John Wyclif's Trialogus was among the more widely disseminated of his works, and survives in eight manuscripts (six complete copies, a fragment, and a registrum) as well as sixteenth- and nineteenth-century printed editions. It is on the last of these, an edition published in 1869 by Gotthard Lechler, that Lahey bases his translation, although he has also consulted a manuscript to which Lechler did not have access. Lahey's translation sticks quite closely to Wyclif's Latin, and while the resulting English can be a little difficult to follow at times, the choice to remain close to the Latin seems a sound one in the end, as the amount of rewriting involved to render Trialogus into smoother, more idiomatic English would have made the project unwieldy, and Lahey's translation keeps the reader closer to the sense of the Latin original.
The volume includes a substantial introduction, with a brief overview of Wyclif's life followed by a discussion of the contents and aims of Trialogus. One of the more interesting and important points raised in this excellent introduction is that of its purpose and audience. It is quite clear that Trialogus was meant for a non-academic, but well-educated, audience--Lahey suggests lawyers, clerics, merchants, civil servants, Commons, and the lower nobility as possibilities--making Triaglogus akin to such popular theological tracts of the fourteenth century as Robert Holcot's Postilla super Librum Sapientiae, Thomas Bradwardine's De causa Dei contra Pelagium and Richard FitzRalph's De pauperie salvatoris. More intriguing still is Lahey's other suggestion for the intended audience of Trialogus: Wyclif's 'poor preachers.'
Lahey is well aware of the differing opinions about the existence of an organized band of preachers, sent out by Wyclif to preach the plain and simple Gospel.  His main opponent in this is Gillian Evans, whose main argument is that there does not seem to be anything explicitly linking Wyclif with such a band of preachers; we have no text outlining plans for this sort of program.  On the face of it, this seems a reasonable objection, and it is with this doubt that any advocate of the poor preachers must deal.
Lahey's argument is that Trialogus along with the Sermones, Opus evangelicum, and De mandatis divinis, form the basis of such a preaching program. The evidence for this lies first in the fact that extracts from these works form the basis for the commonplace books compiled by Wyclif's followers, the Floretum, the Rosarium sive floretus minor, and the Rosarium, and why these works might be chosen for such extraction. Following in the tradition of Augustine's Enchiridion and Aquinas' Compendium theologiae, these four works of Wyclif taken together can be seen as a guide to the Christian life and preaching formed on the basis of the theological virtues of faith, hope, and love. Trialogus covers faith; De mandatis, together with part of Opus evangelicum, one of his sermons, and another short treatise, all on the Lord's Prayer, examines hope; and De mandatis and Opus Evangelicum treats of love, which is the basis of the lex Christi, the nearest and dearest of the theological virtues to Wyclif's heart.
Wyclif's preachers, of course, would be a distinctly anti-fraternal group, even if they were modelled on the work of a friar, Aquinas. Their order would differ from those of Francis and Dominic in that their rule would not be manmade--it would be Scripture: "Given [Wyclif's] conviction that he had the pure and correct understanding of Scripture, it is likely that he would not have imagined that the four works discussed...could correspond to the artifice of the rules of Dominic or Francis" (16). I would argue further that Wyclif was not interested in forming an order in the conventional sense, unless it were an order of Christians informed by a correct understanding of scripture as rule of life, and the extreme importance of preaching in such a life. Such an "order" would be extremely difficult to distinguish from the general run of the population, as the history of heresy trials in later medieval England so well attests when it came to distinguishing Lollards from their neighbors. 
This is the crux of the problem: if Wyclif created an order of preachers, he did so on the basis of no manmade rule, and so left us no single, explicit text that would give us a definitive answer. However, there is some further evidence, as Lahey notes (262-263), on which we can base our opinion. There are, for instance, cross-references to the Sermones (262-263, 293), where the reader is directed for a fuller explanation of the topic at hand. These would seem to indicate that "Wyclif intended readers of Trialogus to have access to a collection of his sermons, supporting the hypothesis that the text was written to be a preacher's guide" (263, n. 15) In addition to this, the evidence from the Sermones themselves supports the idea that Wyclif had designs to create preaching aids and a preaching program; that the sermons themselves were meant for the use of other preachers is beyond question, the inclusion of such notes as "the material of the sermon should be expanded as it is expedient for the people listening," and "this material ought to be expanded as the simplicity of the people allows," are clear indications that the sermons were intended as a model sermon collection for the use of other preachers. 
