Allowing science to consider how God is the life of the mental and natural worlds would be a big mental jump from any naturalistic starting point. It would necessarily change the kinds of scientific theories that should be permitted. We are thus going to introduce a new kind of science called theistic science, as suggested by Plantinga. You may argue that there is in fact only one kind of science, and that there is no sense in talking about e.g. `Australian science,' or `theistic science'. However, there are still ways in which plurality can and should be part of science. In particular, there can and should be multiple sources of ideas that lead to scientific theories. This means that we can consider theistic science as a branch of each theoretical science that derives general theoretical principles from the theism presented here, and begins to give the results described later in this book. In general, I argue that we should encourage `ontological pluralism'. This pluralism is already explicit in the foundation of physics, and in psychological modeling. Basic physics, for example, considers strings or spin foams or deformed space as alternative possible ontologies. Psychology can consider symbols or functions or network connections in alternative possible ontologies. There is no principle of science that forbids such ontological pluralisms.
Some may respond that this pluralism only makes sense in the initial stages of a science, but not in its mature stage. I reply that neither fundamental physics nor psychology are mature sciences in the required sense. Others may argue that we should stick with the framework we have, to see how far it will take us. There is always the possibility, they say, that materialist science may in the future give a complete and adequate account of mental processes, the creation of the universe, and of the creation of life, so in the meantime, we should not be impatient. To which I reply by asking us to consider the possibility that theism is true, and that God does make a difference to the world. Must we then wait 100 or 200 years until the naturalists have finally given up seeking natural explanations of those differences? Can we not start thinking now about these matters? To do so, is to encourage ontological pluralism in science, especially concerning foundational questions. As Feyerabend says in Against Method, in science there are in fact no fixed rules, and that successful explanation is what counts. If some of us want to seek alternate explanations in the chance that we may be more successful in producing scientific predictions, then we should be allowed to do so. This is pluralism.
We give the name of theistic science to the kind of scientific activity within ontological pluralism that develops theoretical ideas for the relation between God and the created world, and how they function together. This enterprise starts by rigorously formulating and examining a `scientific theism', and then leads towards theistic science that gives rise to `theistic psychology', `theistic biology', etc., within an environment of ontological pluralism. If successful, we might one day begin to call these just `science', but that, of course, remains to be seen.
Theistic science, therefore, simply starts with the postulate that there is a God, according to the living theism defined above. Just as naturalistic physics starts from the a-theistic assumption of God not existing (but something else), I start from the assumption of God existing. We have to assume that something exists, to start with, so both these ontological approaches should be allowed within science, as long as they produce good explanations. Science per se should not prejudge the kinds of ontologies to be assumed in the best theories, since that should depend only on the results of the investigations. The earth will not disappear from under our feet if we consider the possibility of God existing, to see what conclusions might follow from that assumption.