TM05: 6 July 2003
Copyright © 2003 by Kevin Sharpe. All rights reserved.
Submitted for publication.

 

 

Theology Can Use the Scientific Method

and Still be Theology

 

by

 

Kevin Sharpe

Graduate College, Union Institute and University, Cincinnati, USA;
Harris Manchester College, Oxford University, Oxford, UK;
Oxford Institute for Science and Spirit, Oxford, UK;
Founder,
Science & Spirit Magazine.
10 Shirelake Close, Oxford, OX1 1SN, United Kingdom.
kevin.sharpe@tui.edu
www.ksharpe.com

and

Jonathan Walgate

Physics Department, Oxford University, Oxford, UK
jon.walgate@qubit.org

 

 

 

 


ABSTRACT.

To compare the methods of science and theology, and explore the application of scienceís to theology, we first outline the scientific method as it has evolved from sociologically oriented philosophers and historians of science. Second, we look at what the method might mean for the structure of a theology and, third, we pursue outcomes and implications of the move, especially over the scientific nature of theological language and the truth of theological statements. An empirical method for theology assumes the existence of God and then asks what Godís nature is. It uses scientific techniques on proposed answers.

KEY WORDS.

God-world relationship, nature of God, philosophy of religion, philosophy of science, scientific method, theological method.

CONTENTS.

The Scientific Method. 1

In Defense of Reason. 1

Scientific Theology. 1

Differences between Scientific and Theological Criteria and Methods. 1

Science and Theology. 1

References. 1

Notes. 1


Isaac Newton, perhaps Englandís finest physicist, considered only two things worth studying: the work of God and the word of God. The usual image of theology conjures up pictures of the study and preservation of accepted doctrines, yet not long ago it lay at the cutting edge of discovery.

Science alone in the publicís eye now holds this lofty position as the vanguard of human knowledge. So powerful is its image that Richard Dawkins introduces his book, The Selfish Gene, with G. G. Simpsonís claim that evolutionary science renders meaningless all other attempts to answer the questions, ĎWhy are we here?í and ĎWhat is our purpose?í[1] This is false; theological language has meaning for people and valuable things to say. But theological language must adapt to the times in a world that increasingly looks to scientific proof for its criterion of truth. This paper accepts the challenge.

We suggest that theological language describes reality as does scientific language. We also suggest that the idea ĎGodí has a referent that functions at a metaphysical level just as the idea Ďobjective realityí functions in physical science. Theology, therefore, can and should follow a method analogous to scienceís.

The paper follows a straightforward plan. We seek to apply the method of the sciences to theology, and so, as a first step, we outline that method, especially as it develops from the sociologically oriented philosophers and historians of science. We attempt to justify its application to theology and look at the outcomes and implications of the move, especially at the scientific nature of theological language and the truth of theological statements.

We hope this stand, though it reflects an empirical bent and affirms theologyís scientific nature, will contribute to an awareness and understanding of the primary decisions for any theology.

The Scientific Method

Science is a useful, productive, and successful endeavor. The evidence is all around us − planes in the sky, computers in our laps, and vaccines in our bloodstream. The publicís faith in the accuracy of science is greater than at any time in history. Science is truth. But all is not well with the unqualified acceptance of this Ďgospel truth.í

The logical positivist movement had built up an unrealistically mechanical model of scientific practice, a model that simply did not fit. The attack began in the 1950s. Thomas Kuhn exposed and dispelled the central myths of the Ďscience is truthí position: namely, that all data are independent of theory, that theories are verified or falsified from these data, and that the resulting choice between theories is entirely rational and objective. In his book, The Structure of Scientific Revolutions, Kuhn went further, and portrayed science as irrational and subjective; it even became unclear how science achieved any results at all.[2]

These opposing interpretations now converge into a realistic appreciation of scientific study.

Ian Barbour describes scientific practice in his book, Myths, Models, and Paradigms.[3] A scientific discipline comprises research traditions, he writes, one such tradition often dominating a discipline. Key examples (or paradigms) embody each tradition and, as the subjects of teaching and modelling, initiate a student into the accepted methods for attacking problems. The paradigms also guide the traditionís research programs.

