By Fr. Robert Solon, Jr.
John Henry Newman. During his Anglican period, Newman wrote an extensive analysis of the Arian heresy titled The Arians of the Fourth Century, in which he appended a Note titled “The Orthodoxy of the Body of the Faith During the Arian Supremacy.” He introduces an impressively long list of excerpts from Patristic authors describing both the persecution of Arians against the Catholics, as well as the Catholic resistance in return, as follows: “The Catholic people, in the length and breadth of Christendom, were the obstinate champions of Catholic truth, and the bishops were not….[b]ut on the whole, taking a wide view of the history, we are obliged to say that the governing body of the Church came short, and the governed were pre-eminent in faith, zeal, courage and constancy.” Although the disputes of Arianism were doctrinal and centered around the accepted text of the Creed, the concept of the fidelity of the on-the-ground priests and people is an echo of Prosper’s original formulation: “Perhaps it was permitted [the temporary Arian ascendency and persecutions] in order to impress upon the Church at the very time passing out of her state of persecution and to her long temporal ascendancy, the great evangelical lesson, that, not the wise and powerful, but the obscure, the unlearned, and the weak constitute her real strength.”
More directly, in the late 1840s, after Newman had converted to Roman Catholicism, he would return to the idea of the census fidelium and suggest an authority (but certainly not all or final authority; that was reserved for the magisterium) for both the people and the liturgy in his essay “On Consulting the Faithful in Matters of Doctrine.” While defending his use of the word “consult” as a non-technical usage in an article on the doctrine of the Immaculate Conception in another publication, he noted the following (emphases mine):
I think I am right in saying that the tradition of the Apostles, committed to the whole Church in its various constituents and functions per modum unius manifests itself variously at various times: sometimes by the mouth of the episcopacy, sometimes by the doctors, sometimes by the people, sometimes by liturgies, rites, ceremonies, and customs, by events, disputes, movements, and those phenomena which are comprised under the name of history. It follows that none of these channels of tradition may be treated with disrespect; granting at the same time fully, that the gift of discerning, discriminating, defining, promulgating, and enforcing any portion of that tradition resides solely in the Ecclesia docens.
Gregory Dix. In 1945 an Anglican monk of Nashdom Abbey published a significantly expanded version of a paper originally delivered to the Society of St. John the Evangelist at Cowley on the Eucharist and its actions. Entitled The Shape of the Liturgy, for possibly the first time the now-classic four-fold action of taking, blessing, breaking, and distributing of the Eucharistic Bread and Wine was described and explicated in both historical but also theological terms. As an example of mid-20th-Century lex orandi-lex credendi theology, and just at the cusp of the Liturgical Renewal Movement, which was even then breaking forth from Maria Laach and elsewhere, Dix’s work stands as a seminal work in liturgical theology.
Alexander Schmemann. During the height of the Liturgical Movement and while Vatican II was sitting, in 1966 Fr. Alexander Schmemann wrote a little introduction to Orthodox liturgy titled Introduction to Liturgical Spirituality. Widely cited by two generations of liturgical theologians since then, Schmemann’s Introduction offers a cogent overview of both Orthodox and Western views of the liturgical movement. His definition of liturgical theology itself is very much of a lex orandi first, then lex credendi approach:
Theology is above all explanation, ‘the search for words appropriate to the nature of God’ i.e., for a system of concepts corresponding as much as possible to the faith and experience of the Church. Therefore the task of liturgical theology consists in giving a theological basis to the explanation of worship and the whole liturgical tradition of the Church. This means, first, to find and define the concepts and categories which are capable of expressing as fully as possible the essential nature of the liturgical experience of the Church; second, to connect these ideas with that system of concepts which theology uses to expound the faith and doctrine of the Church, and third, to present the separate idea of liturgical experience as a connected whole, as in the last analysis, the ‘rule of prayer’ dwelling within the Church and determining her ‘rule of faith.’
Therefore the task of liturgical theology consists in giving a theological basis to the explanation of worship and the whole liturgical tradition of the Church.
For Schmemann the importance of the liturgical movement lies in “the genuine discovery of worship as the life of the Church, the public act which eternally actualizes the nature of the Church as the Body of Christ, an act moreover, that is not partial…but which embraces, expresses, inspires, and defines the whole Church, her essential nature, her whole life. ‘The Christian religion is not only a doctrine…it is a public action or deed.’” If the Church is the Church first and foremost in and because of its public worship, then for Schmemann the theology drawn from its worship and expressed by it must be of signal importance indeed.
Geoffrey Wainwright. In 1980 the Methodist theologian Geoffrey Wainwright brought out Doxology, subtitled The Praise of God in Worship, Doctrine, and Life. He is one of the more important authors to directly address the idea of lex orandi-lex credendi, and actually titles a chapter in his book to each part of the phrase, with key sections identifying the provenance and historical usage of the concept. This book is the first (or nearly the first) in the Liturgical Movement to attempt a systematic theology centered and drawn directly from Christian worship. Possibly more important than the history of the phrase is the observation that lex credendi and lex orandi exist in tension or balance with one another, rather like a see-saw, and that at various times in Western Christianity either phrase has been more ascendant over the other.
Aidan Kavaunaugh. The 1980s was the first great period of reflection on what the West had gone through in the 1960s and ‘70s with the great reforms of Vatican II and the new worship books in the Church of England, the US Episcopal church, the US Lutheran Churches, and elsewhere. A Benedictine, Fr. Kavanaugh clearly articulated for the first time the important concepts of theologia prima, the enacted liturgy itself while it is being enacted, and theologia seconda, the interpretation of the acts post-enactment, in his 1984 work On Liturgical Theology. Drawing from Schmemann, he noted that it is the performed or enacted liturgy which is the first theology of the Church; what we derive from that is secondary, and although no less important, not to be confused, conflated with, or superior over the actual worship of the Church on its daily, weekly, seasonal, and yearly rounds.
