According to Jeffrey L. Singman, in his book on the Middle Ages, there are several differences between “monks” and “friars.”
The way Singman tells it, the only TRUE monks are the Benedictines, an order which was started by Saint Benedict of Nursia (Italy) in the 500s. Originally, these monks led an ascetic life dedicated to communal worship, and full of honest, physical toil.
The origin of the word “monk” is “mono”– meaning “one.” Although Singman does not state this outright, I came away with the impression that before Benedict had the idea that “Hey, we should all be alone together!”— that monks went about their spiritual quest mostly in a solitary fashion.
Over time, the Benedictine monks slowly moved away from their ascetic life and became, in some places, quite wealthy. In fact, Singman tells us that monasteries (the places where monks live) began to depend more and more on the incomes they received from rich landowners who, at their deaths, bequeathed the monasteries property– sometimes vast and profitable domains. It was not uncommon at all for a fair-sized monastery to receive incomes from multiple, bequeathed manors– “manors” being the land-holdings (including the serfs who worked the land) of a knight or lower-level nobleman .
Singman writes that, by the middle of the Middle Ages, most monks were not poor at all, but were largely composed of the non-firstborn sons of the aristocracy (the aristocracy comprising about one-percent of the population of the Middle Ages).
Eventually, monasteries began to develop a bad reputation as places where men-of-God were living the high life at the expense of the tithing masses and those rich men duped into leaving a monastery their properties at their deaths.
It was almost assuredly in reaction to the perceived moral decline of the monasteries that other religious orders sprang up in the 1200s. Singman writes that Saint Francis started the Franciscans in 1210, and that Saint Dominic founded the Dominicans in 1216. Singman designates the members of these two new religious orders– not as monks– but as “friars.” Unlike many of the Benedictine monks, friars took their vows of chastity and poverty seriously.
Friars, like monks, dedicate their lives to the pursuit of spiritual goals, but Singman tells us that Friars come at it from a different angle. Whereas the Benedictine monks pursued their own personal enlightenment and greater godliness, the new friars took it upon themselves to minister to the world. Monks withdrew from society, but friars attempted to improve society through their community outreach. Benedictines could collectively own vast holdings, but Franciscans and Dominicans were truly supposed to hold no– or very little– property or wealth, even collectively. And whereas monks were typically from the aristocracy, friars were frequently drawn from moderately well-off city-folk.
All three religious orders (Benedictine monks, Franciscan friars, and Dominican friars) are different from “priests”– as it is the vocation of priests to act as intermediaries between Man and God. Although the religious orders are certainly under the authority of the Pope (all these orders are, perhaps not so obviously, Catholic organizations), priests are more directly implanted in the church hierarchy. That hierarchy has remained virtually the same for centuries, and flows down from the Pope to the Archbishops to the Bishops (who are assisted by Canons). Beneath the Bishops come the Parish Priests. A Bishop might oversee hundreds of Priests, whereas an Archbishop would tend a flock of only a dozen or less Bishops. All the positions of Bishop and higher are known as the “Regular” Clergy, and those below Bishops are the “Secular” Clergy. There was a time when all of the Regular Clergy positions were filled only by men drawn from the monasteries (thus, the name “Regular” Clergy, from the Latin “regula” or “rule”– as in the monks lived a life –at least supposedly– according to strict rules).
There came to be rivalries between the various religious orders over time, and sometimes disputes over religious matters would pit the orders against each other, similar to how ideological disputes today tend to divide along the lines of political-party affiliation.
Lastly, many friars– especially the Dominicans– acquired reputations as superior scholars. Both Thomas Aquinas and Roger Bacon were friars (Aquinas was a Dominican, and Bacon a Franciscan).