Learn Hardcore Korean: chinguwa yaksokhaessjiman sigani an majayo. - I made an appointment with a friend, but our times don’t match.

-지만 is a conjunction meaning “but” or “although.” You attach it to the verb stem (in this case 약속했 + 지만) to contrast two clauses. So 친구와 약속했지만 literally means “I made plans with a friend, but…” and sets up the objection in the second clause.

What does 친구와 mean, and why use -와 here?

친구와 means “with a friend.” The particle -와 attaches to nouns ending in a vowel (like 친구) to express “with” (or coordinate “and”). If the noun ended in a consonant, you’d use -과 instead.

What’s the difference between -와/과 and -랑/이랑?

Both pairs mean “with” (or “and” when joining nouns).
• -와/과 is more formal or written.
• -랑/이랑 is more colloquial and common in everyday speech.
So 친구와 (formal) = 친구랑 (casual), both “with a friend.”

What does 약속하다 mean in this context? Could I use 만나다 instead?

While 약속하다 literally means “to promise,” in everyday Korean it often means “to make plans/appointments (to meet).” You could rephrase the sentence as:
“친구와 만나기로 했지만 시간이 안 맞아요.”
(“I decided to meet my friend, but our times don’t work out.”)
Both sentences convey the same idea; 만나다 focuses on the meeting itself, 약속하다 on the act of arranging it.

What does 시간이 안 맞아요 mean, and how does 안 맞다 work?

시간이 맞다 literally means “the time fits” or “the schedule lines up.” By adding 안, you negate it:
시간이 안 맞아요 = “The times don’t match” / “Our schedules don’t line up.”

Why use 안 for negation here instead of 못?

안 is a general negator meaning “not.” 못 implies inability (“cannot”). Here, you’re simply stating that the schedules do not match (a factual negation), not that you cannot match them because you lack ability. Therefore 안 맞아요 is more natural than 못 맞아요.

Can you drop the subject particle 이 in 시간이 안 맞아요 and just say 시간 안 맞아요?

Yes. In casual spoken Korean, it’s common to omit particles when the meaning remains clear. 시간 안 맞아요 is perfectly natural in informal contexts.

What level of politeness/formality is this sentence in?

It ends with -요 (안 맞아요), which is polite informal speech (해요체). It’s appropriate for everyday conversation with acquaintances, coworkers, or strangers you’re not on intimate terms with.