Thus far we have learned second declension nouns, which have a stem ending in omicron, and first declension nouns, which have a stem ending in either alpha or eta. Third declension nouns have stems that end in a consonant. When the endings are added, the consonant will go through various predictable transformations.
Unlike the first and second declensions, which build their forms from the nominative, third declension nouns will be built from the genitive. Thus, in the third declension, you must be aware of the genitive form of the noun.
To find the stem of third declension nouns, take the oj off the genitive form.
The following consonants in the voiced and unvoiced columns are called “stops” because of the way the air flow stops when pronouncing them. The aspirates are fricatives. These letters will be transformed when the sigma ending of the third declension is added. (Mounce, Basics, 78)
The consonants (labials, velars, dentals) change in the following ways when the sigma ending is added. The two letters contract into one. In the case of the dentals the dental is dropped.
Labials: p, b, or f + s = y
Velar: k, g, or x + s = c (sa Dentals: t, d, or q + s = s (e]lpiNu drops out when followed by a sigma (Dat. Pl.).
We will learn four paradigms that are typical of third declension nouns. The adjective pa?j, pa?sa, pa?n (each, all) will be examined as a 3-1-3 adjective (third-first-third declension).
Take the oj ending off the genitive form to find the stem. In the nominative singular a sigma is added to the stem, causing the final consonant of the stem to change. Because this declension is so different and occurs so frequently, it is good to learn how to chant through the xa Third Declension Endings