A research tradition also assumes, sometimes jointly with other research traditions, certain metaphysical beliefs. They assume what sorts of things exist in the world, what qualities of experience are the most fundamental, and so on. Newtonian mechanics (once an extremely powerful paradigm and still reigning in some disciplines such as biochemistry and psychology) generated a widely accepted collection of metaphysical commitments concerning the regularity, causality, and action-at-a-distance properties of the universe. Newton was troubled by his theory of gravity because he disliked its crucial assumption that bodies separated by vast distances, and with no visible connection, can nevertheless exert forces upon each other. The debate still rages: is action-at-a-distance desirable? The question lies in metaphysics because it concerns how theories should work rather than how the world does work. Such principles represent bedrock for science, but observation need not directly root them. They are assumptions about the patterns that observations fit into.

The doing of science within a research tradition requires the construction of models and theories. A model is an imagined mental construct, usually a mechanism or process. The scientist formulates an analogy between the patterns of a phenomenon and an imaginary construct, and a theory develops that matches observable aspects of the phenomenon with terms of the model. A familiar and intelligible situation thus becomes, with creative imagination, the basis for understanding some other aspect or part of the world.

Theories must be worthwhile. Criteria, which include simplicity, coherence, and agreement with experimental evidence, assess their value.

        ĎSimplicityí refers, not only to simplicity in the form of the theory and the minimum number of independent assumptions, but also to an aesthetic element: the beauty, elegance, and symmetry of the theory.

        ĎCoherenceí refers to a unification of separate laws, a systematic linking of theories, and exposing similarities between diverse phenomena.

        ĎSupporting experimental observationsí refers to a theoryís accurate account of known observations and prediction of future measurements, especially fresh discoveries. This is the main criterion.

Science does not verify or falsify theories by comparing them with a set of objective data found through observation. To some extent data are public and objective, but to a large extent the data depend on the theories (and the process of observation); no clear line separates observational from theoretical terms. A comprehensive theory of the world has to explain what it means by all its terms, and these meanings change. The most basic scientific concepts, like length, mean different things in different theories. Einsteinís length is a much more complicated quality than Newtonís. Theorists judge their theories on the basis of the data that the theories tell them is relevant.

Other features highlight the subjective aspects of science:

        Criteria besides observation exert some control over theories, despite the lack of specific rules for their unambiguous application. Scientists make subjective decisions about the elegance and coherence of their work.

        A scientific community can hold onto a theory threatened with discordant data. It might create auxiliary hypotheses to explain the data, for instance, or say the data are incorrect, or hope that someone will find something to undermine the rebel results. A comprehensive theory firmly resists falsification. A low-level law baldly stating relationships between observables lies more at the mercy of discrepancies.

Discordant data rarely overthrow fleshed-out theories. What will are alternative theories that have Ďgreater promise of explaining known data, resolving anomalies, and predicting novel phenomena.í[4] Newtonian mechanics, the triumph of pre-twentieth century physics, was well known to predict Mercuryís orbit incorrectly. Einstein superseded Newton, not astronomy.

Metaphysical assumptions lie at a yet higher level than theories, further away from direct empirical verification or falsification, but not immune to change. The arrival of new emphases in research traditions can change their metaphysics, or the acceptance of new traditions with difference basic ideas. The deterministic regularity of the universe itself is now questioned, thanks to the development of quantum mechanics. Changes in interest in science or other areas of human experience can also question the wider application of the metaphysical assumptions of a tradition.

The different facets of scientific knowledge (metaphysical assumptions, research traditions based on paradigms, comprehensive theories built from models, and laws that relate observables) can all change. The changes in each case are partly objective and partly subjective. This compromise reflects Barbourís philosophical position, which he calls critical realism, a compromise between naive realism and instrumentalism. We must step away from a severe logical empiricism if theology (a more obviously subjective enterprise than science) is to adopt the scientific method.

In Defense of Reason

To suggest theology adopts the method of the sciences rouses dispute. Polemics of late separate the two. Extreme empiricists, such as Dawkins, argue for the lack of worthwhile content in religion. Many religiously minded, in reaction, want to carve out an isolated niche for religious language. This attempt to defend theology stems from a fear that adopting scienceís method is to sell out to the enemy. But this enemyís bark is worse than its bite; Kuhn and others have manicured scienceís claws.

Theologians do face a challenge, however, if they adopt the scientific method: they need to understand how their discipline can be scientific. Not only must theology be rational, but also our experience of the world must ground it. Unsupported argument and fundamentalist faith may reside in the practice of religion, but theology, as a careful and academic study of our existence, must be empirical.

