Last week a new campaign was launched in the Church of England to 'enable same-gender couples to be married in Church of England parishes.' The name of this campaign is 'Equal' and it describes itself as 'The campaign for equal marriage in the Church of England'.

The use of the term 'equal marriage' by this campaign is not a novelty. It is in fact merely echoing the language used by those who successfully campaigned for the introduction of civil same-sex marriage in England, Wales and Scotland and who are currently campaigning for its introduction in Northern Ireland.

The use of the term 'equal marriage' by both secular and religious campaigners for same-sex marriage reflects the force that arguments based on the principle of equality have in British society and across the Western world as a whole. The implicit argument evoked by the use of the word 'equal' by campaigners for same-sex marriage runs as follows:

- Major premise – the principle of equality, enshrined in British law by the Equality Act of 2010, is a basic moral principle which all right thinking people should accept;

- Minor premise – same-sex marriage is an example of equality;

- Conclusion – same-sex marriage should be accepted by all right thinking people (including those in the Church of England).

This argument undermines itself because the very principle of equality to which it appeals leads to the conclusion that same-sex marriage should not be accepted.

As American writer John Safranek explains, in order to decide whether two situations are in fact equal one has to have a common standard of measurement against which to assess them:

"Equality consists of a triadic relationship. To compare two things as equal or unequal, one needs two objects that can be compared and a standard by which to compare them; to speak of equality in isolation from a common standard is meaningless. Is a paraplegic Caucasian male equal to a Hispanic female track star? The question is unanswerable because, although two objects are being compared, some standard must be offered to compare them.

"The question of equality cannot be answered until the standard of comparison is stipulated. They are unequal in weight, sex, skin colour, mobility, ability to bear children, and numerous other qualities, but they are equal in being mammalian, human, alive, rational, desirous, and possessing five senses. These two individuals are equal to a census taker, since each counts as one citizen, but unequal to a track coach. Is an acre of land in Paris equal to an acre of land in Detroit? It all depends on whether the metric is area, financial worth, or soil quality.

"Whether the two are equal depends on the relevant standard, and the relevant standard does not depend on equality, but on other criteria considered important to the one comparing. Once the standard or metric has been established, then equality can be determined." (John Safranek, The Myth of Liberalism, Washington DC: The Catholic University of America Press, 2015, pp.51-52)

The appropriate standard for assessing same-sex marriage

The claim that is made by those campaigning for the Church of England to permit same-sex marriages is that marriages between two people of the same sex are equal to marriages between two people of the opposite sex. Hence the principle of treating equal things equally means that the Church of England should permit both.

However, as we have just noted, in order to determine whether these two types of marriage are in fact "relevantly equal" we have to have a common standard against which to compare them. Since the Church of England holds that marriage was established by God ("instituted by God in the time of man's innocency" as the Book of Common Prayer puts it) it follows that the common standard has to be the form of marriage which God established.

We learn what form of marriage God established from the creation accounts in Genesis 1 and 2 and from Jesus' teaching about marriage in Matthew 19:2-6 and Mark 10:2-9 which refers back to these creation accounts.

What we learn from these sources is that God established marriage as a permanent and exclusive sexual ('one flesh') relationship between one man and one woman which is in principle open to the procreation of children as a fruit of that relationship.

When judged by this metric, same-sex marriages fall short in two basic respects. They are not a sexual relationship between a man and a woman and they are intrinsically closed to procreation. It follows that they do not conform to the form of marriage established by God and that they are therefore not equal to the traditional, opposite sex, form of marriage currently permitted by the Church of England, since this does.

Why same-sex marriages should not be accepted

What this means is that the appeal to equality in support of same-sex marriage being permitted by the Church of England undermines itself. Same-sex marriage is not equal to the form of marriage established by God which the Church of England celebrates. Therefore it should not be treated as if it was, because just as the principle of equality says equal things should be treated equally so also unequal things should not be treated as if they were.

If same-sex marriages are not a form of marriage established by God then what are they? The answer is that they are what the New Testament calls por-neia, extra-marital forms of sexual activity that are contrary to God's will and in which God's human creatures should therefore not engage. (For justification for this point see Martin Davie, 'Glorify God in your Body' (London: CEEC, 2019), ch.8.)

Dr Martin Davie is a theological consultant for the Church of England Evangelical Council and the Oxford Centre for Religion in Public Life and is Associate Tutor in Doctrine at Wycliffe Hall, Oxford. He was formerly Secretary to the Faith and Order Commission of the Church of England and theological consultant to its House of Bishops.  The full version of this article first appeared on his blog, Reflections of an Anglican Theologian.