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Does Mathematics Need a Worldview?
(Paper presented at the "Man & The Christian Worldview" Symposium, Alushta, Ukraine, May 16, 2008)
John Byl, Ph.D.
It is widely thought that mathematics is strictly rational, that it needs no beliefs, and that it strongly supports naturalism. Yet, in actuality, one's view of mathematics and, hence, what one considers to be valid mathematics, depend heavily on one's worldview. The educational institutions of a free and just society should therefore pay more attention to how presuppositions from various worldviews impact mathematics. In this paper we shall examine, in particular, the implications of naturalism and theism for mathematics.
A fundamental question: Is mathematics discovered or invented? Most mathematicians believe that they are discovering properties of, say, prime numbers, rather than merely inventing them. They believe that mathematical truths exist independently of human minds, being universally and eternally true.. This view of mathematics dates back to Pythagoras (ca 569-475 BC) and Plato (427-347 BC). It is often called mathematical "realism". The early Christian philosophers Augustine (354-430 AD) placed the ideal world of eternal truths in the mind of God. Augustine argued that mathematics implied the existence of an eternal, necessary, infinite Mind in which all necessary truths exist. Thus arose the classical Christian view that mathematics exists in the mind of God, that God created the universe according to a rational plan, and that man's creation in the image of God entailed that man could discern the mathematical patterns that God has placed in creation. Mathematics was held to be true because it was upheld by God. This notion of a rational Creator was a major factor in motivating the scientific revolution. Kepler, Galileo, Newton, and many other founders of science were driven by their Christian worldview.
2. Materialism and mathematics
Currently, naturalism has replaced Christianity as the predominant worldview operating in the science. Most naturalists are materialists, believing that everything--even consciousness and mind--is just a form of matter. Materialists believe that mathematical objects exist only materially, as physical states of our brains. Stanislas Dehaene (1997) postulates that evolution hard-wired the smallest integers (1, 2, 3...) into our human nervous system, along with a crude ability to add and subtract. Materialist explanations seek to explain all our mathematical concepts in terms of purely physical connections between neurons.
Such a materialist account of mathematics raises some problems:
(1) Such proposals for simple arithmetic are entirely hypothetical. No actual mathematical mechanisms have as yet been found in the brain. Further, it is hard to see where more advanced mathematics comes from, since our capacity for advanced mathematics seems much greater than needed for mere survival skills.
(2) Moreover, if our mathematical ideas are just the result of the physics of neural connections, why should they be true? Where do logical norms enter into our thinking? Such accounts of mathematics cannot distinguish true results from false ones. Nor can they yield any explanation for correctness, a basic issue in mathematics.
(3) Central to mathematics are the notions of truth and logic. A belief is true only if it corresponds with what is actually the case. Knowledge about reality involves our capacity to represent some aspect of reality as a thought in our mind. Our beliefs are judged to be either true or false depending on how well they represent reality. However, truth and falsity are objective properties of our representations, not of the external world itself. Physical objects do not, in themselves, represent anything beyond themselves. They can be interpreted by us as representing something other than themselves, but the actual representation is then our mental interpretation. No physical property or combination of properties can constitute a representation of anything. Hence truth cannot be reduced to a physical property. Thus truth cannot be explained by materialism.
Closely related to truth is logic. Logical propositions are either true or false. Logical laws and relations connect the truth-values of different propositions. Since truth is not a physical property, neither is logic. Moreover, logical laws, unlike laws of physical or psychological fact, are neither hypothetical nor inductive. Rather, they are necessary and universal, remaining valid regardless of the state of the physical world. Logical laws, like truth, are abstractions and belong to the realm of ideas, not matter. But consistent materialistic naturalism must reject abstract objects of any kind (including sets, numbers, propositions, and properties), if we take these in the traditional sense of being non-physical.
