Ūnus, duo, trēs… Cardinal numbers in Latin are fairly simple after the number 3, since they are all indeclinable: if we want to say four cats, five dogs, or seventeen giraffes, the numbers will not change regardless of the gender or case of the noun it is attached to. This is not the case for numbers one, two, and three. You have already seen the declension of ūnus, -a, -um, an “ūnus nauta” adjective with a distinctive genitive singular in ūnīus and dative singular in ūnī. The numbers for two and three must also be learned, as they have unusual forms. The number two, duo, duae, duo, has masculine, feminine, and neuter forms:        Masculine        Feminine        Neuter Nominative duo duae duo Genitive duōrum duārum duōrum Dative duōbus duābus duōbus Accusative duōs duās duo Ablative duōbus duābus duōbus The forms of duo, duae, duo look like a combination of 1st/2nd declension forms (like magnus, -a, -um) and 3rd declension forms. In fact, the number exhibits forms belonging to the archaic “dual” form, which is a number between singular and plural that is seen only very rarely in Latin. Unusual forms here are colored purple. The number three is trēs, tria, and has one form for the masculine and feminine genders, and a second for neuter:        Masc./Fem.        Neuter Nominative trēs tria Genitive trium trium Dative tribus tribus Accusative trēs tria Ablative tribus tribus You might notice that the forms of trēs, tria are identical to the forms of the masculine, feminine, and neuter i-stems you saw in the previous module: the masculine and feminine forms exhibit i-stem endings in the genitive plural, and the neuter forms exhibit i-stems in the nominative, accusative, and genitive plural. This number is an example of a third declension adjective, which we’ll explore further in the next module!

Vōs igitur ā mē, Iove, ad Thessaliam vocāminī. Select all the correct statements about the main verb in this sentence:

Legite genera dōnōrum quae laudābuntur ab omnibus quī ea vidēbunt. This is a surprisingly tricky sentence to parse out! First, there are three clauses: one main clause (legite genera dōnōrum) and two relative clauses (quae laudābuntur ab omnibus; quī ea vidēbunt). The antecedent of quae is either genera or dōnōrum, since both are neuter plurals. The verb in this clause is passive, and its agent is omnibus (“by all”). Then, this provides the antecedent for the next relative pronoun quī — and, on top of that, ea in the final relative clause refers back to genera dōnōrum! You might structure the sentence like this: Legite genera dōnōrum quae laudābuntur ab omnibus quī ea vidēbunt.

Ablative of time when or within which Numbers can also be useful for designating periods of time: “within three months, Rome will fall”, “in those five years, the farms flourished”, and so on. These specific uses require an “ablative of time when or within which”, which is described further in the following video:

True or false: duo, duae, duo declines like magnus, -a, -um in the plural.

Match the following systems of numerical reckoning with the correct number forms:

What kind of third declension noun do the endings of trēs, tria most resemble?

A bedroom has a volume of 101 m3. What is its volume in cubic kilometers (km3)?

Determine the formal charge on the N in NO2.

Assuming all bonded groups are identical, which of the following VSEPR geometries can produce a nonpolar molecule?