Theology is a constructive and reflective rational discipline. Religious adherents possess sets of beliefs, lives that are in some way religious, and a language in which they talk of matters religious. A theologian, a Christian theologian for instance, attempts to express and explain Christian beliefs in a rational, coherent, faithful, and systematic way. He or she accepts these aims and tries to explain certain phenomena. Theology is, in this most basic way, Ďfaith seeking understanding.í

Two twists complicate this picture. First, theologians can also play leader-roles for religious beliefs, language, and life. They can suggest matters a little beyond the commonly accepted belief system and so lead believers into that new area. Second, theologians can hold to and explain a set of beliefs other than those they would call Christian. Schubert Ogden accordingly believes that a theology should align itself with what is inherent in human existence, and this need not be Christian.[5] In such instances, however, Christian theologians attempt to make their constructions faithful to a set of beliefs they consider the essentially Christian.

Many object that theology should not or cannot seek truth in the manner of science. Three reasons supposedly support this.

First, theological theories cannot in principle be verified or falsified and are therefore not scientific. This stance could arise from subjectivism, which says that both theology and science are totally non-empirical. It could arise from a positivist-empiricist view, which diametrically opposes theological statements to those of science − the only truly empirical ones. Both extremes mislead. Objective and subjective factors exist in each of science and theology. Any extreme separation of the two distorts the reality.

Theologyís greater metaphysical content reflects its greater subjectivity as compared with science. Many take this to an extreme and talk of theology as if it were purely metaphysical. David Tracy suggests, for instance, that theological claims do not function in the same dimension as those of science because religious propositions ground all others and account for all experience.[6] Ordinary criteria of verification and falsification do not apply here. Tracyís argument misses, however, what Barbour points out: metaphysical concepts do relate to empirical evidence. They constantly change under its pressure because of shifts in theories and research traditions. Theology also seeks to explain not only the whole which is reality (which Tracy assumes), but also the constituent parts of it; this opens it to change as well.

The third reason for the apparent lack of the scientific in theology lies in its history. Theology used to make scientific assertions, laying out the physical structure of the cosmos and its means of creation. Powerful claims of empirical science found these theories wanting. Theology thus tries to distance itself from statements about the physical world and so save itself from further criticism. Existentialism appeared, along with demythologization, functionalism, language-game fideism, and other movements. To make its way back into suggesting scientific statements is not easy.

A theology can make scientific statements, including statements about the nature and creation of the physical cosmos, in several ways besides those we have already mentioned.

        What theological theories say about the meaning of life and history tests them. We can compare them with philosophical and historical, hermeneutical and phenomenological analyses.

        Theologies can rest on historical events, on knowledge of the structure of society, on human personality or psychology, on experiences claimed as common to all people. These are testable.

        Theologies have made such factual assertions as the coming of the end of the world at the year 2000, and that wealthy and successful people are so because of their good lives. They can state that the evolutionary process converges toward an Omega Point. These are testable.

        A theologian who advocates the anthropic principle − that we can read Divine purpose from the precise gearing of the universe for the generation of life − must listen to the cosmologists whose work may support or falsify the hypothesis.

Theology can make scientific claims for any part of its subject matter: human experience, history, and the physical, biological, and social world in all their facets. The methods and criteria of the relevant disciplines should evaluate these claims. A full and bold theology will attempt to explain in one coherent whole all that exists, and this will comprise statements proper to other disciplines and which those disciplines should evaluate.

Scientific Theology

Theology can be scientific. What would such a theology look like? What might we do to use the scientific method in theology?

The fundamental theological assumption, which defines theology as a discipline distinct from, say, biology or sociology, is theos. Theology centres on the idea ĎGodí (whatever we mean by that word); God is the organizational key, the idea that all others depend on and with which they fall in line. A theoretical system becomes a theology if its central, dominant, and hinge idea is an idea of God.

Now the problem looms. Theology seeks to study God, but how can it identify the reality of God to begin describing it?

We might identify the reality ĎGodí from the history of the wordís use. The theologian can attempt from this to isolate a cluster of attributes essential to God and areas in which human beings have and can experience God and Godís activity. This might enable the identification and description of God. Theology must take on board the additional metaphysical assumption that we can know God, at least imperfectly or in part.

