§ 169. in behalf of / on behalf of
A traditional rule holds that in behalf of and on behalf of have distinct meanings. Accordingly, you should use in behalf of to mean “for the benefit of,” as in We raised money in behalf of the earthquake victims. And you should use on behalf of to mean “as the agent of, on the part of,” as in The guardian signed the contract on behalf of the child. But as the two meanings are quite close, the phrases are often used interchangeably, even by reputable writers.