Investigating the Latin Third Declension and Oblique Stems: Bases, Stems, and Roots

In my recent word studies, I have been attempting to understand third declension nominal forms in Latin and their relation to English spelling. The Latin third declension refers to the large and diverse group of nouns and adjectives identified by the genitive singular -is ending. This declension group includes masculine, feminine, and neuter genders. Relevant to my current study is that many third declension nouns have a different oblique stem than the nominative singular.

My need to understand the Latin third declension arose as I refined my analysis of the -es Latin and Ancient Greek noun and adjective plural suffix. After days of restudy, I think I finally understand the Latin plural -es and third declension oblique stems.

To begin, English -es as in crises is a plural suffix from the Latin -ēs nominative plural ending. English uses this plural suffix in pairs like crisis~crises, analysis~analyses, axis~axes, basis~bases, and unguis~ungues. Notice the singular nominative -is ending on crisis, analysis, axis, basis, and unguis.

The -es is also the plural ending of third declension nominal forms with singular -is forms and -id- oblique stems. For example, the Latin plural form of proboscis is proboscides. (The Anglicized plural proboscises also exists.) Latin proboscis is a third declension noun. The form proboscis is the nominative singular. The oblique stem is proboscid-, meaning the other noun endings attach to proboscid- rather than probosc-: nominative plural proboscidēs, genitive singular proboscidis, etc. The -ēs and -is are the nominative plural and genitive singular endings that attach to the oblique stem.

Thus, in English, the singular proboscis and plural proboscides have different bases: <Bosc> and <Boscide>. The <Bosc> comes from the Latin singular nominative -boscis, and the <Boscide> comes from the Latin oblique stem -boscid-. Another example is rachis~rachides, which have <Rach> and <Rachide> bases. The -is and -es are noun endings.

Some third declension Latin nouns end in -ūs in the nominative singular and have -ud- oblique stems like palus and paludes, meaning “swamp, marsh.” The base from the Latin nominative singular palūs is <Pale>, and the base from the oblique stem is <Palude>. The -us and -es are noun endings.

Another common example of two bases from a third declension nominative singular and an oblique stem is <Ceps> and <Cipite>. The bound base <Ceps> comes from the nominative singular Latin -ceps, and the bound base <Cipite> comes from the oblique stem -cipite- from forms like the plural -cipites and genitive singular -cipitis. Bases from Latin third declension nominal forms are common in English.

Then there are the Latin nouns that end in -ex in the nominative singular that have -ic- oblique stems. The -ex forms were as easy for me to ascertain as the -id- and -ud- oblique stems. For example, vertex and index are singular nouns with Latin plurals vertices and indices. The bases of the singular forms are <Vert> and <D> from the Latin nominative singular vertex and index. The bases of the plural forms are <Vertice> and <Dice> from the oblique stems vertice- and -dice-. The -ex and -es are noun endings.

<Vert + ex → vertex>
<Vertice + es → vertices>
<In + D + ex → index>
<In + Dice + es -> indices>

I finally concluded that the difference between words like vertex and words like vertices lies in the Latin, specifically Latin stems. My understanding is that a stem is the core of a word to which inflectional affixes attach. For Latin vertex and vertices, the stem of the nominative singular is vert- and the oblique stem is vertic-. The word endings like nominative singular -ex and nominative plural -ēs attach to the stem: vert- + -ex → vertex and vertic- + -es → verticēs.

With the third declension oblique stems, the oblique stems are the older forms, preserving the historical origin, while the nominative singular underwent various changes. The -in-, -ic-, -ud-, and -id- is part of the stem, not a separate morpheme. Thus, the third declension nominal forms often give English two separate but related bases: one from the nominal singular stem and one from the oblique stem. A stem is not further morphologically analyzable. The -ic- in the Latin vertic- stem is part of the stem, not a separate morpheme. Many Latin third declension words simply have a nominative singular stem that differs from the oblique stem. Because of the Latin origin, the bases of English vertex and vertices are related but different.

Although not morphologically segmentable (i.e. a stem is a singular unit), stems are etymologically transparent to determine the root. Importantly, diachronically analyzing the morphemes within a stem reveals the root. A root is the ultimate source of a stem. The Latin singular~plural vertex~verticēs ultimately comes from the Latin vertere. The root of both vert- and vertic- is thus vertere. Similarly, Latin singular~plural proboscis~proboscides ultimately come from the Ancient Greek bóskein. The root of both bosc- and boscid- is thus bóskein. Related morphemes come from the same etymological root.

I have also recently considered whether suffixes with oblique forms can also provide two forms in English. If stems can have oblique forms and those oblique stems can give English bases, what about suffixes with oblique forms? Specifically, I was investigating English words that -tudin- such as altitudinal and fortitudinous. The root of altitudinal is Latin alere via altus. The English altitudinal comes more directly from Latin altitūdō, which comes from altus +‎ -tūdō. Like many third declension nominal forms, the suffix -tūdō also has oblique forms like nominative plural -tūdinēs, genitive singular -tūdinis, and accusative singular -tūdinem. English specifically forms altitudinal from the Latin oblique stem altitūdin-. But that oblique form is not of a nominal form but of a suffix. Because the Latin -tūdō developed into the English -tude, could the oblique -tūdin- have developed into the English -tudine?

The Italian suffix –itudine supports my English -tudine suffix hypothesis. Italian -itudine (more accurately -i- + -tudine) comes from Latin -tūdinem, which is the accusative singular of -tūdō. English developed the word attitudinal through the Italian attitudine. Additionally, the English word plenitudine contains the -tudine suffix without additional suffixes: <Plene + i + tudine → plenitudine>. English has also borrowed multiple forms of the same suffix from Latin suffixes. Consider all the forms of Latin -culus including -culus, -c(u)le, -cula, -culum, and more. I am thus confident in my analysis of both -tude and -tudine suffixes from the Latin -tūdō. The -tude form comes from the nominative singular -tūdō while -tudine comes from the oblique forms.

So, after hours and days of research and contemplation, I have an elegant analysis of English morphemes that come from Latin forms with oblique stems different from the nominative singular. A root is the etymological source of a stem. A stem is the core of a word to which inflectional affixes attach. Latin stems often become English bases. In the case of the Latin third declension, Latin often gives English two different but related bases, one from the nominative singular form and another from the oblique stem. English can also have multiple suffixes from the same Latin suffix including forms from the oblique forms.