God is not there to describe as is a physical object. But is theologyís job to describe God as we might describe the chair we sit in? If God were the sole subject matter of theology, suggests Wolfhart Pannenberg, theology cannot be a science.[7] ĎThe question arises,í he writes, Ďof how to distinguish God from the affirmations of theologians and already-committed believers.í[8] We must describe God in a more roundabout way than we do normal objects, and this gives ĎGodí a peculiar but not unique place in our language. Theology must have something else as its subject matter, and through this we can learn the nature of God.

And what is this subject matter of theology? Don Wiebe judges that theology concerns the world, Ďthe empirical world in its totality and the sum total of our personal experience.í It attempts systematically to account for and explain, not only religious experience (the Ďcategory of experiences which is other than mere sensationí), but all phenomena within the world, Ďthe daily round of experiences of which our life is made.í [9]

ĎGodí acts as a peculiar key concept for the explanations and understandings of theology. It fulfils its role as the starting point for theology just as another metaphysical assumption − that an objective and regular physical world exists − is the starting point for science. Natural science centers its explanations on the physical world. It believes that the world comprises such invisible things as physical forces and fields, and with existing and determining properties such as mass, velocity, valency, and so forth. Both science and theology try to explain the same object, but they use different media. Both look at (or describe) all of reality through their respective lenses of physical reality and God. The lenses act to isolate specific aspects of reality as central to explanation. Douglas Clyde Macintosh saw this back in 1919:

There is one presupposition peculiar to empirical theology, just as there is always one presupposition in every empirical science that is the special presupposition of that science. The empirical sciences assume the existence and the possibility of empirical knowledge of the objects they undertake to investigate. Thus chemistry assumes the existence of matter; psychology, the existence of states of consciousness; psychology of religion, the existence of religious experience, and so on. In each case there is assumed, commonly on the basis of pre-scientific experience, the accessibility of the object to further knowledge through further experience. And what is true of the sciences is true of empirical theology. . . .Ordinarily the empirical theologian, it may be expected, will posit the existence of God − defined, to be sure, in preliminary fashion − because he [or she] is already practically sure, on the basis of religious experience, that God really exists. . . .It is. . .what God is, that is to be investigated through scientific theological observation and experiment under the guidance of definite working hypotheses. [10]

Theologians create a theology centered on an idea of God. They then need to evaluate critically their construction with certain criteria, both as an individual theory and, to a greater extent, against competing theories.

This departs from past understandings of scientific method. Suppose we reject a theological theory that suggests we should castigate ourselves for sinning in all sorts of terrible ways though we, upright and good Christians, do not know we have. We would reject the theory only because we know of an alternative theological theory that makes more sense of our life as we experience it. In ways like this, we tend to hold to a theory (especially a comprehensive one) if no better alternatives exist, while we search for another.

Scientists have the courage to shoot as best they can toward the truth, but their success lies in their humility: they accept that they never hit the bullís-eye. The humble acceptance of our inadequacies is crucial for any intellectual pursuit, and is crucial for theology. As we hold dear our most valuable and useful beliefs, we must look to refine them.

Theological schools of thought give different degrees of importance to the criteria for evaluating theologies, though they draw from the same pool of criteria. Simplicity of formulation, aesthetic charm, the fruitfulness of the consequences − any human theory of the world, whether a scientistís or a theologianís − values these. The difficult issues arise as we consider the prime quality of a scientific theory − its command of supporting evidence. Here we enter a discussion of potential contrasts between science and theology.

Differences between Scientific and Theological Criteria and Methods

Differences between the ideas ĎGodí andĎthe physical worldí lie in our feeling the immediacy of the physical world, a sentiment which many used to feel (and some still do) toward God. We cannot point to God because we coin the word to explain a wider class of experiences, including human subjective experience, than those the idea of the physical world can explain.

Three other differences appear to distinguish the scientific and theological methods and their criteria.

The first concerns the use of and desire for mathematical models and theory in science. The lack of mathematics in theology says more about the humanities background of most theologians than about the potential for using mathematical models in it. Mathematical ideas may not even imply a quantitative approach as opposed to the qualitative one that matters human seem to require; theology usually fights such reductionism. The use of probability theory and statistics in sociology, for instance, suggest the usefulness of mathematics in human sciences.

