All writers who deal with the topic of mistake agree that there is great confusion of thought in discussions of the subject, but they attribute this confusion to different causes.1 The chief causes though frequently not recognized as such seem to be,

1. Confusion as to whether mental mutual assent or an expression of assent is an essential element in the formation of a contract;

2. Borrowing from the Civil law classification and rules which are not appropriate to English law; and

3. Failure to distinguish between an attempted contract entirely void because of mistake, and a contract which is merely voidable.

1 See 11 Columbia L. Rev. 197 (Roland R. Foulke).

The term mistake itself is moreover often used with two meanings. Story defines mistake as including some unintentional act, or omission, or error;2 and this definition is often repeated. Another learned writer says "the conception of a mistake involves in the first place the idea of action as a mistake can never be predicated of a state of mind." 3 In every-day speech mistake is doubtless used in two senses. When a man labors under a mistake his mental attitude is referred to, but it might also be said that one of his acts was a mistake. In legal phraseology, however, it seems that mistake is always merely a state of mind. Of course a state of mind produces no legal consequences unless some act capable of legal consequences takes place concurrently with the state of mind, and this is the only accurate meaning which can be attached to the statement often made that mistake as such has no legal effect; but what the effect of the act would be apart from the mental error, and whether this effect is changed because of that error, are two questions which must be separately considered. The subject of mistake properly includes only the second of these questions and involves the effect of erroneous ideas upon legal acts, or upon acts which would have been legal acts had it not been for the error.4 In this treatise the subject is necessarily confined to the effect of such erroneous ideas upon acts connected with the formation, performance or discharge of contracts.