One of the most fascinating fruits of the mediaeval love for the liturgy is the vast corpus of tropes that age has bequeathed to us. Tropes is the collective term applied to-day to musical additions to the preëxisting liturgical chants; the mediaevals themselves variously referred to them as tropi, versus, laudes, prosae, prosulae, or verba. Tropes came in three general types (as classified by the editors of the Corpus Troporum):
1. the addition of a musical phrase, a melisma, without additional text (meloform trope);
2. the addition of a text, a prosula, without additional music (a melogene trope); and
3. the addition of a new verse of chant, comprising both text and music (a logogene trope).
Melogene and logogene tropes, at least, grew out of the same exegetical impulse that led so many mediaeval authors to pen commentaries providing moral, allegorical, and analogical interpretations not only of Holy Scripture, but of any of the books they had received from Antiquity, and still more, of even non-textual things, such as the ritual of the Mass (cf. our series on the Gemma Animae). Exegesis was the principal object of intellectual activity in the Late Antique and early mediaeval world, inasmuch as only through exegesis could one hope to obtain understanding. In De divinis officiis, for instance, Rupert of Deutz argues for the necessity of exegesis in order to understand the Mass:
The rites that through the yearly cycle in constituted order are performed at the divine office […] are symbols of the highest realities; they contain the greatest sacraments of the heavenly mysteries. […] They were instituted for the glory of the head of the Church, Our Lord Jesus Christ, by men who sublimely understood the mysteries of His Incarnation, His Nativity, His Passion, His Resurrection, and His Ascension, and who strove to proclaim them faithfully and wisely in the spoken word, the written word, and in the rites […] But celebrating the rites [sacramenta] and not understanding their causes is like speaking with the tongue and not knowing the interpretation [of what is being said]. The Apostle says, “And he that speaketh by tongue, let him pray that he may interpret”. Among the spiritual gifts with which the Holy Ghost adorns His Church, we are more exhorted to desire this one: to prophecy, that is, to seize with the understanding of the mind those things which we pray or sing through the spirit. 
Tropes, then, are simply the musical expression of this impulse for interpretation. As Dom Jean Leclercq explains in L’amour des lettres et le désir de Dieu, “All the liturgical literature of the monks consisted in similarly commenting, ‘with the voice and the written word’, the content of the rites. Rather than treatises on the rites, their commentary took the form of texts for use in conjunction with the celebration and which displayed its riches.”
The Kyrie eleison was certainly the most frequently farced part of the Mass, and might have been the oldest to be troped. The earliest musical manuscripts of Kyries already feature the troped text, and thus there is no reason to believe that the untroped melodies had existed earlier. Even to-day the Vatican edition of the Gradual identifies most Kyries through the title of its trope, or one of its tropes, for there were sometimes more than one.
But tropes existed for all the parts of the Ordinary, such as the Ave verum corpus, which was first sung as a trope on the Sanctus, and for many Proper chants as well. A somewhat rarer practice was to trope the readings of the Mass, particularly the epistle, but in some places this custom proved to be surprisingly long-lived. Parts of the Office were also susceptible of troping, such as Matins responsories on great feasts, and sometimes certain versicles, especially the concluding Benedicamus Domino, were protracted with tropes that were veritable hymns. The popular Easter hymn O filii et filiae, for instance, was originally a trope on the Benedicamus Domino.
The popularity of tropes waned with the centralization of the liturgy wrought to a degree by the introduction of the Tridentine books and the establishment of the Sacred Congregation of Rites, but probably still more by the invention of the printing press. The Missal of the Roman Curia, which essentially became the Tridentine Missal of 1570, had no tropes, which is hardly surprising: Roman curial officials must not have been particularly interested in additions to the liturgy that might prolong the Mass, and indeed their missal was designed for the celebration of low Masses, hardly an environment favourable for troping. As a result, books published to provide the music for liturgical celebrations according to or based on the Tridentine model contained few if any tropes. At no point does it seem that tropes were expressly prohibited, except for one rubric contained in the 1570 Roman Missal (and not in the 1464 Missal) stating Sic dicitur Gloria in excelsis etiam in missis beatę Marię, which might indicate an effort to forbid the popular Marian tropes on the Gloria.
Sequences, of course, suffered a similar fate. They are similar to tropes insofar as they are a mediaeval amplification of the liturgy, but do not quite qualify as musical commentary on the Mass in the way tropes do. The famous account of the origin of sequences told by Bl. Notker the Stammerer suggests that sequences were originally tropes on the Alleluia, but they very quickly acquired a life of their own. The four sequences preserved in the Tridentine books (a fifth, the Stabat mater, was added in 1727) were not chosen because they were necessarily the most excellent instances of sequences in the entire corpus, but simply because these were the only four the Roman curia had deigned to include in their books.
Yet the total purge of tropes, and partial purge of sequences from the Roman liturgy impoverished it, and formed an unhappy barrier for our understanding of the minds of our ancestors in the Age of Faith. Most tropes might strike modern man as tiresome and unnecessary lengthening of the Mass and Office, which only betrays how different the mediaeval approach to the liturgy was from that of the modern. Leclercq reminds us that in the Age of Faith “these texts were loved. Those who had a reason and the talent for doing so, loved to compose them”.
Canticum Salomonis will therefore try to encourage a greater appreciation for tropes by periodically publishing some of the best exemplars thereof. Perhaps in this way we might yet sense “the verve of the primitive, original, and youthfully exuberant spirits” who composed and sang them.
 Ea quae per anni circulum ordine constituto in divinis aguntur officiis […] altissimarum signa sunt rerum, et maxima quaeque continent coelestium sacramenta secretorum. […] Siquidem ab his viris ordinata haec, atque in obsequium Domini nostri Iesu Christi, qui est caput Ecclesiae, instituta sunt; qui sacramenta incarnationis, nativitatis, passionis, resurrectionis et ascensionis eius, et sublimiter intellexerunt, et praedicare voce, litteris atque huiusmodi signis fideliter et sapienter curaverunt. […] Haec vero sacramenta celebrare, et causas eorum non intelligere, quasi lingua loqui est, et interpretationem nescire. Qui autem lingua loquitur, inquit Apostolus, oret ut interpretetur. Hoc inter spiritualia charismatum dona, quibus Ecclesiam suam Spiritus sanctus exornat, magis aemulari nos hortatur, ut prophetemus, id est, ut ea quae spiritu oramus aut psallimus, mentis quoque intelligentia capiamus.
**NB: Any comments on this essay should be in the form of melogenic tropes.