3.4.1. The Genders distinguished in Europaio are three: Masculine, Feminine (both are referred to as Animate) and Neuter or Inanimate.
3.4.2. The gender of Europaio nouns is either natural or grammatical.
a. Natural Gender is distinction as to the sex of the object denoted: pater (m.), father ; cena (f.), woman ; wlqos (m.), wolf ; swesor (f.), sister.
NOTE 1. Many nouns have both a masculine and a feminine form to distinguish sex: as, ekwos, ekwa, horse;
NOTE 2. Names of classes or collections of persons may be of any gender: as, armata (f.), army;
b. Grammatical Gender is a formal distinction as to sex where no actual sex exists in the object. It is shown in the form of the adjective joined with the noun: as magnos wlqos (m.), a great wolf; ma dnghu (f.), my language (tongue). The gender of the adjective is thus simply a gender of concordance: it indicates to which noun of a concrete gender the adjective refers to.
3.4.3. The neuter or inanimate gender differs from the other two in inflection, not in the theme vowel. The gender of the animates, on the contrary, is usually marked by the theme vowel, and sometimes by the declension, vocalism and accents.
3.4.4. The neuter does not refer to the lack of sex, but to the lack of liveliness or life. Sometimes, however, animates can be sometimes designated as inanimates.
While the distinction between masculine and feminine is usually straightforward, sometimes the attribution of sex is arbitrary: thus, naus, ship, nave, is feminine, while pods, foot, is masculine.
NOTE. The masculine functions as the negative term in the opposition. This is a purely grammatical utility, one that is only relevant for concordance, and which has to do with the evolution of the IE and its inflection system.
3.4.5. The animate nouns can have:
a. An oppositive gender, marked:
I. by the lexicon, as in pater-mater, bhrater-swesor;
II. by the theme vowel, as in ekwos-ekwa, wlqos-wlqia;
III. by both at the same time, as in wiros-cna [G'na:].
b. An autonomous gender, that does not oppose itself to others, as in the aforementioned naus and pods.
c. A common gender, in nouns that are masculine or feminine depending on the context.
d. An epicene gender, which, although being masculine or feminine, designates both sexes: as the feminine sus (cf. swine), pig.
3.4.6. The gender of a noun can thus be marked by the theme vowel (or sometimes by the inflection), or has to be learnt: it is a feature of a word like any other. In its context, concordance is a new gender mark: a masculine noun has a masculine adjective, and a feminine noun a feminine adjective. However, not all adjectives differentiate between masculine and feminine, a lot of them (those in -i-s, -u-s, -es, -on, and many thematic in -os) are masculine-feminine: only the context, i.e. the noun with which they agree, helps to disambiguate them. This happens also in nouns of the c-type.
3.4.7. So, most of the endings do not indicate gender, as in pater and mater. Only by knowing the roots in many cases, or by the context in others is it possible to determine it. Some of the suffixes determine, though, totally or partially if they are masculine or feminine. These are the following:
1. -os marks masculine when it is opposed to a feminine in -a or -ia, as in ekwos, wlqos. This happens also in adjectives in the same situation, as in newos-newa. In isolated nouns, -os is generally masculine, but some traces of the old indistinctness of gender still remains in this third stage of the language; as in the names of trees (among others). In adjective endings -os which are not opposed to feminine, only concordance decides.
2. -a marks the feminine in oppositions of nouns and adjectives. It is usually also feminine in isolated nouns, in the third declension. But there are also traces of masculines in -a, as, lat. auriga, charioteer, driver; or nauta, sailor, and osl. sluga, server.
3. -ia, is systematically feminine. It is used in nouns, and often in adjectives.
4. Finally, the theme vowels -i and -u are feminines.