Most mathematicians believe that numbers, equations, perfect circles, and so on, exist in some ideal, abstract sense. Such non-physical objects must be rejected by consistent materialists. But if ideal entities do not exist, this means that any propositions concerning them cannot be true in the sense of corresponding to anything. One is then forced to either reduce mathematics to a mere game with meaningless symbols or to think of mathematical objects as part of the physical world, which is clearly not the case. Consequently, few mathematicians are materialists.
(4) If materialism has no place for ideal entities, then it must deny also the existence of universal norms. This affects not just mathematics but rationality in general. Rationality presumes the existence of objective, rational "oughts" that prescribe how we are to reason. Given certain arguments and evidence, a rational person ought to accept the conclusions they entail. This implies the existence of objective laws of logic and rules of evidence. Since materialism has no place for non-physical, universal norms, it can have no absolute standards of right or wrong mathematics. Hence, it must postulate that all norms--whether rational, mathematical, or moral--are purely human inventions. Truth and falsity, right and wrong, and good and evil are thus reduced to mere human opinion or convention.
The above considerations have implications also for the content of mathematics. Classical mathematics is based on the concept of an Ideal Mathematician. It assumes the existence of an all-knowing, all-powerful and infinite God. The operations and proofs allowed in classical mathematics are those that could in principle be performed by such a God.
If, on the other hand, mathematics is merely the creation of the human mind, then its methods should be adjusted accordingly. Consequently, many naturalists believe that one should consider as valid only those mathematical concepts and proofs that can be humanly constructed in a finite number of explicit steps. The constructionist mathematician Errett Bishop writes,
"Mathematics belongs to man, not to God. We are not interested in properties of the positive integers that have no descriptive meaning for finite man. When a man proves a positive integer to exist, he should show how to find it. If God has mathematics of his own that needs to be done, let him do it himself". (Bishop 1967: 2)
Bishop urged that classical mathematics be replaced with constructive mathematics. This restricts the logical law of excluded middle, proofs by contradiction and actual infinite sets. As a result, constructivists reject many theorems of classical mathematics. Unfortunately, some of these classical results are essential for modern physics, which relies heavily on advanced mathematical concepts that are beyond the current range of constructive mathematics. In short, the mathematics needed for science is the classical mathematics based on the Ideal Mathematician of theism.
4. The Indispensability of Mathematics for Science
This brings us to a deeper problem. Mathematics is indispensable to physics, which is essential to materialism. Willard Quine (1981: 14-15) argues that, since we ought to be ontologically committed to those entities that are essential to our best scientific theories, the indispensability of mathematics to science gives us good grounds to believe in the objective existence of mathematical entities, such as sets and functions. If a scientific theory is confirmed by empirical data, then the whole theory is confirmed, including whatever mathematics the theory uses. Since science deals with real objects, it would seem that mathematics must also deal with real objects. This applies even more so for those embracing a realist view of scientific theories. How can scientific theories be true unless the underlying mathematics is also true? A recent defense of mathematical realism based on the indispensability argument is given by Mark Colyvan (2001).
The amazing success of physics, due largely to its mathematical nature, counts strongly against the notion that mathematics is merely a human invention. It suggests that the physical world has an objective mathematical structure. Mark Steiner (1998) finds that the applicability of mathematics concerns not just a few isolated successes in physics. Rather, our entire universe seems to be mathematically "user friendly" to humans.
Further evidence for realism is the universality of mathematics. Mathematicians widely separated in space, time, and culture find the same mathematical theorems. Realism is further bolstered by the strong sense of discovery mathematicians have when finding new theorems, by mathematical intuition, and by the fact that realism is the working philosophy of most mathematicians. In the last century realism has been explicitly defended by a number of outstanding mathematicians, including Georg Cantor, Kurt Gödel, G.H. Hardy, and Roger Penrose.
5. Realism and Theism
The main difficulties associated with realism are (1) where to place the ideal world of mathematical entities and (2) how this ideal world interacts with matter and human minds.
