Understanding the -ix, -ices, and -ice Suffixes

I have been struggling with the morphology of the plural of -ix nouns including feminine -trix nouns. Some examples include appendix~appendices, matrix~matrices, helix~helices, animatrix~animatrices, janitrix~janitrices, and sculptrix~sculptrices. Sometimes another suffix or connecting vowel attaches to the oblique form as in appendicitis, matriculate, helicoid, and helicopter. My specific struggle was with the plural of the feminine agent nouns like animatrices, janitrices, and sculptrices.

Recently I had been studying the third declension of Latin and Ancient Greek. Third declension nouns and adjectives end in -is in Latin and -os in Ancient Greek in the genitive singular. Many third declension words have a different oblique stem than the nominative singular. The oblique stems are the older forms, preserving the historical origin, while the nominative singular underwent various changes. For example, the oblique stem of Latin genus (genitive generis) is gener- and of Ancient Greek stóma (genitive stómatos) is stómat-. The bases <Gene>, <Gener>, <Stome>, and <Stomate> developed from genus, generis, stóma, and stómatos. For many classical third declension words, English developed two separate but related bases.

Some third declension Latin nouns end in -ex in the nominative singular and have -ic- oblique stems. (Note that the -ex is a noun ending, not a suffix. The distinction between ending and suffix matters in classical languages.) For example, English borrowed the words caudex, codex, index, vertex, and vortex from Latin caudex, cōdex, index, vertex, and vortex. All five Latin words are third declension nouns whose nominative singular stem differs from the oblique stem. The oblique stem of caudex (genitive caudicis) is caudic-, of cōdex (genitive cōdicis) is cōdic-, of index (genitive indicis) is indic-, of vertex (genitive verticis) is vertic-, and of vortex (genitive vorticis) is vortic-. The nominative singular noun ending -ex attaches to the caud-, cōd-, ind-, vert-, and vort- stem while the other endings such as the plural –es and genitive singular -is attach to the oblique stem. English then developed two separate but related bases from the nominative singular and oblique stems: <Caud>, <Caudice>, <Code>, <Codice>, <D>, <Dice>, <Vert>, <Vertice>, <Vort>, and <Vortice>. English also developed the singular -ex suffix and the plural -es suffix from the Latin -ex and -es noun endings. (Note that the Latin plural -es suffix is different from the English plural -es suffix despite both forming plural nouns.)

Returning to the singular and plural of -ix words, I could see similarities between the singular -ix and plural -ices and the singular -ex nouns with -ic- oblique stems. Just as the plural of codex is codices, the plural of matrix is matrices. But I also had to account for the fact that the -ix attaches to either a base or the -(o)r suffix (and rarely the unrebracketed Latin -t(o)r suffix). For example:

appendix ~ appendices ~ appendicitis
helix ~ helices ~ helicopter
matrix ~ matrices ~ matriculate
radix ~ radices ~ radical
animator ~ animatrix ~ animatrices
janitor ~ janitrix ~ janitrices

The answer finally dawned on me when I realized that the -ix is a Latin suffix, not a noun ending. An ending is an inflectional morpheme that marks grammatical categories such as case, number, gender, tense, person, or mood without changing the word class or core meaning of the word. For example, the -us of Latin genus is a nominative singular neuter noun ending, the -a of Latin genera is a nominative plural neuter noun ending, and the -is of Latin generis is a genitive singular neuter ending. Genus means “one genus,” genera means “not one genus,” and generis means “of one genus.” All three are forms of the same word. Classical endings are akin to inflectional suffixes in English. Inflectional affixes create new forms of the same word.

A suffix is a derivational morpheme that attaches to the end of a base to form a new word, often changing the word class or core meaning. For example, the Latin diminutive masculine -ulus suffix attaches to the stem reg- of the noun rēx (genitive rēgis) meaning “king” to form the new word rēgulus meaning “little king, prince.” The Latin diminutive feminine -ula suffix attaches to the stem rēgīn- of the noun rēgīna (genitive rēgīnae) meaning “queen” to form the new word rēgīnula meaning “little queen, princess.” Both rēgulus and rēgīnula are new words distinct from rēx and rēgīna. Classical suffixes are akin to derivational suffixes in English. Derivational suffixes create new words. (All English prefixes are also derivational.)

Unlike the -ex final nouns like vertex in which the -ic- of the oblique stem (vertic-) belongs to the base derived from the oblique stem (<Vertice>), the English -ix suffix borrowed from the Latin -īx suffix is a separate morpheme. Latin noun suffixes decline just like Latin nouns, with different forms for different numbers and cases. For example, the nominative plural of Latin -īx is -īcēs and the genitive singular is -īcis. English often borrows multiple forms of the same suffix from Latin and can borrow derived forms that develop through other languages such as French. For example, English borrowed the -ulus suffix of calculus from the Latin masculine singular -ulus. English also borrowed the masculine plural -uli of calculi, feminine singular -ula of formula, feminine plural -ulae of formulae, neuter singular -ulum of frenulum, neuter plural -ula of frenula, and singular masculine ablative -ulo of modulo from the Latin forms. English additionally developed the -(u)le suffix, which surfaces as -ule in circular and -le as in circle, via French -ule from Latin -ulus and its forms.

English likewise borrowed and developed multiple suffixes from the Latin -īx, which is a feminine suffix. The plural form of Latin -īx is -īcēs, which English borrowed as the plural suffix -ices. The suffix of plural appendices, matrices, helices, animatrices, janitrices, and sculptrices is -ices. (Note that, for helix and helices, the -ix and -ices originated in Ancient Greek as -ix and -ikes but passed through Latin as helix and helicēs and then into English.)

English also developed a related -ic(e) suffix via French -ice as in animatrice (female animator) and matrice (obsolete form of matrix). The -ic(e) suffix accounts for morphological relatives such as appendicalgia, appendiciform, eradicate, helical, matriculand, and varicose. (Note that the English plurals animatrices and matrices are homographic homophones of the Latin plurals animatrices and matrices but that the English plurals end in -ice + -es while the Latin plurals end in -ices.)

(Note that English also has two other -ice suffixes. The -ice in the words avarice, justice, malice, service, and solstice is an abstract noun suffix that comes from Anglo-Norman and Old French -ice, -ise from Latin -itium from -itia from -ia. The -ice in the word Parthenice is an adjective suffix denoting “of, pertaining to” that comes from the Latinized form of Ancient Greek -ikḗ from -ikós.)

Understanding the morphology of singular~plural pairs like matrix~matrices, helix~helices, and animatrix~animatrices requires understanding that the Latin -īx (and Ancient Greek -ix) is a suffix, not an inflectional ending or final graphemes of a root. The -īx/-ix forms feminine nouns. The plural forms are Latin -īcēs and Ancient Greek -ikes. As with other classical suffixes, English borrowed multiple forms of the suffix. In the case of -īx/-ix, English borrowed the singular -ix and plural -ices along with -ice via French through oblique Latin forms -īcem and -īcēs. A plural form such as sculptrices on which the -ices affixes to another suffix is as straightforward as <Sculpt + (o)r + ices → sculptrices> because the -ices is simply another suffix.