The second contrast concerns the unanimity of science, the ability of scientific experiments to achieve more or less the same results wherever and whenever and by whomever they are performed, given the same initial conditions. The assumption that the physical world behaves with repeated consistency makes the derivation of general laws of nature possible. Thus any claim to factual truth is incompatible with purely private or idiosyncratic experience. This opposes theological Ďspecial caseí philosophy, which suggests that theology should not feel compelled to appeal to public criteria and method. God does what God wishes to do. The community of secular inquiry, however, rightly claims its rational procedures as the way to obtain truthful statements. It is repeated and careful examination of phenomena that lead to valuable knowledge. This applies to theology as well.

This returns us to the criterion of supporting evidence for theology and its most testing aspect: human experience. Earl MacCormac writes: ĎReligious language must be testable in the sense that common experiences must be available that are capable of interpretation in religious terms and symbols. Unlike science, these common experiences need not all be observable since much of religious expression involves feelings and desires.í[11] Tracy follows this path in his emphasis on the religious face of common human limit-experiences.[12] But Avery Dulles disputes this approach, asking about the place of extraordinary experiences: should these play a primary role in the evaluation of theological theories? Would this remove any chance of theology achieving unanimity?[13] MacCormac notes that religious experiences, though personal, are not purely subjective because many people share them. He refers to common religious experiences. We disagree with Dulles, but not necessarily conclude that all people must encounter religious and common human experience; many people must share them, however, for theology to have a public subject matter.

John Godbey writes that, between the contents of theologies that use the method and findings of the sciences, Ďcomplete unanimity is not to be expected [on scientific grounds], and, on religious grounds, . . .it is not to be desired. . .because of the absolutely indispensable nature of honesty in oneís religious witness.í[14] The proliferation of theologies and theological research traditions − each claiming truth and each based on different criteria, relative weights of criteria, and initial God-ideas − reflect the greater degree of subjectivity in theology than in science. Perhaps we should not expect complete unanimity in theology, given Kuhnís interpretation of rival and discordant research traditions in science. We should, on the other hand, expect much unanimity within each theological research tradition. Those who share common criteria, areas of evidence, and basic concepts should build their theological theory together, reaching plateaux of agreement.

The third and most important difference between scientific and theological criteria concerns predictability. Barbourís criterion of Ďsupporting experimental observationsí for science includes the valuing of a theory for its ability to yield Ďprecise predictions for future measurements.í No equivalent criterion exists in his list for religious beliefs. Scholars often cite this as the key distinction between science and theology, for the latter does not seek far ranging causal laws that allow for such predictions. Theology deals more with the unique unfolding of human history or of a personís life, the scholars continue, than with the repeating phenomena of nature.

A comprehensive theological theory resembles a metaphysical system. Much of theologyís corpus reflects on the nature of things in general, based on broad categories that include the idea ĎGod.í Theology is a higher-level act of knowing than science because it lacks the lower-level laws apparent in science. Frederick Ferrť admits that we cannot make predictions from metaphysical systems − a major difference between them and those of science − because their categories are general and they try to account for all types of phenomena, including those that occur in the future.[15] They leave nothing to compare them with. We cannot predict novel phenomena if we have already considered all types of experience. Thus, since theology is more akin to metaphysics than to the religious beliefs of Barbourís discourse, we should expect less of this scientific predictability than in science.

Yet one of the means by which Hugh Jones suggests we test a theological position lies in its fruitfulness to anticipate and plan for whatever lies in the future.[16] William Austin concludes that, when we test theological theories, Ďpredictions of future events play some role, at least in some traditions, but in general the role is secondary and ambiguous.í[17] Where theology deals with non-unique, repeating occurrences and causal laws, and in as much as it uses non-metaphysical categories, it can predict the future. With a higher-level focus, however, such theological predictions will probably not concern physical events, but peopleís actions. A theologian proposes a theology as a valuable and meaningful way for people to understand existence, including their own. The metaphysical claims of theologies refer to the world of the future as well as to that of the present. They will sink or swim on their relevance to the people of the future.