Taken altogether, the evidence strongly supports Lahey's claim that Wyclif was writing for an audience of preachers, even if not with the intention of establishing an order in the conventional sense. Evans' contention that "Wyclif apparently did nothing so purposeful as to collect and send out disciples, although preaching certainly went on in his name"  becomes less tenable, as we can see that he was entirely intentional and purposeful in his composition of preaching materials. Thus, although the question of the existence of the poor preachers cannot be definitively answered one way or the other, there can be no real argument that Wyclif was not writing works with preachers, and a specific preaching program, in mind.
As to the actual contents of Trialogus, it is made up of four books, like Peter Lombard's Sentences, and Wyclif follows the Lombard's structure in a general way. He begins in book one with a discussion of the nature and attributes of God; in the second book he covers creation; in the third book he discusses virtue, vice, and the incarnation; and in the fourth book he covers the sacraments and the last things, with an aside of several chapters of anti-mendicant material included for good measure. Appended to this is the Supplement to the Trialogue, or On the endowment of the church, which discusses, as the title would suggest, the endowment of the Church through the Donation of Constantine, as well as the papal schism and the mendicant orders, and it is a general critique of the fourteenth-century church. The main work is dialogic in form, in this case, a three-way dialogue between Alithia (Greek for truth), Pseustis (Greek for liar), and Phronensis (Greek for wisdom), the last of whom stands in for Wyclif in the discussions. On the endowment of the church is not a dialogue, but rather a straightforward scholastic tract, and Wyclif might not have intended it to circulate with the Trialogus.
The first book of Trialogus is probably the most challenging to the modern reader, especially those who are unfamiliar with medieval theological methods. Wyclif spends a good deal of energy and time on the divine ideas, which he holds to be "the ontological basis for the universals he understood to organize all creation" (32). This is the key to Wyclif's philosophical theology, "which he expects his readers to adopt as necessary for their right understanding of Scripture and the Christian life" (32).
The second book reflects epistemological concerns, something common to Lombard and his commentators, which leads Wyclif to discuss the nature of human understanding, including the functioning of the senses (both interior and exterior), as well the soul, intellect, and will. Wyclif emphasizes that we understand the world around us through the apprehension of universals.
In his discussion of virtue and vice in the third book, Wyclif follows the traditional understanding of the virtues, drawing on the work of William Peraldus, O.P. (d. 1272) and rejecting the Ockhamist interpretation, which argued that a person could exhibit one virtue while being deficient in the others. Wyclif consistently rejected this sort of thinking, insisting on the interrelatedness of the virtues (and vices). Following this is a discussion of the Incarnation, which is the means of salvation and, thus, the basis for morality. The final section of book three deals with Scripture and hermeneutics, bringing to bear the philosophical insights of the first book.
The fourth book moves through the sacraments to the last things. The longest section of this book, a total of nine chapters, is devoted to the question of the Eucharist. This section contains a simplified version of Wyclif's understanding of the sacrament, but still elaborates on Wyclif's rejection of transsubstantiation and his avowal of a remanationist position. The other sacraments are treated in turn, but there is nothing in those chapters quite so controversial as Wyclif's attacks on transubstantiation. Much time towards the end of this book is spent attacking the four mendicant orders, before closing with a discussion of the Resurrection, the Last Judgment, and the final state of the damned and blessed.
The work thus covers the entire range of medieval scholastic theology in a format meant to be accessible to an educated, if non-university, audience. And this is more or less what Lahey presents to his readers--an accessible, if sometimes difficult and challenging, overview of the essentials of Wycliffism straight from the founder's pen. There is many a useful insight into Wyclif's thought and system in Trialogus, and anyone interested in understanding the controversial figure could do far worse than give it a thorough and careful reading.
1. See Stephen E. Lahey, John Wyclif (New York: Oxford University Press, 2009), 165-168.
2. Gillian R. Evans, John Wyclif: Myth and Reality (Downer's Grove, IL: Intervarsity Press, 2005), 250-254.
3. A good introduction to this subject is J. Patrick Hornbeck II, What is a Lollard? Dissent and Belief in Late Medieval England (New York: Oxford University Press, 2010).
4. John Wyclif, Sermones, 4 vols. (London: Wyclif Society, 1887-1890; New York: Johnson Reprints, 1966), vol. 1, 130/30-31 and Sermones I. 133/11-12. See also Anne Hudson, "Aspects of the 'Publication' of Wyclif's Sermons," in Late-Medieval Religious Text and Their Transmission: Essays in Honour of A.I. Doyle, ed. Alastair J. Minnis (Woodbridge, UK: Brewer, 1994), 121-130; and eadem, "Wyclif's Latin sermons: questions of form, date and audience" Archives d'histoire doctrinale et littéraire du moyen âge 68 (2001): 223-248.
5. Evans, Myth and Reality, 254.