In the recent joint statement by the British and Irish governments setting out their best guess on the bare bones of a settlement in Northern Ireland, there is a particularly important paragraph on human rights protection. It envisages provisions to safeguard the rights of both communities in Northern Ireland . . . "to achieve full respect for the principles of equity of treatment and freedom from discrimination, and the cultural identity and ethos of both communities."

The use of the term "equity of treatment" rather than "equality" has stimulated considerable debate, and no little alarm, since the publication of the joint paper. What, if anything, does this difference in language signify?

It is a cliche that choice of language is important in Northern Ireland; indeed, in the present situation of uncertainty surrounding the continued viability of the talks process, it could mean the difference between life and death.

But there is a considerable problem for those negotiating the choice of language: to whom is the language addressed, and for what purposes?

The problem arises because the language chosen must ultimately appeal to different institutional actors: it must immediately appeal to the politicians sitting around the table and those they represent.

The settlement must also be ratified by referendums. The public will be concerned at how their rights will be enhanced or undermined. They, too, must be convinced. And it is on the reactions of these groups and individuals to the choice of words that most attention is directed.

But the language agreed to in the talks process and in referendums will be put into some type of legal, and probably constitutional, form.

And this language will then be interpreted by civil servants, judges, and lawyers. Some may not like this but it is inevitable.

Sophisticated politicians and the voters should also gauge their reaction to the language of any settlement in part by how they think it will be interpreted by these lawyers and bureaucrats.

The words chosen, therefore, need to be seen as directed to the politicians, the electorate, and to those who will interpret that language. The words chosen must be explicit and be able to be made operational.

Nowhere, perhaps, is it more important to appreciate this point than in the human rights context. And a good illustration of how different groups may interpret a word differently is seen in the joint paper's use of the term "equity".

Part of the problem lies in the failure of the joint paper to disaggregate two overlapping, but distinguishable, equality agendas. One relates to equality between the two different sets of national allegiances, one Irish, the other British.

Much of the language of parity of esteem and equality of respect seeks to address this agenda. That language may or not be adequate, but my concerns lie elsewhere at the moment.

Another, different, agenda relates to equality between communities in Northern Ireland, defined by other characteristics: religion, ethnic affiliation, race, disability, gender, sexual orientation. I am primarily concerned with what language in any settlement best furthers this second equality agenda.

Equality between these groups is necessary in employment, but also well beyond that in all other areas of political and economic life as well. Measures to achieve that are necessary at the constitutional, legislative, and institutional levels.

Both equality agendas are vital to the creation of the type of society in which peace and reconciliation can grow, but the language necessary to reflect these concerns adequately in any agreed settlement may well be different.

For the second equality agenda, the use of "equity of treatment" is a real problem. It is seen by some as an attempt to weaken the equality agenda by deliberately choosing a weaker formulation than "equality". And this criticism seems to be given added weight by the fact that "equity" is classic Northern Ireland Office-speak. It is surprising that the language of equity was acceptable to the Government.

A response to this criticism may be that equality is too rigid and narrow a goal to aim for, that justice and fairness are the larger ideals on which Northern Ireland should be based in future, and that equity may well be more effective in capturing that ideal than equality.

I partially agree. There is a problem with the use of the term "equality". It could well be used, for example to rule out the type of affirmative action measures for disadvantaged groups that justice and fairness would encourage.

Here we come to the crux of the problem of interpretation. It is possible to interpret the language of equity in a broad way, encompassing ideas of substantive fairness and distributive justice.

But is it likely that this broad interpretation will be adopted by Northern Ireland civil servants and judges, following any settlement which embraced that formulation?

The evidence is that the justice/fairness interpretation is unlikely to be adopted in these contexts. My fear, based on past experience, is that a definition of equity would be adopted which concentrated on a much more conservative interpretation, one which emphasised stability, balance even in the face of injustice, the preservation of the status quo, not antagonising either side.

And that interpretation could cripple an agenda based on redistribution and fundamental change. While this may appeal to some in the talks, it risks perpetuating part of the problem that the peace process is meant to resolve.

My point is not that this conservative interpretation is the only legal approach to the meaning of equity. Rather, the problem is the very ambiguity of the term. As one legal commentator has put it: equity is a chameleon-hued word; hence it is advisable to pin down the particular meaning one attributes to it in a given context.

Of course, politicians will be politicians. Words will be used in negotiations that are intentionally ambiguous. Creative ambiguity is, and will continue to be, part of what oils the wheels of settlement. But in this context the ambiguity of equity is not creative, but potentially destructive. Its ambiguity is a luxury which can no longer be afforded.

So what should be done? First, there is a need to distinguish between the two different equality agendas, and appreciate that different language may be necessary to further these different agendas.

Second, sticking rigidly to equality may ultimately do more harm than good to the cause of justice and fairness between the different communities of Northern Ireland.

Third, language needs to be negotiated which unambiguously emphasises the need for substantive fairness, distributive justice, and participation rights as vital elements in any peace process.

Equity does not unambiguously and clearly achieve that. To adopt it as a central term in any settlement is storing up problems for the future.

Christopher McCrudden is reader in law, Oxford University and a Fellow of Lincoln College, Oxford. He was formerly a member of the Standing Advisory Commission on Human Rights.