Leonel Mitchell. In his 1991 book aptly named Praying Shapes Believing, Prof. Mitchell opens with an explicit acceptance of lex orandi-lex credendi liturgical theology, and than uses that to perform theologia secunda on the texts of the 1979 Book of Common Prayer. Essentially, what Wainwright does generally with and from worship is what Mitchell does with and from the U.S. Prayer Book specifically, and is an excellent example of liturgical theology based on modern texts.
Don E. Saliers. Prof. Saliers’ Worship as Theology of 1994 has as its explicit thesis: “Christian liturgy as rite and as prayer is thoroughly eschatological. How this is so is the burden of my investigations. Can the study of liturgy contribute to the renewal of church and theology in our age?” In his second and central section he explores four foci of liturgical action: praising thanking and blessing; invoking and beseeching; lamenting and confessing; and interceding; all with God as both subject and/or object.
Gordon W. Lathrup. Lutheran pastor and theologian Gordon Lathrup adds a third theology to the primary and secondary theology of liturgy in his Holy Things: A Liturgical Theology. For him, pastoral liturgical theology is actual evaluation of actual performed rites in actual communities, and not simply the examination of rubrics or texts themselves, standing alone. He uses an extended example of “Leviticus vs. Amos,” in which Leviticus 14 describes the rite needed to accept a cleansed leper back into the community, while Amos proclaims that God hates all of our rites and ceremonies when there is no justice. This tension sets up a pattern where we can examine the balance between the two in the life of the Church.
David Fagerberg. As a member of the second generation of liturgical theologians, David Faberberg’s 2004 Theologica Prima: What is Liturgical Theology? (an expansion of his doctoral dissertation and now in its second edition) resystematizes liturgical theology with multiple references to lex orandi-lex credendi. Using his own systems and definitions, he examines two historical examples of liturgical theology, one from the third century (Germanus) and one from the 20th (Schmemann).
James Farwell. As liturgical theology continues to mature, scholars have begun to concentrate on specific rites. James Farwell, now at Virginia Seminary, does so with the central ceremonies of the Christian year in This Is The Night: Suffering, Salvation, and the Liturgies of Holy Week, from 2005. He specifically explores the soteriology expressed in the Holy Week rites along with the concepts of human and divine suffering.
Two anthologies round out this summary of theologians working in liturgical theology. The Identify of Anglican Worship was published in 1991 and contains a number of articles on general characteristics of Anglican liturgies as well as specific rites, such as the Eucharist, the Offices, and the Pastoral Offices. It is primarily focused on the Western liturgies. The second, from 2000, is Primary Sources of Liturgical Theology: A Reader, edited by Dwight Vogel, and is an excellent overview of the field from every author already cited above plus others. This would be a fine book in a survey course on liturgical theology or simply as an introduction to the topics involved. 
The change in the relative importance placed on lex orandi or lex credendi over time, as summarized by the above authors and sources, can be illustrated easily as well:
…Lex Orandi has regained almost all its pre-eminence in theology and as liturgical theology.
Essentially, we have come almost full circle: If the Patristic period was the first zenith of Lex Orandi, then the Reformation was its nadir for both Protestants and Catholics of the time, and with the rise of Prayer Book Revision and the Oxford Movement of the 19th Century through to the Liturgical Renewal movement of the 20th, Lex Orandi has regained almost all its pre-eminence in theology and as liturgical theology. Indeed, the Liturgical Movement itself is Lex Orandi-Lex Credendi writ large: if theology were not discernible from liturgy, and should not actually be drawn from liturgy, then there would have been no need to reexamine our liturgies anyway except as comparisons with those of the past.
 John Henry Newman, The Arians of the Fourth Century (South Bend: University of Notre Dame Press 2001, reprint from 1833) 445
 Newman, Arians, 446
 John Henry Newman, “On Consulting the Faithful in Matters of Doctrine,” Conscience, Consensus, and the Development of Doctrine: Revolutionary Texts by Cardinal Newman, (New York: Doubleday 1992) 398
 Dom Gregory Dix The Shape of the Liturgy (London: Dacre Press 1945) 48
 Alexandr Schmemann, Introduction to Liturgical Theology (Crestwood, NY: St. Vladimir’s Seminary Press, 1986, c1966) 17, emphases mine.
 Schmemann 14, internally quoting L. Bouyer Le Mystere Paschal (Paris: Les Editions du Cerf 1947) 9.
 Wainwright, Doxology 218-283
 Aidan Kavanaugh, On Liturgical Theology, (New York: Pueblo Publishing Co., 1984)
 Leonel Mitchell, Praying Shapes Believing: A Theological Commentary on The Book of Common Prayer (Wilton CT: Morehouse Publishing 1985)
 Don E. Saliers, Worship as Theology: Foretaste of Glory Divine (Nashville: Abingdon Press 1994)
 Gordon W. Lathrop, Holy Things: A Liturgical Theology (Minneapolis: Fortress Press 1998)
 David W. Faberburg Theologia Prima: What is Liturgical Theology? (Chicago: Liturgy Training Publications/Hillebrand Books 2004)
 James Farwell This Is the Night: Suffering, Salvation, and the Liturgies of Holy Week (New York: T&T Clark 2005)
 Kenneth Stevenson and Bryan Spinks, eds., The Identify of Anglican Worship (Harrisburg: Morehouse Publishing 1991)
 Dwight Vogel, ed., Primary Sources of Liturgical Theology: A Reader (Collegeville: The Liturgical Press 2000)
 Adopted from both Irwin and Wainwright