Learn Hardcore Vietnamese: Tôi đã rất vui khi gặp lại bạn bè cũ ở trường. - I was very happy to meet old friends again at school.

đã is an aspect marker showing that the feeling and meeting happened in the past. Vietnamese doesn’t have verb conjugation for tense, so learners use đã (completed action) or sẽ (future) to place actions in time. Here it turns “I am happy” into “I was happy.”

Why is rất placed before vui, and what is the difference between saying rất vui vs. just vui?

rất is an intensifier meaning “very.” You put it directly in front of an adjective or stative verb.

vui = “happy”
rất vui = “very happy”
Without rất, you still say you were happy, but with less emphasis.

Why is khi gặp lại bạn bè cũ placed after the main clause instead of before it?

In Vietnamese, you can put time clauses (introduced by khi, “when”) either before or after the main clause. Placing khi gặp lại bạn bè cũ after Tôi đã rất vui sounds natural and keeps the focus on your emotion first, then explains why.

What’s the difference between gặp and gặp lại?

gặp simply means “to meet.”
gặp lại literally adds lại (“again”), so it means “meet again” or “re-encounter.” Since you had already met these friends in the past, you need lại to convey reunion.

Why is it bạn bè cũ instead of các bạn cũ or bạn cũ?

bạn bè already implies “friends” (plural), so you don’t need các (the plural marker).
cũ here qualifies the friendship or people, “old” as in “long-time” or “former.”
You could say các bạn cũ but it’s slightly more formal/explicit. bạn cũ is also okay but might lean toward “ex-friend” in some contexts. bạn bè cũ is the most neutral for “old friends.”

Could I use tại trường instead of ở trường?

Yes, both ở trường and tại trường mean “at school.”

ở is the general preposition “at/in/on.”
tại is more formal and often used in writing.
In everyday speech, ở trường is more common.

Why do we not repeat the subject Tôi in the clause khi gặp lại bạn bè cũ?

Vietnamese drops the subject in subordinate clauses when it’s the same as the main clause. Since Tôi is already the subject of the sentence, you omit it in khi gặp lại… to avoid redundancy.

Is vui a verb or an adjective in Vietnamese?

Vietnamese doesn’t sharply distinguish verbs from adjectives like English. vui behaves like an adjective (“happy”), but it can also act like a verb (“to be happy”). In Tôi đã rất vui, it functions as a stative verb describing your state.