Some Frequently Asked Questions and Answers to Them

About Nouns

What does declension mean?

Declension is a term indicating a class, or family group, to which nouns (and adjectives) belong. If you know the declension, you know how to spell the endings. Declension has no other significance for Latin nouns; declension does not affect meaning. The declension of a noun does not signify gender (masculine, feminine, or neuter), even though most first declension nouns are feminine and most second declension nouns are masculine or neuter. See below for adjectives.

How can I tell what declension a noun is?

To tell the declension of a noun, look at the whole vocabulary (or dictionary) entry, which will show how the noun looks in the nominative singular, and in the genitive singular, and will tell you the gender of the noun.
Examples:

agricola, agricolae, m. [means farmer]
The genitive, the second form given, ends in -ae. Therefore the noun is first declension. Its gender is masculine.
rosa, rosae, f. [means rose (the flower)]
The genitive ends in -ae. Therefore the noun is first declension. Its gender is feminine.

latus, lateris, n. [means side or flank]
The genitive, the second form given, ends in -is. Therefore the noun is third declension. Its gender is neuter.
pomus, pomi, f. [means fruit tree]
The genitive ends in -i. Therefore the noun is second declension. Its gender is feminine.
boletus, boleti, m. [means mushroom] The genitive ends in -i. Therefore the noun is second declension. Its gender is masculine.
ager, agri, m. [means field]
The genitive ends in -i. Therefore the noun is second declension. Its gender is masculine.
fructus, fructus, m. [means fruit]
The genitive ends in -us. Therefore the noun is fourth declension. Its gender is masculine (most, but not all, fourth declension nouns are masculine).

How can I tell what form of the noun to put the endings on?

The form of the noun to which one attaches the endings, each of which indicates the noun's function within a sentence, is not often apparent from looking at the nominative singular, the first part of the vocabulary entry. While it is useful to know the nominative in order to spell the word properly when it is the subject of a sentence, it is nice to know how to spell the other cases properly as well.
RULE: take the letter or letters which indicate genitive case away from the second form of the word given, and you will have the word's root (aka stem). In the examples above, the stem of agricola is agricol-; the stem of rosa is ros-; the stem of latus is later-; the stem of pomus is pom-; the stem of boletus is bolet-; the stem of ager is agr-; the stem of fructus is fruct-. If the stem of the word appears in English words derived from Latin, thinking of a related English word can help you remember the Latin stem. Examples include lateral (from latus, stem later-), agriculture (from ager, stem agr-).

About Adjectives

What does declension mean with respect to adjectives? The same as for nouns?

Declension, as for nouns, is a term indicating a class, or family group, to which nouns and adjectives belong. If you know the declension, you know how to spell the endings. Declension does not affect meaning. The declension of an adjective signifies both how to spell the endings and the gender (masculine, feminine, or neuter) of the specific form of the adjective.

How can I tell what declension an adjective is?

To tell the declension of an adjective, look at the whole vocabulary (or dictionary) entry, which will show how the adjective looks in the nominative singular, and will show separate forms for masculine, feminine, and neuter (in that order), if the adjective has separate forms. There are only three declensions of adjectives, used in two groups. One group is the first-and-second-declension-adjective family, the other is third-declension-adjective family. First-and-second-declension adjectives have separate endings for masculine, feminine, and neuter; occasionally the masculine nominative singular form does not display the adjective's stem, but the feminine form always does. Third declension adjectives usually have only two forms, one for both masculine and feminine, the other for neuter. Occasionally third-declension adjectives have only one form for all three grammatical genders.
Examples of first-and-second-declension adjectives:

magnus magna magnum (usually written magnus -a -um) [means large or great]
pulcher pulchra pulchrum (written pulcher -chra -chrum to show the stem) [means beautiful]
pauci paucae pauca [means few; since the adjective's meaning is plural, it does not exist in singular forms]

Examples of third-declension adjectives:

omnis omne (usually written omnis -e) [means all, every]
tenax tenacis (written tenax -acis) [means holding fast, tenacious] and potens, potentis [means powerful] are adjectives which have only one form no matter what their gender; for adjectives such as these the dictionary entry will give the genitive singular so that you can see what the stem is (tenac- and potent-, respectively).

How do you figure out which form of adjective to use?

The first thing to decide is the meaning the adjective has to have: if you want to say "large fruit tree" you want to use magnus -a -um for "large". Since "fruit tree" is a feminine noun (see above), even though it is second declension, you must use the feminine form of magnus -a -um, which is magna. A large fruit tree is magna pomus. The ending of the noun and adjective do not have to rhyme with each other; in fact, it often sounds better if they do not. You can use nouns from any declension with adjectives of any other declension. Adjectives do not change their declensions in order to match the nouns they are used with. If you want to say "every fruit tree" that is omnis pomus. "Tenacious fruit tree" is pomus tenax.

About Verbs

What are principal parts?

Q&D answer: The forms (usually 4) of the verb as it appears in vocabulary list.
More useful answer: Each verb - if it is not irregular or defective or deponent - has four 'parts' given for it. These parts enable you to identify the verb completely and spell all of its forms. The first part shows the first person singular present active indicative; the second is the present active infinitive; the third is the first person singular perfect active indicative; the fourth is the perfect passive participle.

The second principal part tells you what conjugation the verb is. Knowing this, and knowing the first principal part, you can spell all of the forms (once you learn the endings) of the present, imperfect, and future indicative, the present and imperfect subjunctive, the imperative, and the present active participle (the one that ends -ing in English, as in "running", "thinking"). Verbs which are not defective or deponent have a present infinitive (second principal part) ending in -re. The vowel preceding these last two letters identifies the conjugation, long a for first conjugation, long e for second, short e for third, and long i for fourth. The first person singular (first principal part) sometimes enables you to guess what the infinitive will look like but this method is only reliable for second conjugation verbs.

The third principal part is the perfect active indicative. Knowing this you can form the perfect, pluperfect, and future perfect indicative, the perfect infinitive, and the perfect and pluperfect subjunctive.

The fourth principal part is the perfect passive participle. You use this form in a variety of ways, but as a verb, you need it to make the perfect, pluperfect, and future passive indicative and the perfect and pluperfective passive subjunctive.