The burden of proof for contract content should be supplemented by the doctrine of distribution of burden of proof in the normative theory. The distinction between essential clauses and non-essential ones of a contract not only determines the scope of consensus required for the establishment of a contract, but also is decisive for the allocation of the burden of proof for both the establishment and the content of a contract. By deconstructing the single issue of contract law, the normative theory distinguishes between the consent and the content of contractual clauses and then further distinguishes the allocation of the burden of proof for the establishment and the content of a contract. According to the normative theory, the content of non-essential clauses should be proved by the claimant. If it is claimed by the plaintiff, the plaintiff should prove that it is the constitutive requirement of the contractual rights. If it is claimed by the defendant, the defendant should prove that it is a hindrance to the contractual rights. Since the non-essential clauses include naturalia and accidentialia, the claimant should prove the content of agreed naturalia that is different from the arbitrary norms. The claimant should prove the content of accidentialia, including the conditions or a time limit of a contract. In general, the content of essential clauses is proved by the plaintiff, that is, the plaintiff should prove the content of the clauses on the parties, the subject matter and the quantity. Price or remuneration clauses are divided into “should be paid” clause and “how to calculate” clause, the former is an essential clause, the content of which should be proved by the plaintiff, while the latter is a non-essential clause, the content of which should be proved by the claimant. In particular, the content of essential clauses is proved by the claimant when the right of agency is involved. |