The term complementary to describe the relationship between science and religion is usually associated with Donald MacKay (1922 -1987). MacKay has been described by R. J. Berry as one 'who has probably contributed more than anyone this century to the Christian understanding of science '. One of the first uses of the term complementarity in this context was in a symposium on 'Mentality in machines', sponsored by the Mind Association and the Aristoltelian Society (1952).
MacKay later offered a more nuanced description of complementarity:
I call two or more statements complementary when (a) they purport to have a common reference, (b) they make different allegations, yet (c) all are justifiable in the sense that each expresses something about the common references which could not (for one reason or another) be expresses in the terms of the others - the commonest reason being ... that the terms belong to different logical categories.
Though the most common position held by evangelicals, it is not a uniquely evangelical or even Christian position. Brian Josephson , Plutarch (c. AD 45-120), a Baha'i, Khursheed, also belong to this category. An empirical study by Helmut Reich identified complementarity as the main approach to the interplay between science and faith by adolescents.
The complementarity position is often described as being analogous to different views of the same mountain, an architect's plan and elevation drawing, binocular vision, the wave-particle duality of electrons and light, and the hardware and software on computers. In the same way as electrons and light can be described by both waves and particles, so too can reality be explained by both religion and science without contradiction. Science and religion cannot be reduced to each other. They offer different, supplementary levels of explanation, which are true provided they are not contradictory, so the complementaritists argue
Complementarity despite its popularity is not without its problems. Polkinghorne notes that it is not an instantly explanatory concept. Ian Barbour is unsympathetic towards complementarity. He is dubious about extending the use of the term to explain science and religion. He is so for several reasons. It provides 'no justification for an uncritical acceptance of dichotomies'; it cannot be evoked to deal with inconsistencies. Models should be called complementary only if they 'refer to the same entity and are of the same logical type'; such as describing God as a Father and a Shepherd; or electrons as waves and particles, but not to two differing entities such as science and religion.
By describing two apparently contradictory events as complementary does not help in ascertaining the truth or validity of either of those events. In such a case complementarity is unhelpful. Can two incompatible events be described as complementary? For example, the Big Bang theory of origins and Genesis 1 may be viewed as complementary; but they could also be contradictory. Complementarity does not help in determining whether they are contradictory or not.
Complementarity also serves to divorce science from religion. This charge is denied by Bube. He notes (citing James Moreland ) that 'complementarity is compartmentalism' is a very common misinterpretation. And yet, the interaction that Bube insists that there is is very minimal: 'Complementarity recognizes that valid insights from science and theology both deal with the same reality and must be integrated', writes Bube, and yet he gives no indication of how it might be achieved in practice. This is why complementarity is placed within a soft independence position in my categorisation. Complementarists tend to deny independence in theory but acts as if religion and science were largely independent in practice. Professing complementarists, but practising independentists? One means of support for a complementarist position, proposed by Van Till, is to say that there is a 'functional integrity' within creation. Van Till draws upon Augustine and Basil and yet he is guilty of eisegesis in that he reads them in the light of his complementarist perspective - and of a very selective reading of Augustine, in particular.
Adherents of complementarity tend to use the Baconian metaphor of the two books: the book of scripture and the book of nature. This metaphor was probably first used by Francis Bacon in his The Advancement of Learning and the New Atlantis (1605; sections 1.1.3, 1.6,16) It was adopted by
...those who inclined towards developing the idea of neutrality, or separateness, or autonomy, of science took a position that became epitomized in the metaphor of the two books, the Book of Scripture and the Book of Nature, both created by God as manifestations of His omnipotence and omniscience, but books different in character that had to be kept apart.
Complementarity largely accepts that science is neutral in regard to religious belief. This is certainly the position of MacKay in practice if not in theory:
The discipline of science is autonomous in the sense that we need not have any explicit theological convictions in order to practise it. It has developed and been moulded under pressure of the data themselves - data to whose implications Christian and non-Christian alike find they must be obedient if their scientific enterprise is to succeed.
If the scientist is also a Christian, there is no implication that he should necessarily do better in science, still less that his scientific findings should differ from those of his non-Christian colleagues.
Here is a denial that Christianity has anything to do with science, and an endorsement of methodological naturalism. For MacKay science is divorced from any religious or cultural presuppositions; this is dangerously close to a positivist view of science: a science that must bow down to bare value-free facts. Science, for MacKay, is neutral with respect to religion and faith commitments.
The scientist's reasons for keeping his private emotions [and presumably religious commitments] out of the official picture is that, despite his enthusiasm for the subject, he would like to be able to be able to describe the world as it is - as it would be without him.
He also writes of 'the neutral character of scientific chance' and of a 'theologically neutral, scientific notion'. It appears that faith is the 'icing on the cake'; an additional extra, rather than an important essential to science:
As a scientist, I have the job of helping to build scientific language - at the scientific level - as a complete a description of the pattern of physical events as I can, regarding no accessible events as exempt from examination. As a Christian, I find that the very same pattern of events can bear an additional and vital significance as part of the activity of God himself.
This position is, I believe, unsound, no matter how attractive the complementary position is. We do well to recall the advice given to Archbishop William Temple by his tutor: a phrase is not a solution. It implies that religion has nothing to do with science: Do Christian commitments count for nothing when one does science? Complementarity enables MacKay to adopt a mechanistic approach to his science:
... my own research department at Keele is concerned with the mechanisms of the brain, and that our working hypothesis is that the brain is capable of being studied as a mechanistic system.
Viewing humans as mechanisms may be complementary to a Christian perspective, but is it a biblical option? Are complementarists content to leave their religious beliefs at the laboratory door? Complementarists thus endorse methodological naturalism.
To be fair to MacKay he recognizes that complementarity 'is not a universal panacea ... A good deal of consecrated hard work is needed on the part of Christians to develop a more coherent and more biblical picture between the two'.
At worst complementarity is a convenient label under which one can avoid compromising religious beliefs by accepting the secularisation of science. The term complementarity is best left to describe wave-particle duality or even mind-matter and free will-determinism, but not science and religion. Religious beliefs are much more integral to science than complementarity suggests.
(Taken from my paper 'A typology of science and religion' Evangelical Quarterly 2000)