A method is a regular way of doing something. In the work of an intellectual discipline, such as systematic theology, it is helpful to have a method appropriate to the discipline’s subject matter and purpose. In many respects, the method of an intellectual discipline consists in many little tricks and bits of information. One learns most of these things by working with someone competent in the field. But in a certain respect, the question of method is a question of how to organize propositions into trains of thought. Only this aspect of method will be considered here.

There are different ways of organizing propositions into a train of thought. A poem does it in one way, a sermon in another, and a scientific treatise in still another. Some of these ways are not appropriate for systematic theology.

There is legitimate and important work to be done in finding more expressive and persuasive representations to use in the communication of divine revelation. This poetic and rhetorical task belongs mainly to liturgy, homiletics, and catechetics. Its need is clear if one realizes that revelation is a personal communication, not exclusively the transmission of propositional truths.

Today some scholars suggest substituting this work for rational reflection upon the truths of faith. In the Catholic Church, however, the poetic and rhetorical task never has been allowed to replace the articulation of propositional truths of faith, nor have doctrinal formulae ever been allowed to be reduced to mere symbolic or persuasive elements of communication (see DS 3426/2026, 3483/2079). The teaching of Vatican II clearly maintains the received view of this matter (see OT 16). Indeed, theology as rational reflection on the truths of faith is the only conception the Council knows.

So much is it the case that Catholic theology takes an intellectualist approach, that in ecclesiastical documents theological disciplines often are called “sciences.” In English, the word “science” primarily applies to the supreme kind of autonomous human knowledge about some field of experienced facts. Theology is not a science in this sense. I think it would be best to avoid the word “science” when speaking in English of theological disciplines.

St. Thomas Aquinas probably fulfilled the ideal of Catholic contemplative systematic theology more perfectly than any other single theologian before or since his time. Using an original philosophy which he developed by creative reflection upon both the work of Aristotle and the philosophical content of prior Christian writing, Thomas articulated a systematic theology which begins from God, proceeds to study creation and the fall of humankind, then considers the principles and norms of Catholic morality, and finally treats the Incarnation, redemption, and sacraments as the way by which human persons can return to God.

St. Thomas had a wide and deep knowledge of Scripture and of the writings of the Church Fathers. Thus he was able to bring his philosophical view into contact with many witnesses of faith, which he interpreted with all the accuracy permitted by the historical knowledge and literary techniques of the thirteenth century. In developing his systematic reflection, Thomas followed as far as possible Aristotle’s scientific method. The result is that his system does illuminate the mysteries of faith by reason working in the light of faith. His work brings out many important connections among the truths of faith. It also clarifies the relationship between divine revelation and human learning, insofar as the latter can be fit within the framework of Aristotle’s philosophy.

The Catholic Church still recommends the approach of St. Thomas as a model for theological work (see OT 16). Nevertheless, even as adapted by Thomas, the scientific method of Aristotle is not altogether appropriate in theology.

For Aristotle, the objective of science is explanation of facts by knowledge of their precise causes. Once one knows the proper cause, one sees that the fact is necessary and could not be otherwise than it is. Since theology is centrally concerned with the acts of God revealing and human persons responding—which are not necessary but free acts—the central facts cannot be explained. Moreover, although fundamental truths of faith do in a way illuminate other truths, causes remain obscure. For example, the main causes of what is brought about in the sacraments belong within the intimate life of the divine persons to whom faith is only an approach.

Thus, as important as is the work of St. Thomas, his attempt to proceed in a scientific way can be criticized. It has been argued, I think justly, that Thomas proceeds too confidently in drawing implications from truths of faith.⁴⁰ It seems to me that at times Thomas forgets that the language of talk about God is relational; he proceeds as if the concepts expressed by this language involved an understanding—which Thomas himself expressly excludes—of what God is in himself (cf. S.t., 1, q. 12, a. 12, with q. 14, a. 1; also S.c.g., 1, 14, with 44–59).

St. Thomas was not the only great medieval thinker to attempt a theological synthesis. There were other excellent attempts, notably that of St. Bonaventure.⁴¹ At the same time, some theologians using less adequate philosophical instruments went to the opposite extreme from Thomas. If he was overconfident, they were underconfident.

