The noun behalf (from Middle English, from by and half, meaning “side”) is an unusual word in a couple of respects.
For one thing, it is used only in two prepositional phrases, anchoring either “in behalf of” or “on behalf of.” Many other nouns are employed in similar prepositional phrases in which a pair of prepositions frame a noun, as in “in addition to” or “on account of,” but each of these nouns stands on its own, as do most others seen in prepositional phrases: “He’s designed an addition to his house”; “They opened a new account.” By contrast, behalf cannot stand on its own, without the support of prepositions, as in the nonsense sentence “He gave his behalf to their cause” (which tries, and fails, to independently employ the word in one of its senses, “support”).
The other anomaly is that behalf is associated with two possible preceding prepositions, when most prepositional phrases are restricted to one choice of prepositions. For example, in reference to the other phrases mentioned above, “in addition to” is not alternatively rendered “on addition to,” and “for account of” is not a variant of “on account of.” Similarly, many other prepositional phrases are also fixed. Here are some examples with some of the most common leading prepositions:
* against the advice of
* at the urging of
* by means of
* for fear of
* in case of
* on the merits of
* to the left of
* with respect to
Such prepositional phrases often have a stilted or even archaic feel to them. One other, which, like behalf, is based on a noun that cannot stand on its own, is “at the behest of” (which means “on the order of” or “at the request of”). Behest, which shares the Middle English prefix be- with behalf and means “command” or promise,” nevertheless cannot be used otherwise as a synonym for those words, as in the nonsense sentence “She behested that he leave immediately.”
By the way, what’s the difference between “in behalf of” and “on behalf of”? The distinction between the two is dissolving. In the former phrasing, behalf means “advantage,” “benefit,” or “interest,” and the phrase has the sense of helping someone, as in “We have donated equipment and supplies in behalf of the renovation.” “On behalf of,” by contrast, means “in place of” or “on the part of,” with the sense of representation, as in “On behalf of my partners, I accept this award for all of us.” “On behalf of” has largely supplanted the alternative phrase in both senses in British English, while in American English, the two phrases are used interchangeably. Less formally, for can replace either phrase, but if they are employed, the distinction between “in behalf of” or “on behalf of” should, at least in American English, be observed depending on the meaning.