Final answer:
All forms in the third declension paradigm in Latin are derived from the stem rather than the nominative singular. This is because the stem provides a consistent base for conjugating the various cases, as opposed to the often variable nominative singular form.
Step-by-step explanation:
All forms in the third declension paradigm are derived from the stem, not the nominative singular. In Latin, the third declension includes a wide variety of words with a diverse set of endings in the nominative singular, which is why the stem, usually found by looking at the genitive singular form, is used to form all other cases. For example, the word 'rex' (king), which is irregular, has a nominative singular form that looks very different from the other forms; but for a regular third-declension word like 'lupus' (wolf), the stem 'lup-' is consistent throughout.