What differentiates a priest, a clerk, a capellanus, a subdeacon and a rector?

Before getting into what is the differences between a priest, a clerk, a subdeacon, a rector and a capellanus, it is important to understand that a priest may not only function as a priest, but also as a capellanus, a rector and under certain circumstances are called clerks also.

What is a priest?

A priest is an ordained minister in the Catholic Church who's functions include the administration of the sacraments within in a diocese or Religious Order.

Priest

This word (etymologically "elder", from presbyteros , presbyter ) has taken the meaning of "sacerdos", from which no substantive has been formed in various modern languages (English, French, German). The priest is the minister of Divine worship, and especially of the highest act of worship, sacrifice...

What is a rector?

Rector

Priests who preside over missions or quasi-parishes are called rectors: in England and the United States they are removable and irremovable, or permanent. These latter are known also as missionary rectors (M.R.). The term rector is applied likewise to the heads of universities, seminaries, and colleges; to the local superiors of religious houses of men; to the pope, as rector of the world, in the conferring of the tiara...

What is a subdeacon?

Subdeacon

The subdiaconate is the lowest of the sacred or major orders in the Latin Church. It is defined as the power by which one ordained as a subdeacon may carry the chalice with wine to the altar, prepare the necessaries for the Eucharist, and read the Epistles before the people (Ferraris, op. cit., infra No. 40).

The Order of Subdeacons was suppressed by Pope Paul VI, but the faithful who follow the Tridentine Rite still have subdeacons. The Major Orders are to be understood as priest, deacon and subdeacon.

What is a clerk?

Clerks Regular

By clerks regular are meant those bodies of men in the Church who by the very nature of their institute unite the perfection of the religious state to the priestly office, i.e. who while being essentially clerics, devoted to the exercise of the ministry in preaching, the administration of the sacraments, the education of youth, and other spiritual and corporal works of mercy, are at the same time religious in the strictest sense of the word, professing solemn vows, and living a community life according to a rule solemnly approved of by the sovereign pontiff.

Cleric

A person who has been legitimately received into the ranks of the clergy. By clergy in the strict sense is meant the entire ecclesiastical hierarchy. Consequently a cleric is one who belongs in some sense to the hierarchy.

In former days clerics were composed of priests, deacons, subdeacon, acolyte, exorcist, lector and porter. The latter four were known as the Minor Orders.

What is a capellanus?

Capellanus is a term that was used to define the office of a chaplain.

There are many types of chaplains in the service of the Church and the above link can give you some basic information on the differences between them. Chaplains normally are ordained priests.

• Court chaplains
• Beneficed chaplains
• Regulations concerning beneficed chaplains
• Parochial or auxiliary chaplains
• Domestic chaplains
• Chaplains of convents
• Pontifical chaplains
• Military chaplains

As for your ecclesiastical abbreviations:

• B.A. — Baccalaureus Artium ("Bachelor of Arts")
• M.A. — Magister Artium ("Master of Arts")
• B.D. — Bachelor of Divinity
• A.M. — Artium Magister ("Master of Arts")

I'm no expert, but will attempt a partial answer - first, the educational qualifications refer to:-

BA - Bachelor of Arts

MA - Master of Arts (traditionally awarded automatically to Oxford graduates one year after graduating)

BD - Bachelor of Divinity

AM - I think another description on of MA.

A clerk would probably refer to a clerk in holy orders - there were many grades of holy orders, most men at Oxford or Cambridge would be in minor orders.

A priest is a generic term for a man (prior to modern times) who had been ordained priest by a Bishop. Only a priest could absolve sins, or consecrate the bread and wine at Mass.

A subdeacon was, I think the lowest form of holy orders, originally to assist the deacon and serve at Mass.

A rector is somewhat different. Parish priests were entitled to tithes - one tenth of the parish produce. These were divided into greater and lesser tithes - a rector received the greater tithes and was effectively the owner of the living. (A vicar was appointed by a rector and, I think, received only the lesser tithes or a stipend.)

A capellanus is a chaplain - either employed by a great family or paid to say Masses, for example, for the souls of the dead.

I think you really need to consult a good local history manual, medieval/early modern church law and practice were pretty complicated!

Edit The **rector* of a parish is, essentially, the owner - the one entitled to the great tithes and to appointing the priest. The rector may be the priest, but - pre-Reformation - could well be a monastery, university, prelate or other. Post-Reformation, rectors were often the largest landowner locally, or indeed some distant noble. S/he could obviously not act as priest, not being ordained, but were said to have the gift of the living - eg could appoint a vicar (priest) as a form of patronage. In the Anglican Church, lay patrons still exist, and can offer a candidate for a parish, subject to the Bishop's approval.