Learn Hardcore Russian: Эта форма показывает, что кто‑то был обязан что‑то сделать в прошлом. - This form shows that someone had to do something in the past.

The verb показывает is in the present tense because it refers to what the form does now or in general, not to when the obligation existed.

Эта форма показывает… = This form shows… (a general, timeless statement about meaning)
Inside the что‑то был обязан сделать clause, we switch to the past (был) because that clause describes an obligation that existed in the past.

So you have:

outer verb: present (what the form does as a grammatical form),
inner situation: past (what someone was obliged to do).

This is very similar to English: “This form shows that someone was obliged to do something in the past.”

What does эта форма mean here? Is it a physical form (like a document) or a grammatical form?

By itself, форма can mean:

shape, form (physical shape),
form, application form (a document),
form in the grammatical sense (verb form, case form, etc.).

In grammar explanations, эта форма almost always means “this grammatical form” (for example: this tense, this verb ending, this construction). So here it is not about paperwork but about a specific grammatical form in Russian that carries the meaning “someone was obliged to do something in the past.”

What exactly is был обязан grammatically, and what does it mean compared to just using a past tense verb?

Был обязан is:

был – past tense of быть (“to be”),
обязан – short-form adjective (historically from a participle) meaning “obliged, under an obligation, bound (to)”.

Together кто‑то был обязан (что‑то сделать) literally means:

“someone was obliged (to do something)”
very close to “someone had to (do something)” but with a slightly more formal / strong sense of duty.

It’s not just a normal past tense verb; it’s a copula + predicative adjective construction that expresses obligation, often with a nuance of duty, requirement, responsibility (moral, legal, formal, etc.).

How is был обязан different from должен был or надо было?

All three can refer to obligation in the past, but they differ in tone and nuance:

кто‑то был обязан что‑то сделать
- “someone was obliged / had an obligation to do something”
- formal/strong duty, often moral, legal, or contractual
- sounds more official or serious.
кто‑то должен был что‑то сделать
- “someone was supposed to / had to do something”
- very common, neutral way to express past obligation or expectation.
кому‑то надо было что‑то сделать
- “someone needed to / had to do something”
- more about necessity (practical need, situation) than duty;
- less formal, often more conversational.

In your sentence, because it’s explaining a grammatical form, был обязан fits well: it sounds clear, neutral-to-formal, and strongly connects to the idea of obligation.

Why do we use сделать (perfective) and not делать (imperfective)?

In Russian, the choice of aspect after verbs of obligation is very meaningful:

сделать (perfective) = to do / make (and complete) something once.
делать (imperfective) = to be doing / habitually do something, or to refer to the action without focusing on completion.

With обязан (or должен, надо), you typically choose:

perfective if the obligation is to carry out a whole, completed action:
- был обязан что‑то сделать = “was obliged to (actually) do something (and get it done).”
imperfective if the obligation is about an ongoing process, repeated action, or general activity:
- был обязан что‑то делать = “was obliged to be doing something / to do something regularly.”

Here, the sentence is talking about “having to do something in the past” as a single completed obligation, so сделать is natural.

Could we say кто‑то был обязан сделать что‑то instead of кто‑то был обязан что‑то сделать? Is there any difference?

Both word orders are grammatically correct:

кто‑то был обязан что‑то сделать
кто‑то был обязан сделать что‑то

The difference is very small and mostly about rhythm and focus:

что‑то сделать keeps the indefinite object (что‑то) close to the modal meaning (обязан), forming a kind of block: “obliged to do something.”
сделать что‑то mirrors the more typical verb + object structure: “to do something.”

In most neutral contexts, both sound fine. Many natives might not even notice a difference here. Learners can treat them as interchangeable unless a specific focus or emphasis is being discussed.

Why do кто‑то and что‑то have a hyphen? How is this different from writing them as two words?

In Russian, ‑то is an indefinite postfix that attaches to pronouns:

кто → кто‑то (someone)
что → что‑то (something)
где → где‑то (somewhere)
and so on.

It is always written with a hyphen, never as a separate word.

кто‑то = “someone, some person”
что‑то = “something”

If you write кто то, что то as two separate words, it is either wrong or means something else (like “кто то сказал” → “someone said” in very colloquial, sloppy writing; but in standard writing it should still be кто‑то).

So in your sentence, кто‑то and что‑то must have the hyphen to show they are indefinite pronouns.

Why is it что‑то and not что‑нибудь? What is the difference in meaning?

Both что‑то and что‑нибудь can translate as “something”, but they differ in nuance:

что‑то
- “some thing” that is vaguely specific: the speaker thinks of something definite, but doesn’t (or doesn’t want to) name it.
- more neutral and common in statements.
что‑нибудь
- often means “anything (at all)” or “whatever.”
- more typical in:
  - questions: Хочешь что‑нибудь съесть? – “Do you want anything to eat?”
  - negatives and conditions: Если что‑нибудь случится… – “If anything happens…”

In кто‑то был обязан что‑то сделать, we want a neutral “someone was obliged to do something (unspecified)”, not really “do anything at all,” so что‑то is more natural.

How does обязан change with gender and number? Would the sentence look different if we knew the subject?

Yes, обязан agrees with the subject in gender and number. It’s a short-form adjective, so it changes as follows:

masculine singular: обя́зан
- Он был обя́зан что‑то сделать. – “He was obliged to do something.”
feminine singular: обя́зана
- Она была́ обя́зана что‑то сделать. – “She was obliged to do something.”
neuter singular: обя́зано (rare in this sense)
plural (all genders): обя́заны
- Они́ были обя́заны что‑то сделать. – “They were obliged to do something.”

In your original sentence, кто‑то is indefinite, so we use the default masculine singular form: был обя́зан.

What case is что‑то in, and why does it look the same as the base form что?

In что‑то сделать, что‑то is the direct object of сделать, so it is in the accusative case.

For this pronoun:

что (nominative)
что (accusative)

The forms are identical; the case is determined by the function in the sentence, not by a visible ending.

So even though что‑то looks unchanged, we know it’s accusative because it answers “What to do?” and is the thing being done: сделать (что?) что‑то.

Do we really need в прошлом if был обязан is already past? Isn’t that redundant?

You’re right that был обязан already indicates the past, so grammatically you don’t need в прошлом to show past time.

However, в прошлом:

makes the time reference explicit and very clear, which is helpful in grammar explanations,
can indicate “in the past in general” (as a time frame), not just a single moment,
contrasts with other possible time frames, like:
- …что кто‑то будет обязан что‑то сделать в будущем. – “…that someone will be obliged to do something in the future.”

In a short grammar note, adding в прошлом simply emphasizes that this form is specifically associated with past-time obligation.

How should I pronounce the whole sentence? Where are the main stresses?

Here’s the sentence with stress marks:

Э́та фо́рма пока́зывает, что кто́‑то был обя́зан что́‑то сде́лать в про́шлом.

Key points:

Э́та – stress on э.
фо́рма – stress on фо.
пока́зывает – stress on ка.
кто́‑то, что́‑то – stress on кто, что; ‑то is unstressed.
обя́зан – stress on я.
сде́лать – stress on сде.
про́шлом – stress on про́.

Also note vowel reduction in unstressed о (pronounced more like [a]), for example in форма ([фо́рма] but with reduced final a) and показывает.