Popes through the centuries have issued their most important written messages in one of 10 classic forms, ranging from encyclical to "chirograph," a brief document on a highly limited subject. But most of these are typically formulaic texts that do not express the distinctive voice or charism of the man who issues them.

Pope Francis has already published an encyclical, traditionally considered the most authoritative form of papal writing. But in the opening paragraphs of "Lumen Fidei," released in July, he explained that the text was essentially the work of his predecessor, Pope Benedict XVI, to whose words Pope Francis had merely "added a few contributions" of his own.

By contrast, Pope Francis has made clear that "Evangelii Gaudium" is very much his own work.

Apostolic exhortations are often based on deliberations of synods of bishops, and this one takes into account the October 2012 synod on the new evangelization. But last June, Pope Francis informed the ordinary council of the Synod of Bishops, which is normally responsible for helping draft post-synodal apostolic exhortations, he would not be working from their draft.

Instead, the pope said, he planned to write an "exhortation on evangelization in general and refer to the synod," in order to "take everything from the synod but put it in a wider framework."

That choice surprised some, especially since Pope Francis had voiced his strong commitment to the principle of consultation with fellow bishops and even suggested that the synod should become a permanent advisory body.

But the pope was merely reverting to earlier practice. None of the first three modern synods, in 1967, 1969 or 1971, led to a papal document. It was not until 1974 that Pope Paul first chose to use a synod's recommendations to write an apostolic exhortation, "Evangelii Nuntiandi," published the following year.

Pope Francis may already be deep into his next major document, an encyclical on social teaching. In May, Bishop Luigi Martella of Molfetta, Italy, wrote that the pope had recently told him and other bishops of Italy's Puglia region that he was planning an encyclical on poverty, "understood not in an ideological and political sense, but in an evangelical sense." The bishop said the encyclical would be called "Beati Pauperes" (Blessed Are the Poor).

Subsequent reports suggest that Pope Francis' social encyclical might deal not only with poverty but also with protection of the natural environment, a topic on which he has voiced concern from practically the start of his pontificate.

A category of document that Pope Francis has not yet produced, but in which he is likely to make a major contribution, is that of apostolic constitutions. These are usually routine legal documents establishing a new diocese or appointing a bishop. But they can also address exceptional matters, as did Pope Benedict's 2009 "Anglicanorum coetibus," which established personal prelatures for former Anglicans who join the Catholic Church.

An apostolic constitution especially relevant to this pontificate is Blessed John Paul's 1988 "Pastor Bonus," which was the last major set of changes to the church's central administration, the Roman Curia. Planning a revision of that document was the one specific task Pope Francis assigned to his advisory Council of Cardinals when he established the eight-member body in September.

Another consequential type of papal document is an apostolic letter given "motu proprio," i.e., on the pope's own initiative. Such letters are used to set up new norms, establish new bodies or reorganize existing ones. Pope Benedict issued 18 of them in the course of his eight-year pontificate -- most famously in 2007, when he lifted most restrictions on celebration of the Tridentine Mass; and most recently in February, when he changed the voting rules of a papal conclave less than a week before he resigned from office.

Pope Francis has already issued three such apostolic letters in his first eight months: to update the Vatican's criminal code so that it includes all Vatican employees around the world, not just those working in Vatican City; to broaden Vatican City laws against money laundering and terrorism financing so that they cover all the offices of the Roman Curia; and to expand the reach of the Vatican body that inspects suspicious financial transactions.

As evidence of the pope's determination to reform, these impersonal legal documents may be his most eloquent statements yet.