English unjust enrichment law is part of the English law of obligations, alongside contract and tort, and property. A claim in unjust enrichment requires benefits that have been obtained by someone to be given up if it would be "unjust" to retain them. The enrichment must be "unjust" if no valid legal transaction is present, such as a contract, trust, gift or estoppel. "Restitution", or restoration of the unjust gain, to the party to whom the enrichment came from is the main right that follows from an unjust enrichment. English courts have recognised that to found a claim there are four steps: (1) someone has to be enriched, (2) at the expense of someone else, (3) the enrichment must be unjust, and (4) there must be no defence, such as the defendant changing its position on the strength of the enrichment. Around 10 major "unjust factors" are typically recognised in English law, many of which are typically understood in contract as "vitiating factors". If someone receives an enrichment at another's expense, and this is a mistake, it happens with the claimant's ignorance of the transfer, after a failure of consideration, under duress, under undue influence or exploitation, through legal compulsion, out of necessity, when the transaction is illegal, or the claimant lacks capacity or acts ultra vires, then this will found a claim, so long as no defence operates. Unjust enrichment is an action based on strict liability to return the enrichment, and may frequently work concurrently with a claim in tort. For example, if someone is forced to make a contract to transfer property, the "unjust factor" of duress will vitiate the contract. The claimant will be entitled to have their property returned, and will also have a claim in tort against the one who made the threat.