However, at common law this was a criminal offence (going by the contradictory sounding name of uttering a false document) and in most English law based legal systems it is still an offence today, although in many cases statutory provisions have superseded the common law (for example, in the British Virgin Islands see section 242 of the Criminal Code 1997).
It’s not unusual for parties to a contract to want the written agreement to cover a period before it’s actually signed.
My father (who was also a lawyer) used to love telling a story about how he was able to triumphantly prove to the court that a yacht charter was back dated by showing the stamps which had been used to pay the nominal 15¢ stamp duty were in fact first issued by the post office some four months after the date stated on the face of the document.
Effect of backdating a contract
There are any number of contexts where this comes up — some legitimate and others not exactly aboveboard — but the logistics of negotiating and signing contracts are such that the issue is unavoidable.
(Jason Mark Anderman illustrates the logistics problem well in this comment to a backdating post on Ken Adams’s blog.) There’s nothing inherently illegal or unethical about backdating contracts, although backdating can certainly be both unethical and illegal, depending on the situation.
Furthermore, giving the written contract its own date simply reflects the reality of how the contract process unfolded, and it’s always good to have contracts track reality.
If the date of the oral agreement was reached is somehow significant, then mention it in the recitals of the written contract.
When we say “back dating” what we usually mean is executing a document and then dating it with an earlier date than the actual date of execution, with the intention that it should be treated as giving rise to legal rights before the actual date.