Confirmation of Verbal Instruction (CVI)
A written record, sent by the contractor, confirming an instruction that was given verbally — and stating that the work will proceed on that basis unless the recipient objects within a stated period. It converts a conversation into a document.
The mechanism relies on silence. The CVI says: you told me to do this, I am doing it, and if that is not what you meant you have seven days to say so. If nothing comes back, the instruction is on the record and the contractor has the paper it needs.
The reason it works is that objecting is easy and remaining silent is easy, but retrospectively denying an instruction you were told about in writing and did not dispute is very hard. Which is precisely why the CVI must go out promptly — a CVI raised three months later, when the work is already built, has lost the property that made it useful.