oba / obě

The word for 'both' in Czech behaves as a determiner or pronoun, though in traditional Czech grammar, it is classified as a numeral (číslovka). While it declines similarly to the number two (dva/dvě), remember the semantic difference: dva means the quantity 'two', whereas oba means 'both' (the complete, known set of two). It retains historical dual endings that make its declension unique.

1. Nominative and Accusative (Gender Split)
In the nominative and accusative cases, you must choose between two forms based on the noun's gender:

• Oba: Used for all masculine nouns (animate and inanimate) (e.g., Vidím oba bratry - I see both brothers).
• Obě: Used for feminine and neuter nouns. A common misconception is that obě is only feminine, but it is required for neuter nouns too (e.g., obě auta - both cars).

2. Mixed-Gender Groups
Due to the Czech gender hierarchy, the masculine gender takes precedence. If you are referring to a mixed group containing a masculine animate noun (e.g., a brother and a sister), you must use oba and the corresponding -i verb ending (e.g., Bratr a sestra přišli oba. - The brother and sister both came.). For mixed inanimate groups that cross the oba/obě boundary (i.e., a masculine inanimate noun mixed with a feminine or neuter noun, e.g., a table and a chair), there is no valid form of oba/obě. (Note: If the mixed group consists only of feminine and neuter nouns, such as židle a křeslo, the form obě is perfectly valid.) Instead, for groups with conflicting forms, Czechs use obojí (e.g., Stůl a židle, obojí stálo v rohu. - The table and chair, both stood in the corner.). Note that obojí is grammatically singular and takes a neuter singular verb, which can be counterintuitive for English speakers who expect a plural verb for 'both'. Alternatively, use the correlative conjunction jak... tak... (e.g., Jak stůl, tak židle stály v rohu. - Both the table and the chair stood in the corner.).

3. Oblique Cases (Case Collapse)
In all other cases, the gender distinction disappears entirely. Czech uses fossilized dual endings instead of standard plural ones:

• Genitive & Locative: obou (mirrors dvou; e.g., bez obou bratrů - without both brothers, o obou ženách - about both women)
• Dative & Instrumental: oběma (mirrors dvěma; e.g., k oběma autům - to both cars, s oběma rodiči - with both parents). Important: When used with paired body parts (hands, feet, eyes, ears) in the instrumental case, these nouns also retain historical dual endings, creating a perfect match with oběma (e.g., s oběma rukama - with both hands, před oběma očima - before both eyes). Using standard plural endings here is a common mistake.

Note on Register: In spoken Common Czech, you will frequently hear forms like obouch or obouma, or forms with a prothetic v- (Common Czech prothetic v- contrast) like voba/vobě. However, the Czech Language Institute (ÚJČ) considers obouch and obouma strictly non-standard and incorrect in formal writing. Additionally, beware of the hypercorrect form oběmi; oběma is the only correct instrumental form.

4. Grammatical Behavior
Unlike Genitive plural after five and higher numerals, oba/obě does not force the following noun into the genitive. It simply agrees with the noun's case. When used as a subject, it requires a plural verb, and the past participle must reflect the gender with the endings -i / -y / -a (e.g., oba muži šli - both men went, oba hrady stály - both castles stood, obě ženy šly - both women went, obě auta jela - both cars went) (Past-tense plural gender endings).

5. Advanced Nuances

• Emphasis: Czechs often say oba dva or obě dvě to add emphasis ("both of the two").
• Oboj/Oboje: Do not confuse oba/obě (used for individual, countable items) with obojí (both kinds/mass nouns, e.g., obojí víno - both kinds of wine) or oboje (used with plural-only nouns, pluralia tantum). Crucially, obojí is grammatically singular and requires a neuter singular verb (e.g., Obojí bylo dobré. - Both were good.), unlike English where 'both' takes a plural verb. You must use oboje for pluralia tantum: oboje dveře (both doors) and oboje kalhoty (both pairs of pants).