I know the expression 'on (someone's) behalf' usually reads or is understood as 'instead of someone' but I'm wondering if it's possible for it to have a benefactive reading, that is, if it can be used to express one has been benefited by somebody else's action. Can anyone help me?
At one time on behalf of and in behalf of meant different things:
on behalf of X meant “in X’s name”, “representing X”
in behalf of X meant “in X’s interest”, “for X’s benefit”
About 1800, however, on behalf of began to be used in both senses; and, no doubt in consequence, in behalf of started to fade from use a couple of generations later.
In 1887 the OED called this a “recent use” which it regarded as “the loss of an important distinction”; but the language marches on, callously indifferent to the pain of even her most devoted followers. Today you may use the phrase in either sense.