Science and Theology

The method we propose for theology provides a way for theology to attempt expressing truth. It should not claim, nor should any other method claim to lead to a complete account of truth. Knowledge is imperfect. Religious tradition after tradition stresses that perfect knowledge of reality lies beyond our reach. Science similarly admits it has not reached the truth, because it strives for better understanding. Truthfulness in science results in long-term, rational, and empirical arbitration between theories. We assume that science comes closer and closer to truth as scientific theories change. We assume that theology comes more and more to know the nature of God and Godís world as theological theories change. But we can only aim for truth; never can we know we are approaching it or have reached it. The scientific theological method will not provide a definitive description of reality viewed religiously. This method only provides the most adequate vehicle in our times for the expression of truth theologically.

The act of discovery is the key to all human knowing. So says Michael Polanyi. Knowledge progresses as we discover ever more about the world we live in. A sense of discovery exists in theology when it learns and encompasses new things. Theologians must involve themselves at the forefront of human knowing if they truly wish to discover and to seek understanding. Godbey writes: ĎTheology must wrestle with the best human knowledge available in the historical epoch in which a [theologian] writes. This admission. . .arises. . .out of a concern for the wrestle of theology with truth.í This wrestling, Godbey shows, has engaged many of the great theologians right down through the ages − Origen, Aquinas, Schleiermacher, Tillich, and, we add, C. S. Lewis. It must also engage us. Today, the method of science provides the Ďbest human knowledge available.í[18]

The core motivation for pursuing a scientific method in theology comes from a desire to do justice to and to minister to secular life and experience, to the theologianís secular being.

The scientific method is the paradigm in our modern western culture for producing truthful, useful, and perhaps meaningful knowledge − whether we like it or not. Theology dare not drift too far from that cultural placement of truth (even while fulfilling its task of criticizing secularity), else it (and its critique) will lose in meaning, worth to the community at large, and any relevant message or cutting edge it might have. Theologies should not side-step this challenge, but meet it head on, and adopt the scientific method. To do this would give weight and vibrancy to the theological enterprise and help theology face more openly the divide between fact and value. Our theology must be scientific to act as an effective moral force and means for directing and unifying our lives.

References

Austin, William. 1976. The Relevance of Natural Science to Theology. London: Macmillan.

Barbour, Ian G. 1974. Myths, Models and Paradigms: A Comparative Study in Science and Religion. New York: Harper & Row.

Dawkins, Richard. 1989. The Selfish Gene. Oxford: Oxford University Press.

Dulles, Avery. 1976. ĎMethod in Fundamental Theology: Reflections on David Tracyís Blessed Rage for Order.í Theological Studies 37 (2): 304-316.

Ferrť, Frederick. 1974. Review of Myths, Models and Paradigms by Barbour. Religious Education 69(6): 729-730.

Godbey, John C. 1970. ĎFurther Remarks on the Need for a Scientific Theology.í Zygon 5 (3): 194-215.

Jones, Hugh O. 1978. ĎGordon Kaufmanís Perspectival Language.í Religious Studies 14 (1): 89-97.

Kuhn, Thomas. 1962. The Structure of Scientific Revolutions. Chicago: University of Chicago Press.

MacCormack, Earl. 1976. Metaphor and Myth in Science and Religion. Durham, N.C.: Duke University Press.

MacIntosh, Douglas C. 1919. Theology as an Empirical Science. New York: Macmillan.

Ogden, Schubert M. 1966. The Reality of God and Other Essays. New York: Harper & Row.

Pannenberg, Wolfhart. 1972. ĎThe Nature of a Theological Statement.í Zygon 7 (1): 6-19.

_________. 1976. Theology and the Philosophy of Science. London: Darton, Longman, & Todd.

Tracy, David. 1974. ĎTask of a Fundamental Theology.í Journal of Religion 54 (1): 13-34.

_________. 1975. Blessed Rage for Order. New York: Seabury.

Wiebe, Don. 1976. ĎExplanation and the Scientific Method.í Zygon 11 (1): 35-49.

Notes



[1] Dawkins 1989: 1.

[2] Kuhn 1962.

[3] Barbour 1974.

[4] Barbour 1974: 114.

[5] Ogden 1966.

[6] Tracy 1975.

[7] Pannenberg 1972, 1976.

[8]Pannenberg 1972: 11.

[9] Wiebe 1976: 40, 42.

[10] MacIntosh 1919: 28-29.

[11] MacCormack 1976: 60.

[12] Tracy 1974.

[13] Dulles 1976.

[14] Godbey 1970: 200-201.

[15] Ferrť 1974.

[16] Jones 1978.

[17] Austin 1976: 8-9.

[18] Godbey 1970: 208.