Learn Hardcore Russian: Вчера я должен был работать дома, но друзья позвали меня в парк. - Yesterday I had to work at home, but friends invited me to the park.

So я должен был работать = “I was obliged / I had an obligation to work” (but maybe I didn’t actually do it, which fits well with но друзья позвали…).

Why is it должен был and not conjugated like a normal verb (e.g. я долженал or something)?

Должен is not a normal verb; it’s a short-form adjective that behaves like a predicative word (“obliged”). In Russian you say literally:

я должен – “I am obliged” (present)
я был должен or я должен был – “I was obliged” (past)

There is no verb form like долженал. Instead, Russian uses:

The short adjective должен / должна / должно / должны
Plus the verb быть in the right tense (if needed)
Plus an infinitive: работать, идти, сделать, etc.

So the structure is: я + (был) + должен + инфинитив.

Why is it должен был (masculine) and not должна была? Could it be different?

The form должен был is masculine singular. Russian agreement here depends on the speaker’s gender:

A male speaker: Я должен был работать.
A female speaker: Я должна была работать.

So if the sentence is spoken by a woman, it should be Вчера я должна была работать дома, но друзья позвали меня в парк.

Why is работать in the infinitive? Could it be a different form like работал?

After должен был, Russian requires the infinitive:

должен был + infinitive:
я должен был работать – “I had to work”

If you say:

я работал дома – “I worked at home”

that describes what actually happened, not an obligation.

So:

я должен был работать дома – there was an obligation/plan to work at home (but maybe something prevented it).
я работал дома – I really did work at home.

What is the nuance of я должен был работать дома, но… in terms of actually working? Does it imply I didn’t work?

Often, yes, this pattern suggests that the obligation was not fulfilled or was at least interrupted:

Я должен был работать дома, но друзья позвали меня в парк.

This sounds like:

“I was supposed to work at home, but instead my friends called me to the park (and I probably went).”

The contrast with но (“but”) plus a tempting alternative strongly implies the plan/obligation was broken or not fully carried out.

Why is it дома and not в доме?

Both are grammatically correct, but they mean slightly different things:

дома – an adverb meaning “at home / at my place”.
- работать дома – “to work at home (as opposed to in the office, etc.)”
в доме – “in the house” (inside a particular building).
- работать в доме – “to work in the house (inside that building)” – sounds more physical/location-specific and less like the “home vs office” contrast.

In everyday speech, when you mean “working from home” as opposed to elsewhere, дома is the natural choice:
работать дома – to work at home.

Why is it друзья позвали меня, not друзья позвали мне?

This is about case usage:

позвать кого? – “to call/invite whom?” → needs accusative case.
я → меня (accusative)

So:

друзья позвали меня – “friends called/invited me.”

Мне is dative (“to me”) and is used for verbs that take an indirect object:

дать мне книгу – “to give me a book”
сказать мне – “to say to me”

But позвать uses a direct object, so меня is required.

What’s the difference between позвали and something like пригласили? Could I say пригласили instead?

Both are possible, but the nuance differs:

позвали (from позвать) – “called (over), called out to, asked to come, invited in a casual way.”
Often used for spontaneous or informal invitations:
Друзья позвали меня в парк. – “My friends called me to the park / invited me to come to the park.”
пригласили (from пригласить) – “invited (more formally / deliberately).”
Sounds slightly more official or planned:
Друзья пригласили меня в парк. – “My friends invited me to the park” (could be fine, just a bit more neutral/formal).

In this context, позвали feels more colloquial and spontaneous.

Why is it в парк and not в парке?

The preposition в with different cases expresses different meanings:

в + accusative (в парк) – motion into a place: “to the park.”
в + prepositional (в парке) – location in a place: “in the park / at the park.”

Since позвали implies “called (me) to go somewhere,” we need motion → в парк (accusative).

Examples:

Я иду в парк. – I’m going to the park. (motion)
Я сижу в парке. – I’m sitting in the park. (location)

Why is there a comma before но?

In Russian, но (“but”) normally introduces a separate clause that contrasts with what came before. You place a comma before it:

…работать дома, но друзья позвали меня в парк.

You have two clauses:

я должен был работать дома
(но) друзья позвали меня в парк

They are joined by the coordinating conjunction но, so a comma is obligatory.

Can the word order change, like Я вчера должен был работать дома? Is that still correct?

Yes, several word orders are possible and grammatical. For example:

Вчера я должен был работать дома… (neutral; emphasis slightly on “yesterday” as the time frame)
Я вчера должен был работать дома… (also normal; puts “I” first, very natural)
Я должен был вчера работать дома… (can put light emphasis on “yesterday” as the time of the obligation)

Russian word order is flexible. All of these sound natural in everyday speech, with only subtle differences in emphasis. The most typical, neutral options are Вчера я должен был… or Я вчера должен был….

Could I use поработать instead of работать? What would change?

Yes, but the meaning shifts slightly.

работать (imperfective) – focuses on the process: “to be working / to work (in general).”
поработать (perfective) – suggests working for some time / to get some work done (a bounded, result-oriented action).

Compare:

Я должен был работать дома. – I had to work at home (focus on the ongoing fact of working).
Я должен был поработать дома. – I had to get some work done at home / do some work at home (implies a completed chunk of work).

Both are correct; работать is more neutral here.

What’s the difference between я должен был работать and мне нужно было работать?

Both can translate as “I had to work,” but there is a nuance:

Я должен был работать…
– Stronger sense of duty/obligation, often from rules, people, promises, a schedule.
– Feels more like “I was supposed to / I was obliged to work.”
Мне нужно было работать…
– More about necessity/convenience, less about duty.
– “I needed to work / It was necessary for me to work” (for my own reasons, goals, situation).

In many contexts they overlap, but должен был leans toward obligation, нужно было toward practical necessity.