There a tactic that relies on this rule and that is useful when confronted with a counter-party who won’t negotiate away an ambiguous statement. Simply send an email to them confirming that the such-and-such clause means X, not Y, then print their answer confirming that fact and file it with your copy of the contract. It’s almost as good as changing the words in the document, but most people won’t think twice about the email.

Chris Lemens

My only caveat is that if your client is aware of the ambiguity and the potential consequences, then they are free to take that risk – it may be a very small one. I would never advise a client to take that route though, because the “positive” result still involves litigation. I don’t think they would be impressed by my professional standards if I suggested it, either.

Also, does anyone have any views about whether the doctrine of mistake would apply to this kind of scenario (assuming it applies in the US as it does in the UK)? It would seem generally relevant, but perhaps it does not apply if there is a contract that can be interpreted objectively?