On behalf of this fossilised phrase

We often refer to something being done on behalf of someone, but the word behalf appears only in this set phrase and variations on it. In other words it’s not linguistically productive, so it can be described as a fossil. But what is a behalf, and where does it come from?

On someone’s behalf, etymologically speaking, means ‘on someone’s side’, from an old meaning of half. It emerged in Middle English as a result of blending the two phrases on his halve and bihalve him, both of which meant ‘on [or by] his side’; thus Chaucer, ‘Spek thow thiself also to Troylus On my bihalve’. The word in modern use has two related meanings: 1. ‘instead of someone, or as a representative of someone’, and 2. ‘in order to help someone’. Sense 1 is more neutral, while sense 2 implies active support or defence of a person.

Macmillan’s American definition includes a variation with in as the preposition: in someone’s behalf, or in behalf of someone. Some usage commentators differentiate the in and on phrases semantically, restricting in behalf of to sense 2 above (‘in order to help someone’) and on behalf of to sense 1 (‘as a representative of someone’). But in practice the distinction is not generally made, and the two forms have always been used interchangeably – even by Shakespeare. Nowadays in behalf of is relatively infrequent in US English and seldom seen in UK English. Other versions using of, to and for in place of in/on failed to catch on.

Some weeks ago I was editing an academic text and encountered the modified form on their behalves. You can see the rationale for this plural: we say one half but two halves, one calf but many calves. But behalves is not the standard plural. Even when multiple parties are involved and someone is acting separately on behalf of each one, it’s still just on their behalf.

In his New Fowler’s Modern English Usage, Robert Burchfield notes a development where on someone’s behalf is used to mean on someone’s part, or similarly on behalf of is used to mean on the part of. He gives the example: ‘That was an 11th-hour decision on your behalf’, instead of ‘…on your part’. This is a once-obsolete usage being revived, but it is potentially confusing; in Burchfield’s example it could suggest that someone else made the decision. So on behalf of copy editors everywhere I recommend that you avoid it, at least in formal contexts.