То, что and Тот, кто (Free Relatives)

English says "I believe what you said" and "Whoever wants to can leave" with a single bare word doing double duty. Russian splits the job in two: a demonstrative antecedent (то "that" / тот "the one") in the main clause, plus a relative pronoun (что "which" / кто "who") opening the subordinate clause. The result — то, что and тот, кто — is the standard way to express English "what" (= "that which") and "who(ever)" (= "the one who"). The thing that makes this hard for English speakers is that both halves decline, and they decline by different rules: то/тот takes whatever case its role in the main clause requires, while что/кто takes whatever case its role in the subordinate clause requires. Get those two cases from two different clauses and you've mastered the construction.

то, что = "that which / what"

Use то, что when the antecedent is a thing, an idea, or a whole situation — never a person. The literal sense is "that — namely, which…". The comma before что is obligatory in writing: it's two clauses.

The trick is to compute the two cases separately:

• то gets its case from the main clause (subject? object? object of a preposition?).
• что gets its case from the subordinate clause (subject of it? object of it?).

In those three sentences the subordinate что never changed (it's always the object of сказа́л, so accusative — and что happens to look identical in nom. and acc.), but то morphed into то → о том → с тем purely because of its main-clause job. That is the whole skill.

тот, кто = "the one who / whoever"

Use тот, кто when the antecedent is a person. Same machinery: тот declines by its main-clause role, кто by its subordinate-clause role.

Note the last example: тем is plural ("those") because helping several people, while кому́ is dative because of ну́жно inside its own clause. Two clauses, two completely independent case decisions — and even number can differ between them in spirit, though кто itself is grammatically singular and takes singular agreement (тот, кто зна́ет; never *кто зна́ют).

The antecedent is usually obligatory

This is the structural difference from English. English freely drops the antecedent: "What you said is true," "Whoever wants to can leave" — no "that," no "the one." Russian normally keeps то/тот. Dropping it ("Что ты сказа́л — пра́вда" as a relative) is at best marked and usually wrong, because что/кто alone would be read as the *question word ("What did you say?"), not as a relative.

There is one common environment where the antecedent can be omitted: short generic sayings and headlong colloquial speech ("Кто не рабо́тает, тот не ест" actually keeps both, but you'll hear reduced variants). For learner production, always include то/тот — it is never wrong, and omitting it usually is.

то, что vs. the conjunction что

Beware a clash: the word что also serves as the plain conjunction "that" (Я зна́ю, что ты прав — "I know that you're right"). The difference: in то, что the что is a relative pronoun filling a noun slot inside its clause (you can ask "что?" of it); in the conjunction use, что is just glue and fills no slot. The presence of то is your signal — то, что is the free-relative; bare что after a verb of knowing/saying is usually the conjunction.

Common Mistakes

Key Takeaways

• то, что = "that which / what" (things, ideas); тот, кто = "the one who / whoever" (people).
• Two clauses, two cases. The antecedent то/тот is cased by its main-clause role; the relative что/кто by its subordinate-clause role.
• The antecedent is normally obligatory in Russian — unlike English bare "what/who". Always include то/тот.
• After a preposition, the antecedent carries the case: с тем, что…; о том, что…; not the relative.
• тот, кто is singular for agreement: тот, кто зна́ет, мо́жет…
• Distinguish the free-relative что (fills a noun slot, paired with то) from the plain conjunction что ("that," just glue, no то).