How to Form the Fourth Declension in Latin

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Since Latin is an inflected language, word endings change to indicate their function in the sentence. Usually, these forms follow patters to aid the student in recognizing and properly translating the word. However, there are so many exceptions in Latin that the patterns can not be relied on, leaving the students with no choice but to memorize the forms of different words. In addition, the gender of each word must be memorized for the same reason.

The fourth declension gives students a bit of a reprieve from previous declensions because far fewer words belong to the fourth declension in comparison to the previous three. Most fourth declension nouns are masculine but there are some feminine words with identical endings, just as the masculine and feminine of the third declension have similar forms. However, this does not preclude the need to memorize the gender of every word. Failure to do so makes it much more difficult for students when they try to translate Latin nouns in a sentence.

Fourth Declension Forms – Masculine and Feminine

Fourth declension nouns have a characteristic –us ending in the nominative singular which is similar to the ending of second declension masculine nouns. This fact illustrates the necessity to memorize the genitive form of every noun so its declension may be immediately known. As with previous declensions, fourth declension nouns are formed by adding endings to the stem of the word. For example:


nom. fructus

gen. fructus

dat. fructui

acc. fructum

abl. fructu


nom. fructus

gen. fructuum

dat. fructibus

acc. fructus

abl. fructibus

One issue that gives students problems with the fourth declension is the similar forms for the nominative and genitive singular and the nominative and accusative plural; each has the form fructus. Although the –us in the nominative singular is short and long in the other cases, no help is given when Latin text is given without the helpful macrons shown in many textbooks. Other than this issue, no other forms of the declension should give trouble beyond what has been learned in previous declensions.

Fourth Declension Forms – Neuter

Of the five declensions, the third declension neuter forms are the strangest. The signature –u is used for the ending in the neuter gender in four of the five singular cases. Other than this anomaly, the plural forms of the cases are quite similar to neuter forms found in other declensions. Neuter third declension nouns are declined as follows:


nom. cornu

gen. cornus

dat. cornu

acc. cornu

abl. cornu


nom. cornua

gen. cornuum

dat. cornibus

acc. cornua

abl. cornibus

Notice the –uum ending of the genitive plural is similar to other declensions except two u’s are used instead of one. Also notice the –ibus ending for the dative and accusative plural just like the third declension. In fact, the signature –u– of the fourth declension changes to an –i– exactly like a third declension noun. Also, the typical –a of neuter nouns is present in the nominative and accusative plural.


The fourth declension has a few quirks but these are minor to students of Latin by the time they reach this experience level with Latin declensions. The forms of masculine and feminine nouns are similar, just as they are in the third declension. The forms of the neuter should be no problem as students enter the intermediate stages of elementary Latin. Luckily, far fewer Latin words are found in the fourth declension in comparison to the previous three. However, some key words such as manus (hand), senatus (senate), and domus (house) are common enough to make the fourth declension an important part of elementary Latin study.

This post is part of the series: Latin Declensions

Since Latin is an inflected language, the endings of its words change to indicate their function in a sentence. Latin nouns and adjectives are declined into five basic cases. These nouns and adjectives belong to one of five declensions, each with its own set of rules and forms.

  1. How to Decline First Declension Latin Nouns
  2. A Primer on Latin’s Second Declension
  3. Learn How to Form Third Declension Latin Nouns
  4. Latin Declensions: Fourth Declension
  5. How to Decline Latin Words of the Fifth Declension