kto / co

Polish uses grammatical cases to show the relationship between words. The pronouns kto (who) and co (what) change their forms depending on their role in the sentence.

The Declension Table:

• Nominative: kto / co (Subject)
• Genitive: kogo / czego (Possession, negation (e.g., Affirmative: Co masz? → Negative: Czego nie masz? (What do you have? → What don't you have?)), after prepositions like 'do', or with verbs that inherently require the Genitive case, such as szukać (to look for), słuchać (to listen to), and potrzebować (to need))
• Dative: komu / czemu (Indirect object: Komu pomagasz? (Who are you helping?); with przyglądać się, Czemu się przyglądasz? (What are you looking at?))
• Accusative: kogo (people) / co (things) (Direct object)
• Instrumental: kim / czym (Used for accompaniment with 'z', identifying roles or professions like Kim jesteś?, and 'czym' is used alone for means/instrument)
• Locative: kim / czym (Used after prepositions like 'o', 'w', 'na', 'przy', or 'po' for specific uses, for example for topics or locations. Note that some of these prepositions can also take the Accusative case depending on the context.)

Note: These pronouns do not have a functional Vocative form.

Key Rules:
1. Always Singular: Kto and co have no plural forms. Even if you expect the answer to be multiple people, you must use the singular: Kto tam jest? (Who is there?).
2. Prepositions First: Unlike English, you cannot end a sentence with a preposition. It must come before the pronoun: Z kim? (With whom?) not Kim z?
3. Gender Agreement: Kto always takes masculine singular verbs (e.g., Kto był?), even if you expect the answer to be a woman. Co takes neuter singular verbs (e.g., Co się stało?).
4. Czemu vs. Dlaczego: While czemu is technically the dative of co, it is very commonly used in casual speech to mean 'why'. In formal contexts, dlaczego is preferred. Notice that dlaczego literally consists of 'dla' (for) + 'czego' (Genitive of co), which helps you remember that the preposition dla requires the Genitive case. However, be aware that czemu also literally means 'to what' and can create ambiguity with verbs that govern the Dative case, like przyglądać się (e.g., Czemu się przyglądasz? primarily means 'What are you looking at?').
5. Identical Forms: Notice that for kto, the Genitive and Accusative forms are identical (kogo). For co, the Nominative and Accusative forms are identical (co).
6. Derivative Pronouns: The pronouns ktoś (someone), coś (something), and the negative pronouns nikt (no one) and nic (nothing) largely follow kto and co. Many forms can be recognized by adding the suffix -ś or the prefix ni- to the declined forms (e.g., Genitive: kogoś, czegoś, nikogo, niczego).

The accusative forms reflect the same pattern as masculine animacy: personal kto uses genitive-shaped kogo, while non-personal co keeps nominative-shaped co. The case still depends on syntax: Kogo widzisz? has accusative; Kogo szukasz? has genitive.

These words also link relative clauses: Ten, kto pyta, dowie się więcej (The person who asks will learn more), To, co widzisz, jest moje (What you see is mine). Their case comes from their role inside the relative clause: To, o czym mówisz, jest ważne (What you are talking about is important).

The negative pronoun nic is not a completely mechanical ni- version: Nic nie widzę uses nic in a negated-object construction, and forms such as niczego also occur. Learn the negative-pronoun paradigm separately.