law is that property law mainly implements the principle of statutory property rights. Scholars have different explanations on why real right should be legal: some scholars believe that the reason why real right is legal lies in preventing the abuse of the principle of freedom of contract; Some people think that the statutory real right is to protect the security of transactions. These views are all reasonable, but I think the main reasons are: the property right has a strong exclusiveness, which can confront the third party (for example, the property right owner can exercise the right of recourse, but the creditor cannot pursue it from the third party), and the property right has priority (when the property right coexists with the creditor's right, it takes precedence over the creditor's right), so it is directly related to the interests of the third party, and the contract only occurs between the parties to the contract. The third party does not know that if the parties are allowed to create the property right only by perfecting the agreement of the parties, it will be inevitable. Not only does property right take precedence over creditor's rights, but creditor's rights with property right also take precedence over creditor's rights. Take mortgage as an example. Mortgage can only become real right if it is recognized by law. After the mortgage becomes the real right, the parties may not establish the mortgage through the contract. After the parties conclude a mortgage contract, they must register the mortgage before they can establish the mortgage right. If the parties conclude a mortgage contract, the mortgage will be established, and there is no legal provision, which is very troublesome. If I have a property worth 1 million and owe a lot of people money, I just want to give this 1 million to Zhang San, not to Li Si and Wang Wu, then I may sign a mortgage contract with Zhang San. If the property right can be created at will through the contract, and Zhang San enjoys the property right, he can be compensated in priority to other creditors, and others get nothing, then the transaction will be out of order. Mortgage is the burden of property, if it does not meet the prescribed conditions, it may lead to fraud. Legalization of real right is the basic principle of real right law in various countries.