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Anno Domini, Ad Infinitum, and Aqua Pura: Translating Latin Phrases as a Grammatical Exercise

By John Garger

Anno Domini, ad infinitum, and aqua pura are three common Latin phrases used in English. Learn about the literal and figurative translation of each.

One of the most influential languages, Latin continues to bombard our daily lives in the many Latin phrases we take for granted. Using these phrases as models for proper Latin grammar, the Latin student can focus his/her attention on the structure of Latin without the complication of translating long, cumbersome sentences from Latin to English.

Anno Domini

Anno Domini, sometimes abbreviated AD or A.D., is a Latin phrase used to indicate dates of the Julian and Gregorian calendars. This designation is indicative of the time after the birth of Jesus Christ in contrast to dates before His birth which are designated with BC or B.C..

Anno Domini can be literally translated as “in the year of the Lord” but is often mistranslated as “in the year of our Lord.” “Anno” is an excellent example of the use of the “ablative of time when or within which.” This construction is used to indicate when something takes place. Unlike other ablative constructions (but similar to the ablative of means or instrument) the ablative of time when does not use a preposition such as “in”, “at”, or “within.” These words must be appropriately supplied when translating from Latin to English. A literal translation of “Anno” in this case can be “in the year.”

“Domini” is simply the genitive form of the word “Dominus” and is used in this case to indicate possession, or to whom the year (Anno) belongs. Recall that the genitive is often used to indicate possession. Therefore, “Anno Domini” may be properly translated as “in the year of the Lord.”

Ad Infinitum

Ad Infinitum is a phrase that literally translates as “to infinity” but is colloquially translated to mean “forever”, “ongoing”, or sometimes even “to the horizon” (a metaphor for "forever"). Ad Infinitum is an excellent example of the use of the accusative of place to which. This construction is formed with a preposition plus the accusative case making it easier to recognize than constructions that do not use a preposition.

“Ad” is a Latin word which may be translated as “to” in contrast to “ab” (or just “a” when followed by a consonant) which means “from.” “Infinitum” is the accusative form of the word “infinitus” meaning “infinite”, “unbounded”, or “endless.” Do not confuse this form of the word with the neuter form, which is also “infinitum” in both the nominative and accusative cases. Together “ad” and “Infinitum” may be translated as “to infinity.” Notice that the accusative of place to which need not refer to any particular place but can be used to indicate a theoretical place or destination such as infinity.

Aqua Pura

Even non-Latin students can understand this phrase as meaning “pure water” since the word “pura” is similar to English’s “pure” and aqua (similar to Spanish’s agua) is related to the English word “aquarium.” Simple as it may be, this phrase does illustrate two important grammatical constructions.

First, notice that the adjective “pura” follows the noun it modifies, “aqua.” This is common in Latin because the noun is considered more important that any word that may modify it. Essentially, the Romans would say “water pure” rather than English’s “pure water.” This is common throughout Latin so always be on the lookout for adjectives that follow nouns, a practice unfamiliar to native English speakers. As a side note, speakers of Romance languages do not have this problem as English speakers have. Many of the languages derived from Latin continue to place the adjective after the noun it modifies. Therefore, it is especially more difficult for English speakers to remember this common Latin construction.

Second, notice that the adjective “pura” agrees with the noun it modifies, “aqua”, in case (nominative), number (singular), and gender (feminine). Since “aqua” is a feminine noun, “pura” is also in its feminine form. As an adjective, “pura” has masculine, feminine, and neuter forms. For example:

Vir purus (the pure man)

Femina pura (the pure woman)

Flumen purum (the pure river)

In this case, “aqua” and “pura” have similar forms but this is not always the case with nouns and adjectives as illustrated in the three examples above. Notice that “vir purus” and “flumen purum” do not have similar forms even though the adjective “purus –a –um” agrees with the nouns it modifies in case, number, and gender.


The ablative of time when found in the phrase “Anno Domini” can be difficult to spot because its construction lacks a preposition. This is one example of how Latin’s efficiency plays havoc with the English speaker’s sense of grammar. One way to combat this is to remember to look for the ablative case whenever words dealing with time appear or whenever a Latin sentence is discussing something in sequence. In contrast, the accusative of place to which found in “Ad Infinitum” does employ a preposition, so be aware that prepositions followed by the accusative case may indicate this construction. Finally, the simple construction implied by “Aqua Pura” is a good, albeit simple, lesson in noun-adjective agreement. Be aware, however, that adjectives must agree in case, number, and gender of the nouns they modify but they do not need to agree in form.