The 'consonant-stem' and 'i-stem' declension. This declension contains nouns that are masculine, feminine, and neuter. The stem ends in the root consonant, except in the special case where it ends in -i (i-stem declension). The i-stem, which is a vowel-stem, partially fused with the consonant-stem in the pre-Latin period and went further in Old Latin. I/y and u/w can be treated either as consonants or as vowels; hence their classification as semi-vowels. Mixed-stem declensions are partly like consonant-stem and partly like i-stem. Consonant-stem declensions vary slightly depending on which consonant is root-final: stop-, r-, n-, s-, etc. The paradigms below include a stop-stem (reg-) and an i-stem (igni-).