Paul Benacerraf (1983: 412) contends that true beliefs constitute genuine knowledge only if their truth is causally responsible for our belief. How can mathematical entities, which are causally inert, give rise to our mathematical knowledge? How can they can be responsible for the world's being the way it is? Realism requires an active agent. In the Christian worldview mathematical objects are causally effective in the world and in our minds by virtue of being in the mind of God. God makes the required connections. David Griffin comments:
"The implication of Benacerraf's insight...is that atheism renders unintelligible the idea that we can have knowledge of a Platonic realm of numbers…As Quine points out, however, such a realm is presupposed by physics. Benacerraf's insight, plus Quine's observation, implies that atheism makes an adequate philosophy of mathematics impossible." (Griffin 2002: 373)
Once theism is dropped, it is difficult for realism to explain where objective mathematical truths exist and how we have access to them. Mathematical realism is plausible, it seems, only within a theistic worldview.
Mathematics fits well within a Christian worldview because the biblical God has a logical aspect ("the spirit of truth" John 15:26) as well as a numerical aspect (the tri-une God of Father, Son and Holy Spirit). Since God is eternal, so are logic and number. God is also infinite, omnipotent and omniscient; His knowledge encompasses all events, thoughts and possibilities, including all possible mathematical propositions. God's upholds all truths, including truths about mathematics. Hence a mathematical entity need not be explicitly constructed in order to exist. Since God has created the world according to a rational plan, the world may be expected to exhibit mathematical structure. Since God has created man in God's image, which includes rationality, humans may be expected to discern this mathematical structure.
Virtually all of contemporary mathematics can be derived from modern set theory. It is noteworthy that Georg Cantor (1845-1918), the founder of modern set theory, justified his belief in infinite sets by his belief in an infinite God (see Dauben 1979:229). He thought of sets in terms of what God could do with them. Even today, almost every attempt to motivate the principles of set theory relies on some notion of idealized manipulative capacities of the Ideal Mathematician.
In summary, one's worldview does make a difference in mathematics. Naturalism, which takes mathematics to be a mere human invention, raises questions about the truth and validity of mathematics. Materialism has no place for mathematical entities, universals, or even truth. A purely human, constructive mathematics does not yield sufficient tools for modern physics. The indispensability of mathematics for physics is a strong argument for realism. However, since mathematical entities are causally inert, realism must be supplemented with an active agent that can connect mathematics to matter and mind. Thus mathematical realism requires a theistic worldview. Further, both classical mathematics and modern set theory presume the existence of an Ideal Mathematician--an all-powerful, all-knowing and infinite God.
Given the significant role that worldview plays in mathematics, a just society should allow freedom for professors to explore the implication of various worldviews for mathematics. In particular, naturalism should not be dogmatically and uncritically imposed. Room should be given for alternative views, such as theism. This is particular so since mathematics is more readily accounted for and justified by theism than it is by naturalism.
Benacerraf, Paul 1983. "Mathematical Truth" in Paul Benacerraf & Hilary Putnam (eds.) Philosophy of Mathematics (2nd ed.). Cambridge: Cambridge University Press.
Bishop, Errett 1967. Foundations of Constructive Analysis. New York: McGraw-Hill.
Colyvan, Mark. 2001. The Indispensability of Mathematics. New York: Oxford University Press.
Dauben, Joseph W. 1979. Georg Cantor: His Mathematics and Philosophy of the Infinite. Princeton, NJ: Princeton University Press.
Dehaene, Stanislas 1997. The Number Sense: How the Mind Creates Mathematics. Oxford: Oxford University Press.
Griffin, David R. 2002. "Naturalism: Scientific and Religious", Zygon 37 (No.2): 361-380.
Quine, Willard V.O. 1981. Theories and Things. Cambridge: Harvard University Press.
Steiner, Mark. 1998. The Applicability of Mathematics as a Philosophical Problem. Cambridge, MA: Harvard University Press.