Learn Hardcore Ukrainian: Цей день сумний, бо подруга поїхала. - This day is sad because my female friend left.

Ukrainian usually drops the present-tense verb бути (to be). So instead of saying Цей день є сумний, people just say Цей день сумний. Using є is possible in formal/contrastive contexts, but in everyday speech the zero-copula is the norm.

What does бо mean, and do I need the comma before it?

бо means “because.” Yes, you put a comma before it when it connects clauses: …, бо …. You can also say тому що or оскільки (a bit more formal/explicit); the comma is still required before them.

Why is it цей день, not ця/це/ці день?

Because день (day) is masculine singular in the nominative, and the demonstrative must agree: цей (masc.), ця (fem.), це (neut.), ці (plural). Hence цей день.

Why сумний and not сумно or сумним?

сумний is an adjective agreeing with день in gender/number/case: день сумний.
сумно is impersonal (“it’s sad”): Сьогодні сумно (no specific subject).
сумним (instrumental) isn’t used here; with the present zero-copula you use nominative: день сумний.

How does поїхала show that the subject is female?

Past-tense verbs agree with gender and number:

masculine: поїхав
feminine: поїхала
neuter: поїхало
plural: поїхали So поїхала tells you the subject is feminine singular.

What’s the difference between поїхала and їхала?

Aspect. поїхала (perfective) is a completed event (“she left/went by transport”). їхала (imperfective) is ongoing or habitual (“she was going/used to go”). As a reason for a present feeling, the completed action поїхала is natural.

When would I use пішла instead of поїхала?

Use пішла for motion on foot and поїхала for motion by vehicle:

Вона пішла додому. (She went home on foot.)
Вона поїхала додому. (She went home by transport.)

Does подруга mean “girlfriend” (romantic)?

Typically подруга means a female friend (non-romantic). For a romantic girlfriend, use дівчина (girlfriend) or кохана (beloved).

Where is the possessive “my”? Why not моя подруга?

Ukrainian often omits possessives when context makes ownership obvious. подруга will often be understood as “my friend.” You can add моя for clarity or emphasis: …бо моя подруга поїхала.

Can the word order change?

Yes, Ukrainian word order is flexible for emphasis. Alternatives include:

Сумний цей день, бо подруга поїхала. (fronts the adjective)
Цей день сумний, бо поїхала подруга. (focus on the action, then subject) All are grammatical; the original is the neutral order.

What’s the difference between цей день сумний and цей сумний день?

цей день сумний is a full sentence asserting a fact (“this day is sad”).
цей сумний день is a noun phrase used inside another sentence: Я запам’ятаю цей сумний день.

Which case is подруга in here, and why?

Nominative singular. It’s the subject of the second clause. As an object it would be accusative: бачу подругу.

How do I add a destination to поїхала?

Use place prepositions:

до + Genitive (to/towards): …бо подруга поїхала до Києва / до батьків.
в/у + Accusative (into): …бо подруга поїхала в Київ.

Can I say Цей день є сумний?

You generally don’t need є in such present-tense sentences. While it can appear in formal or contrastive contexts, most speakers would simply say Цей день сумний.