Canon law was more studied and better understood; writings multiplied, some of an historical nature, others practical, according to the inclination of the authors.
But, while compilations of texts and official collections were available for Roman law, or "Corpus juris civilis", Gratian had no such assistance.
He therefore adopted the plan of inserting the texts in the body of his general treatise; from the disordered mass of canons collected from the earliest days, he selected not only the law actually in force (eliminating the regulations which had fallen into desuetude, or which were revoked, or not of general application) but also the principles; he elaborated a system of law which, however incomplete, was nevertheless methodical. the methodical and coordinated knowledge of ecclesiastical law, was at length established.
Finally, if we look to the history or chronological evolution of canon law, we find three epochs: from the beginning to the "Decretum" of Gratian exclusively; from Gratian to the Council of Trent; from the Council of Trent to our day.
The law of these three periods is referred to respectively as the ancient, the new, and the recent law ( As we shall see in treating of the gradual development of the material of canon law (see below, IV), though a legislative power has always existed in the Church, and though it has always been exercised, a long period had necessarily to elapse before the laws were reduced to a harmonious systematic body, serving as a basis for methodical study and giving rise to general theories.
This plan, popularized by the "Institutiones juris canonici" of Lancellotti (1563), has been followed since by most of the canonist authors of "Institutiones" or manuals, though there has been considerable divergence in the subdivisions; most of the more extensive works, however, preserved the order of the "Decretals". In later times many textbooks, especially in Germany, began to adopt original plans.
In the sixteenth century too, the study of canon law was developed and improved like that of other sciences, by the critical spirit of the age: doubtful texts were rejected and the and tendency or intention of later laws traced back to the customs of former days.
At an early period we meet with expressions referring to the body of ecclesiastical legislation then in process of formation: ); however, strictly speaking, there is a slight difference of meaning between the two expressions: canon law denotes in particular the law of the "Corpus Juris", including the regulations borrowed from Roman law; whereas ecclesiastical law refers to all laws made by the ecclesiastical authorities as such, including those made after the compiling of the "Corpus Juris".
In the fourth century it was applied to the ordinances of the councils, and thus contrasted with the Greek word , the ordinances of the civil authorities; the compound word "Nomocanon" was given to those collections of regulations in which the laws formulated by the two authorities on ecclesiastical matters were to be found side by side.
Considered from the point of view of its expression, canon law may be divided into several branches, so closely allied, that the terms used to designate them are often employed almost indifferently: common law and special law; universal law and particular law; general law and singular law ().
It is easy to point out the difference between them: the idea is that of a wider or a more limited scope; to be more precise, common law refers to things, universal law to territories, general law to persons; so regulations affecting only certain things, certain territories, certain classes of persons, being a restriction or an addition, constitute special, particular, or singular law, and even local or individual law.
However, the method of studying and teaching gradually developed: if the early decretalists made use of the elementary plan of the gloss and literal commentary, their successors in composing their treatises were more independent of the text; they commented on the titles, not on the chapters or the words; often they followed the titles or chapters only nominally and artificially.