Lesson 14. Of Nouns: Fifth Declension

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We now come to the Fifth and final Declension of nouns. By this point, we have already learned how to recognize and decline the First, Second, Third, and Fourth Declensions, and we have learned to rely on one steady principle that has never failed us: a noun’s declension is known by its Genitive singular ending. That principle remains fully in force here, and if we keep it firmly in mind, the Fifth Declension will be the easiest of all.

We recall what we already know. A Genitive singular ending in -ae (or -es when the Nominative ends in -e) marks the First Declension. A Genitive singular ending in -i marks the Second Declension. A Genitive singular ending in -is marks the Third Declension. A Genitive singular ending in -us marks the Fourth Declension. Now we add the Fifth Declension, which is marked by a Genitive singular ending in -ei. This ending is the defining sign. If we see -ei in the Genitive singular, we are dealing with a Fifth Declension noun.

At first glance, Fifth Declension nouns appear very simple. They have only one possible Nominative ending, which is -es. That simplicity is welcome after the variety of the Third Declension. Yet we must be careful not to let appearances mislead us. A noun ending in -es is not automatically a Fifth Declension noun. We have already seen nouns such as Anchises, which end in -es but belong to the First Declension. Once again, the Nominative alone cannot be trusted. Only the Genitive singular tells us the truth. When the Genitive singular ends in -ei, the noun belongs to the Fifth Declension.

We must also be attentive not to confuse Fifth Declension nouns with Second Declension nouns. When we see a form like rei, we might be tempted to think that the ending is -i, but it is not. The ending is -ei, and that difference matters. With practice, our eye will learn to see the difference immediately, but in the beginning we must slow down and be deliberate.

As before, vocabulary study plays a central role. The Latin dictionary gives us exactly the information we need: the Nominative singular, the Genitive singular, the gender, and the meaning. From this we identify both the declension and the stem. When we see dominus, domini, we know at once that the noun is Second Declension. When we see spiritus, spiritus, we know that the noun is Fourth Declension. When we see dies, diei, we know that the noun is Fifth Declension. The dictionary is not an optional aid; it is the means by which certainty replaces guesswork.

As with the other declensions, we continue to keep substantives and adjectives together in our thinking. When an adjective is used with a substantive, the two must agree in gender, number, and case. For example, when we say dies apricus, meaning “a sunny day,” the noun dies belongs to the Fifth Declension, while the adjective apricus follows the pattern of the Second Declension. Even though the forms come from different declensions, the agreement is exact. Thus we say diei aprici for “of a sunny day,” and a die aprico for “from a sunny day.” Likewise, when we say res facilis, meaning “an easy thing,” we say rei facilis for “of an easy thing.” In the plural we say res faciles for “easy things,” and rebus facilibus for “to easy things.” By this point, the principle of agreement should feel familiar, even when the outward forms differ.

Now we place the Fifth Declension forms clearly before ourselves by declining its chief example noun, dies, meaning “day.” In the singular number we say dies as the subject. The Genitive singular is diei, meaning “of a day.” The Dative singular is also diei, meaning “to a day.” The Accusative singular is diem, meaning “a day” as a direct object. The Vocative singular is O dies, and the Ablative singular is a die, meaning “from a day.” In the plural number we say dies as the subject, dierum for “of days,” diebus for “to days,” dies as the direct object, O dies in direct address, and a diebus for “from days.” When we say these forms carefully and repeatedly, the pattern becomes fixed and easy to recall.

There is one important note to keep in mind concerning gender. All Fifth Declension nouns are feminine, with two exceptions: dies meaning “day,” and meridies meaning “midday.” These two nouns are masculine. This is not something to reason out; it is something to remember. Once remembered, it causes no difficulty.

If we now step back and look at the Fifth Declension as a whole, we see that it is small, regular, and distinct. It is identified by a Genitive singular ending in -ei. Its Nominative singular always ends in -es. Its Accusative singular ends in -em, and its plural forms are built with -erum in the Genitive and -ebus in the Dative and Ablative. Compared to the Third Declension, this is a narrow and orderly system.

With this lesson, we have now encountered all five noun declensions. Each has its own character, but all are governed by the same principles we have been practicing from the beginning: identify the declension by the Genitive singular, form the stem from that Genitive, apply the proper endings, and make adjectives agree faithfully with substantives. What remains is not new theory, but review and strengthening, so that these forms become part of our working knowledge rather than something we must stop and puzzle out each time.

Memory Work

1. How many different terminations are found in the Nominative case of the Fifth Declension?
Only one: -es.

2. Decline the Fifth Declension noun hic Dies. (State the case name, the Latin form and the English.)
Singulariter: Nominativo, hic Dies, a Day; Genitivo, Diei, of a Day; Dativo, Diei, to a Day; Accusativo, Diem, a Day; Vocativo, O Dies, O Day; Ablativo, a Die, from a Day. Pluraliter: Nominativo, Dies, Days; Genitivo, Dierum, of Days; Dativo, Diebus, to Days; Accusativo, Dies, the Days; Vocativo, O Dies, O Days; Ablativo, a Diebus, from Days.

In short: Dies, Diei, Diei | Diem, O Dies, a Die | Dies, Dierum, Diebus | Dies, O Dies, a Diebus.

Note: All nouns of the Fifth Declension are of the feminine gender, except for Dies (Day) and Meridies (Midday).

3. Summary of the Fifth Declension:

Note: Neuter nouns of the Fourth Declension have all singular endings in -u.

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