Learn Latin Legal Terms 'Compos Mentis' and 'Ceteris Paribus'

Learn Latin Legal Terms 'Compos Mentis' and 'Ceteris Paribus'
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Latin may be a dead language but its influences live on in the many phrases used in English. Law is perhaps the profession most impacted by Latin since modern law was first practiced during Latin’s Medieval Period. However, many of the Latin phrases used by English speakers are commonly translated metaphorically, not literally.

As an exercise in translation, Latin students gain a practical perspective on the use of Latin. Latin phrases often exemplify the grammatical constructions used in Classical as well as other periods in Latin’s history. The two Latin phrases discussed here introduce students of law and Latin to the common nominative-genitive pairing and the ablative absolute.

Translating Compos Mentis from Latin to English

Most legal systems require that persons entering into a contract, writing a will, or standing trial for a crime be mentally fit to do so. This means the person must be capable of reasonable decision-making and have the ability to contemplate and comprehend the consequences of his/her actions. We have all heard the famous phrase often associated with the writing of a will that starts, “I, , being of sound mind…” This phrase is the will writer’s way of indicating that the decisions he/she has made in the will were made at a time when the consequences of decisions were well-known and acceptable to the writer.

Compos mentis is the phrase used to indicate that someone is “of sound mind.” Compos is the nominative form of the word “compos” which literally means “having control,” “in possession,” or “sharing.” As a third declension adjective, its genitive form changes to “compotis” and then declines as any other third declension adjective.

Mentis is the singular genitive form of the third-declension noun “mens” meaning “mind,” “thought,” or “intention.” As its genitive form suggests, it is indeed where English gets the word “mental.” Recall that the genitive case is the case of possession indicating to whom something or someone belongs.

Taken together, compos mentis can be literally translated as “having control of [one’s] mind.” Notice that this is quite different from the popular translation “being of sound mind.” This phrase is a good example of the common nominative-genitive pairing often found in Latin phrases.

A Translation of Ceteris Paribus from Latin to English

Commonly translated as “all things being equal,” legal and scientific communities use ceteris paribus to indicate a theoretical or hypothetical situation. In science, researchers may wish to control certain variables to isolate the relationship between two variables under study. These researchers may use to term ceteris paribus to indicate that a relationship is true barring any unforeseen or uncontrollable variables. The same can be said of the legal profession when a lawmaker may ask, “ceteris paribus, can we expect that a citizen of this country is aware of that law.”

Ceteris is the ablative plural form of the word “ceterus” which literally means “the other” or “the rest.” It may help to note that ceterus is the source of the phrase et cetera (often abbreviated etc.) which means “and the others.” The fact that ceteris is in its ablative plural form becomes significant when we explore the form of the word paribus.

Paribus is the ablative plural form of the word “par” which can be literally translated as “equal. However, par should not be confused with the similar word “pars” (genitive “partis”) which means “part” or “piece.” Par is related to the English word used in the game of golf to indicate that one has sunk one’s ball in the recommended number of strokes. Doing so means one is “on par” with the course. “Par,” therefore, means “equal” or “proper.” For a literal translation, “[with] the others equal” is a reasonable approximation.

Taken together with both words of the phrase in the ablative case, ceteris paribus is an excellent example of the ablative absolute. In Latin, the ablative absolute is a phrase “loosened” or “separated” from a sentence and is often removed from a sentence’s main clause by commas. Normally, the ablative absolute indicates some situation or circumstance that describes or clarifies the action in the remainder of the sentence. Take for example:

Ceteris paribus, a man will choose love over death.

Notice that the phrase “ceteris paribus” clarifies a man’s decision to choose love over death. The Latin phrase indicates that if other variables are held constant, love is preferable to death.


Over the course of Latin’s history, ancient and recent Latin phrases are often translated loosely from their literal translations. Quite often, participles are added in translation where they don’t exist in the original phrase. Often, users of the phrase such as legal professionals are unaware that the translations they assume or take for granted are poor approximations of the phrase’s literal meaning. Again, exploration of these phrases is an excellent exercise for the Latin student.