In appropriate circumstances a court may conclude that by signing a document containing blanks a person should be regarded as having conferred implied authority on the other party to fill the blanks. That would apply in a case where the parties have reached express agreement upon the terms of a contract and one party signs it leaving in blank certain aspects. If the document is handed over to the other party in that condition it may readily be inferred that there is authority in the other party to fill in the blanks in accordance with the prior agreement.
Where there is no express agreement between the parties on a matter where the document remains blank at the time it is signed and handed over, it may still be proper to conclude that the party handing it over had impliedly authorised the other party to fill up the blank. In Wright v Gasweld this situation was considered :
“It may be, for example, that the information is unimportant, or that the common intention of the parties is such that the nature of the insertion is something which necessarily flows from that intention. I do not suggest that this account of the possibilities is exhaustive. Ultimately, however, the issue is one of fact, and the question is whether it is proper to infer that the party signing the document with the blanks in it gave the other party authority to fill in the blanks in the document.”
per Gleeson CJ.