The writer referred to in the preceding section has also stated as a requirement for the formation of contracts genuineness or reality of consent of the parties, and under this heading has included the subject of mistake, misapprehension, fraud, duress, and undue influence. But this supposed requirement for the formation of contracts is no real additional requirement to that of expressed mutual assent already stated. If there has been an expression of mutual assent, the fact that the expression was made under a mistake or induced by fraud, duress, or under undue influence, will not prevent the formation of a contract if there was assent, however induced, to make the expression in question.6 In some instances it is true there may seem at first sight to be an expression of mutual assent, and yet, in fact, be no such expression because the acts of apparent assent, when their real meaning is discovered,7 do not in truth indicate assent. In other cases because the assent has been induced improperly, the contract may be avoided by one of the parties to it, but it is of vital importance to distinguish between a voidable contract and an agreement which lacks altogether the essential requisites of a contract. Fraud, mistake and duress generally are personal or equitable defenses to a contract, and where they actually prevent the formation of a contract they do so because no proper expression of mutual assent existed-not because the assent was not "genuine." A contrary view is indeed common, and finds some warrant in the language of the cases, especially of decisions in equity, and text writers have drawn broad conclusions from such language. Thus in Ashburner's Principles of Equity,8 the learned author says: "If A. offers to sell Whiteacre to B for 1,000, and in his offer writes sell when he meant let, or Whiteacre when he meant Blackacre, or 1,000 when he meant 2,000, his mistake lies in a discrepancy between bis mental offer and his outward expression; and although B accepts in the bona fide belief that A meant what he had written, there is not in reality a concluded contract between the parties. If A is bound to carry out his written offer, he is bound not on the ground of contract, but on the ground of estoppel; and there seems no reason why he should be bound unless A has altered his position on the faith of the apparent offer." 9

3 See the following section. 4Sir William Anson, Principles of the English Law of Contracts. See also Holland, Jurisprudence (9th ed.), 252.

5 See infra, Sec. 1630.

6See infra, Sec.Sec. 94, 95, 1536-1537.

7 See infra, Sec. 601 et seq. as to what is the "real meaning" of the parties' expressions.

8P. 389.

9 The Even more extraordinary statement is made in 20 Amer. &. Eng. Encyc. of Law (2d ed.), page 809: "Courts of equity, in exercising the powers of rescission and reformation, do not operate upon contracts at all, but merely upon what erroneously provides conclusive proof of the mental attitude of the parties, the reply is obvious that to express the law in terms of conclusive presumptions is to express it in terms of fiction. If from A, B is always conclusively presumed, not B, but A is the essential factor.

In most instances it would make little practical difference whether it was said that the mental assent of the parties was the vital element in the formation of the contract, and that their words or acts proved their mental attitude, or whether it was said that their words and acts were the only essential matter in the formation of a contract. In some cases, however, the distinction is important. If it were true that the mental element was the vital matter the consequences would properly follow, as the writer just quoted suggests, that unless the other party has altered his position in reliance on the mistaken expression, there would be no obligation, and even if there were such alteration of position the obligation would be based on estoppel rather than on contract. There seems no trace of such a doctrine in courts of law, and such equity decisions as may afford some warrant for it may be explained as well or better on the theory that a contract exists but is voidable, as on the ground that no contract exists.10 Indeed if the view here criticised were sound there would have been little occasion for the exercise by courts of equity of a jurisdiction to rescind contracts for mistake. Wherever the difficulty is lack of such assent by one or both parties as is requisite for the formation of a contract, a court of law would be competent to treat the transaction as void. Yet equity took jurisdiction of the subject of mistake. Moreover, every term of an offer and acceptance is vital, and the two must be in complete accord. But a contract is not even voidable in equity because in some minor particular there was even a mutual mistake as to the meaning of the expressions used.

The parol evidence rule which is of such far reaching importance in determining the existence and meaning of contracts is based on the assumption that where a written memorial of the transaction is made its terms are conclusive. Such a rule is inconsistent with the view that the mental attitude or assent of the parties is the ultimate juridical fact to be established. If it be said that the parol evidence rule merely purport to be contracts." To say that a deed "erroneously purports" to be a contract or conveyance because the grantor was under an error in regard to the property covered by it is likely to lead to confusion and mistaken conclusions.

10 See infra, Sec. 1535 et seq.

Finally, the history of the common law is opposed to the view here criticised. The original basis of the action of assumpsit was consideration, and the essential feature of consideration was the justifiable reliance upon words or acts. The acceptor's justifiable reliance on the offeror's proposal is historically, and it is believed on proper analysis still law to-day, the basis of contract. The view here criticised was developed as part of the system of philosophy, law and economics, which, during the first half of the nineteenth century laid emphasis on the will. This philosophy has had great influence on the law of the continent of Europe and through the writings of Savigny especially, whose theories of the formation of contracts were made familiar to English and American readers by Sir Frederick Pollock, and others, has served to obscure the true foundation of the English law of contracts.