When I was first introduced to the third declension I thought I had entered Spartan boot camp. I had just started to grasp the definite article and case endings for nouns (1 and 2 declension) and it seemed like everything I had learned was turned upside down. After working with them for a few weeks they no longer seem so terrible, though still a bit weird.

The Greek declension rules are: [1]

• stems ending in α or η are first declension
• stems ending in ο are second declension
• stems ending in consonants are third declension

The first and second declension case endings follow the definite article with very few exceptions. The third declension however has a different set of case endings.

The declension system is a modern way of organizing case endings. It was not something first century Greek students would have used to learn the language.

It is only since the seventeenth century A.D. that modern grammarians distinguish for convenience three declensions in Greek. The older grammars had ten or more. […] Evidently therefore the ancient Greeks did not have the benefit of our modern theories and rules, but inflected the substantives according to principles not now known to us. The various dialects exercised great freedom also and exhibited independent development at many points, not to mention the changes in time in each dialect. The threefold division is purely a convenience, […] [2]

The third declension nouns use the same definite article as the first and second declension nouns. Therefore the feminine third declension noun in the accusative singular would be:

τnv ἐλπιδα

Like all nouns, the entry in the lexicon for a third declension noun is listed using the nominative singular form. The entry also provides the same information (as shown below for the word hope):

The definite article ἡ, let’s us know that the gender of this noun is feminine.

For the third declension nouns we derive the stem by dropping the letters ος off the genitive case ending:

ἐλπιδ

It is usually difficult to determine the stem from the nominative case ending since the consonant often changes with the sigma case ending as it does here (the delta drops off per the square of stops).

ἐλπιd + ς = ἐλπις

Using the information from the lexicon we can decline the word as a 3rd declension feminine noun as follows:

Our professor has stressed the importance of memorizing the full lexical entry of each noun so that we are able to determine the stem, gender, and declension. And that still seems like an exercise straight out of Sparta.

[1] Noun rules and case endings are based on Mounce’s Basics of Biblical Greek 2nd edition
[2] Robertson, Grammar of the Greek NT 3rd Edition page 247