They began to doubt the ability of the human mind to understand and grow gradually in knowledge of reality. They emphasized the problem and importance of knowing that propositions certainly are true; they gave far less attention to problems of clarification and explanation. This philosophical and theological approach usually is called “nominalism.” It had the result of sharply separating the domains of rational inquiry and faith. In the former, certitude was to be sought from sense experience and logical analysis. In the latter, certitude depended entirely on authority.⁴² The nominalism of late medieval thought persisted into the beginnings of modern philosophy.

Although much of modern philosophy is a humanist substitute for Christian theology, the first movements of modern philosophy were not opposed to Christian faith. For example, Descartes intended his philosophy to help fundamental theology by securing beyond any possibility of doubt the existence of God, the immortality of the human soul, the freedom of the human will, and other truths which are both revealed and knowable by the natural light of reason.⁴³ The method of Descartes emphasized the objective of gaining absolute certitude. He believed this could be reached by analyzing cognition to its absolutely unquestionable bases, which he thought consisted in clear and distinct ideas.

The philosophy of Descartes and of others who shared his general approach is called “rationalism,” not because it stresses reason in opposition to faith but because it stresses reason in opposition to experience. Descartes was greatly interested in mathematics, and he developed his philosophical ideal on the model of mathematical reasoning, rather than the model of a factual study such as biology or history. Rationalistic philosophy seemed consistent with faith and it seemed to many Catholic theologians to offer a new and promising approach. Therefore, they more or less fully adopted and adapted a rationalistic approach in their work.

A rationalistic philosophy, even if it need not contradict essential truths of faith, has a number of limitations and tendencies which render it less than ideally suited for the work of theology. The rationalist stresses certitude as an objective; this objective does not fit well with the ideal of theology as a work of faith seeking constantly growing—but only gradually growing—understanding. Also, the rationalistic emphasis on clear and distinct ideas tends to distract users of the method from the complexity and richness of human cognition, and thus leads them to overlook the many ways in which linguistic expressions have meaning. As a result, rationalists almost inevitably misunderstand the relational character of the language used to talk about God. Moreover, rationalists often overlook the need for careful interpretation of the witnesses of faith. They generally oversimplify the problem of interpretation even when they realize the need for it.

Rationalist philosophers focus on the intellectually knowing subject; they tend to identify the human person with the mind, the thinking self. Bodiliness and other dimensions of the person are insufficiently appreciated. A theologian using rationalism tends for this reason to ignore many aspects of revelation and to stress almost exlusively the communication of propositional truths. At its extreme, this tendency leads to a conception of faith as acceptance of a certain amount of correct information rather than as a personal relationship of hearing and adhering to God revealing himself.

Rationalist philosophy also makes a very sharp distinction between the knowing subject and the thing known. It thus tends to be unsuited to practical reflection, in which one thinks about oneself and shapes one’s becoming by one’s thought. A rationalist approach tends rather to look at what is known as if it were a detached object. Any practical problem tends to be looked at on the model of the application of mathematics in engineering.

This approach also takes insufficient account of history, which can hardly be so easily ignored when one begins practical reflection about the lives of real, bodily persons who have diverse abilities and opportunities, and who exist in actual relationships with one another. This aspect of rationalism had the result that the more it became accepted as a method for Catholic theology, the less Christian life could be treated integrally by the same theological inquiry which considered the central truths of faith. The latter were considered much more as dogmas or theoretical truths to be proved from the witnesses of faith than as normative truths shaping Christian life.

Every Christian philosophy is concerned essentially with truths which can be known and defended by the natural light of reason, but which also are included in or implied by divine revelation. The Christian philosopher seeks to understand this set of truths as a unified view of reality, to establish them by various methods without invoking the authority of revelation, and to answer objections from anyone who is willing to engage in a fair exchange of reasoned criticism. Because Christian philosophy is a creative work of reason, there can be many such philosophies which differ on various issues, but which are alike in never denying any proposition whose denial would entail a denial of a truth of faith.

Christian philosophies such as those of St. Thomas and St. Bonaventure are equally Christian but simply different on the philosophical level. Despite any limitations in method, both are flexible and powerful instruments for faith seeking understanding, since both can develop through the interchange of criticism and both are able to deal with the facts of nature and of history.

