Learn Hardcore Vietnamese: Tôi đã gặp mẹ của Lan ở siêu thị hôm qua. - I met Lan’s mother at the supermarket yesterday.

đã is a past‐perfective marker in Vietnamese. It indicates that the action (gặp – “meet”) is completed. In English we naturally translate it as “met” rather than “meet.” Without đã, the sentence would be ambiguous about time:

Tôi gặp mẹ của Lan ở siêu thị hôm qua still means “I met Lan’s mother yesterday at the supermarket,” but adding đã makes the past‐completion aspect explicit.

Why do we say mẹ của Lan instead of just mẹ Lan?

của is the possessive/genitive marker (“of”).

mẹ của Lan literally “mother of Lan.”
In spoken Vietnamese you can drop của and say mẹ Lan, which is shorter and very common. Including của is slightly more formal or clear, especially in writing or when emphasizing the relationship.

Why isn’t there a classifier (like cái or con) before mẹ?

Kinship terms (mẹ, bố, anh, chị…) do not take classifiers before them. They function like proper nouns when referring to someone’s parent or sibling. So you say mẹ Lan or mẹ của Lan without adding con, cái, etc.

Why is ở used before siêu thị? Could we use tại instead, or drop the preposition entirely?

ở marks the location where the action takes place and is very common in everyday speech.

tại is more formal (often in writing or announcements).
You generally need a location marker; dropping it (e.g., “gặp… siêu thị”) sounds unnatural.
So “ở siêu thị” = “at the supermarket.”

Why is the time phrase hôm qua placed at the end of the sentence? Can it go somewhere else?

Time expressions in Vietnamese are flexible. You can place hôm qua:
1) At the beginning: Hôm qua, tôi đã gặp…
2) After the subject: Tôi hôm qua đã gặp…
3) At the end (as in your sentence).
All are correct; the choice depends on emphasis and style. Putting it at the end is very natural in casual speech.

Why do we include Tôi when English sometimes omits “I” in casual “met Lan’s mom yesterday”?

Vietnamese typically marks the subject explicitly, especially in writing or to avoid ambiguity. In clear context, you can drop Tôi and just say Đã gặp mẹ của Lan…, but most learners and speakers prefer to keep Tôi to clarify who performed the action.

What is the basic word order in Tôi đã gặp mẹ của Lan ở siêu thị hôm qua?

The core pattern is:
Subject + (Aspect Marker) + Verb + Object + (Location) + (Time)
i.e.
Tôi + đã + gặp + mẹ của Lan + ở siêu thị + hôm qua
Remember, location and time are movable adverbials and can shift for emphasis.