create a cause of action in English law, though the other two can act in support of a cause of action or a reply to a defence. Under American jurisprudence, equitable estoppel is available only as a defence, while promissory estoppel can be used as the basis of a cause of action. The requirement of inducement and reliance are broadly the same for all reliance-based estoppels: (i) the representor must have intended (actual or presumed) the representee, or have been reasonably understood by the representee as having intended him, to act on the relevant representation (or promise), (ii) the form of reliance must have been reasonable or intended, and (iii) the representation must have caused the representee to act in such a way that it would be "unconscionable" for the representor to resile. Detriment is measured at the time when the promisor proposes to withdraw his promise, not at the time when the promise is made. Estoppel by representation of fact and promissory estoppel are mutually exclusive: the former is based on representation of existing fact (or of mixed fact and law), while the latter is based on a promise not to enforce some pre-existing right (i.e., an intention as to the future). Proprietary estoppel can operate only between parties who, at the time of representation, were in a pre-existing relationship, while this is not a pre-requisite under estoppel by representation of fact. English courts will consider unconscionability taking into account many factors, including the behaviour, state of mind, and circumstances of the parties. Generally, the following eight factors are determinative: how the promise/representation and reliance upon it were induced the content of the promise/representation relative knowledge of the parties parties' relative interest in the relevant activities in reliance nature and context of the parties' relationship parties' relative strength of position history of the parties' relationship steps, if any, taken by the promisor/representor to ensure he has not caused preventible harm. Estoppel by representation "Estoppel by representation of fact" is a term coined by George Spencer Bower. This species of estoppel is also referred to as "common law estoppel by representation" in Halsbury's Laws of England, vol 16(2), 2003 reissue. In at paragraph I.2.2, estoppel by representation of fact is defined as follows: A second definition can be found at at paragraph 9.02: A representation can be made by statement or conduct. Although the representation must be clear and unambiguous,