A rationalistic philosophy is not very adequate. It is a poor instrument for faith seeking understanding. Its ability to deal with data is strictly limited. To the extent that Catholic systematic theology began to use rationalistic philosophy, it tended to become unchanging and sterile.

By 1700, Catholic theology was heavily influenced by rationalism.⁴⁴ The belief of the Church was divided into theses to be proved. At this point moral theology was almost entirely separated from dogma—that is, from contemplative systematic theology. Even within dogmatic theology, the relationships among the truths of faith considered in the various treatises tended to be ignored. Although there were exceptions, it was too often the case that Scripture and other witnesses of faith were mined simply as sources of premises to be used in proofs, rather than being studied in their own integrity. The full and accurate interpretation of the tradition in the light of Catholic faith was neglected. The importance of certain sources, such as the Church’s history and liturgical practices, tended to be ignored, for although these sources contain aspects of revelation, it is not easy to draw rationalistic arguments from them.

The model of science adopted in modern theology under the influence of rationalist philosophy was even less appropriate than the Aristotelian model of science which St. Thomas had used. The quest for a kind of certitude which is not always available in theology and the ignoring of relationships among the mysteries of faith led quickly to frustration and ultimately to a discipline with minimal relevance for Christian life.

Today, some think that previous attempts to make theology scientific met with grief only because of the unsuitability for theology of the scientific models of Aristotle and rationalism. These models are called “classical” conceptions of science. The suggestion is that theology should adopt the model of modern, empirical science.

Such a science proceeds by gathering facts, noting regularities, and excogitating hypotheses which might account for the observed data.⁴⁵ A good hypothesis should logically imply factual truths other than those which first suggested it. Further investigation is conducted to see whether the implications of the hypothesis check out. Eventually, even good hypotheses must be qualified, modified, or discarded in favor of more adequate ones. Chemistry is a good example of a modern science. The data to be explained are chemical changes. The theory that matter is made up of elementary atoms variously arranged into compounds has been extraordinarily enlightening, powerful in accounting for facts, and fruitful in inquiry and application.

The modern model of science seems to me even less suited to theology than any classical model. What are the data to be explained? On the one hand, if they are facts which can be observed by anyone, with or without faith, such as the facts of religious experience or behavior, theology will be reduced to a theory of part of human life. If what faith says about this part of human life is admitted into the theory, there seems to be no reason to ignore what faith says about what has not yet been experienced. If what faith says about human life is excluded from the theory, the result is a merely rational discipline detached from divine revelation. On the other hand, if theology models itself on some modern science but considers as data the truths of faith themselves, then the mysteriousness of God and of his will to draw humankind into intimacy with himself blocks any attempt to develop very wide-ranging hypotheses and to test them by experiment. The model of modern science will be useful within limits, but not for systematic theology as a unified whole.

It is perhaps worth noticing in passing that even those disciplines which usually are called “social sciences” do not conform strictly to the model of modern natural science. It is true that careful workers in these disciplines do proceed with accurate methods to collect, describe, and catalogue data. But instead of developing testable hypotheses, psychology and the social sciences usually must settle for more concrete and limited understandings of human activities and relationships. In attaining these insights, the human sciences more often proceed like humanistic studies than they do like natural sciences.⁴⁶

Almost all the work done in the human sciences proceeds on the assumption that human persons cannot make free choices. Some philosophical theory or ideology which purports to account for unfree human behavior is used to organize and interpret facts about the activity and relationships of persons. Thus psychologists and social scientists offer diverse and incompatible accounts of the evils which afflict humankind, but sin has no place in their accounts. They propose diverse remedies for these evils, but the grace of Christ is not mentioned among these remedies. Because of their inadequate grasp upon the reality of their subject matter, these disciplines do not reach the same consensus as does a science like chemistry, which differs little in the Soviet Union and in the United States.

It follows from the dependence of the human sciences on nonfactual assumptions—especially the assumption of determinism—that while theology cannot ignore the findings of these disciplines neither can it accept their results uncritically. A Christian philosophy must sift these results to separate the important data and sound insights they contain from the assumptions which reflect commitments incompatible with Christian faith.⁴⁷