Learn Hardcore Vietnamese: Ngày mai, Lan sẽ gọi khách sạn.

Vietnamese is quite flexible with time expressions, but putting Ngày mai at the beginning is very common and natural. It sets the time frame first, like saying Tomorrow, Lan will call the hotel.

You can also say:

Lan sẽ gọi khách sạn ngày mai.
Both mean the same thing. The difference is just focus:
Ngày mai, Lan sẽ gọi khách sạn. – slightly emphasizes tomorrow.
Lan sẽ gọi khách sạn ngày mai. – slightly emphasizes the action, with time added at the end.

The comma after Ngày mai is optional in everyday writing, but often used to mark the pause.

Is sẽ always necessary to talk about the future?

No, sẽ is not strictly necessary. Vietnamese often omits explicit future markers when the context already makes the time clear.

All of these can be used, depending on nuance:

Ngày mai, Lan sẽ gọi khách sạn.
Neutral, clear future: Lan will call…
Ngày mai, Lan gọi khách sạn.
Still future because of Ngày mai; feels a bit more matter-of-fact, like a scheduled plan.

Other future-related words:

định – intend to (intention):
Lan định gọi khách sạn.
sắp – about to, soon (near future):
Lan sắp gọi khách sạn.

So sẽ is a general future marker, but not mandatory.

What exactly does gọi mean here? Is it “to call (by phone)” or something else?

In this sentence, gọi means to call by phone.

gọi is flexible and can mean:

to call by phone:
Lan sẽ gọi khách sạn. – Lan will phone the hotel.
to call / shout to someone:
Tôi gọi anh mà anh không nghe. – I called you but you didn’t hear.
to order (food/drink) in some contexts:
Gọi thêm một ly cà phê. – Order one more coffee.

Here, because the object is khách sạn (hotel), the default interpretation is calling the hotel by phone.

Why is there no word for the or a before khách sạn?

Vietnamese does not have articles like the or a/an. The bare noun khách sạn can mean:

a hotel
the hotel
hotels (in some contexts)

The exact meaning depends on context. If you want to be more specific, you can use:

một khách sạn – a/one hotel (non-specific)
khách sạn đó / khách sạn ấy – that hotel (specific)
khách sạn này – this hotel

In your sentence, Ngày mai, Lan sẽ gọi khách sạn, it’s understood from context whether it’s the hotel you already know about, or a hotel in general.

Should there be a classifier before khách sạn, like một cái khách sạn?

Normally, countable nouns can take a classifier, but for many place-type nouns (like nhà hàng restaurant, khách sạn hotel, trường school), the classifier is often omitted when you’re just talking about them generally.

Typical patterns:

một khách sạn – one hotel (no classifier, this is common and natural)
một cái khách sạn – technically possible but sounds odd; cái is not usually used with khách sạn.
một cái bàn – one table (here cái is natural, because bàn is a typical object).

So:
Ngày mai, Lan sẽ gọi khách sạn. – perfectly natural.
If you want to stress one particular hotel, just use một khách sạn or name it specifically.

Is Lan functioning as the subject here, like in English?

Yes. The basic structure here is very similar to English SVO word order:

Lan – subject (the person doing the action)
sẽ gọi – verb phrase (will call)
khách sạn – object (the thing being called)

So structurally:

English: Lan will call the hotel.
Vietnamese: Lan sẽ gọi khách sạn.

Vietnamese does not mark subjects with case endings or changes; word order does the job.

Can I replace Lan with a pronoun like “she” or “I”? How would that change the sentence?

Yes, you can. Just replace Lan with the appropriate pronoun (or kinship term) depending on who is speaking and who Lan is to them.

For example:

Ngày mai, tôi sẽ gọi khách sạn. – Tomorrow, I will call the hotel.
Ngày mai, cô ấy sẽ gọi khách sạn. – Tomorrow, she will call the hotel.

Colloquial Vietnamese often uses kinship terms instead of neutral pronouns:

Ngày mai, em sẽ gọi khách sạn.
Ngày mai, anh sẽ gọi khách sạn.

Which one you choose depends on relative age, gender, and relationship.

Is the comma after Ngày mai required?

No, it’s not strictly required, but it’s common and recommended in more careful writing.

Ngày mai, Lan sẽ gọi khách sạn.
Ngày mai Lan sẽ gọi khách sạn.

Both are acceptable. The comma simply marks a natural pause after the time phrase. In handwriting and informal text messages, many people omit it.

How do I pronounce ngày and ng at the beginning? It’s different from English.

The ng in ngày is like the ng sound at the end of English sing, but moved to the beginning of the syllable.

ngày ≈ ngai (with a low-rising tone)

Tips:

Start with your tongue in the ng position (as in sing).
Keep the back of your tongue touching the soft palate briefly, then release into the vowel.
Don’t put a g sound like guh before it.

Also note the tone: ngày has the huyền (falling) tone, so your pitch should fall slightly as you say it.

What’s the difference between sẽ gọi khách sạn, gọi cho khách sạn, and gọi đến khách sạn?

All involve calling, but the phrasing is a bit different:

Lan sẽ gọi khách sạn.
Most natural, neutral: Lan will call the hotel (by phone).
Lan sẽ gọi cho khách sạn.
Also acceptable; cho can mark the recipient. Often used when focusing on doing something for someone or sending something to them. With khách sạn, it still just means calling the hotel.
Lan sẽ gọi đến khách sạn. / Lan sẽ gọi tới khách sạn.
Emphasizes the destination more; still understandable but sounds a bit more formal/literal. In everyday speech, people usually just say gọi khách sạn.

In standard everyday conversation, gọi khách sạn is the most common choice.

How would I say “Tomorrow, Lan will call the hotels” (plural)?

You can show plurality with words like những or các, or by context.

Common options:

Ngày mai, Lan sẽ gọi các khách sạn.
Often implies a specific set of hotels (e.g., a known list).
Ngày mai, Lan sẽ gọi những khách sạn đó.
Tomorrow, Lan will call those hotels.
In casual speech, context alone can show it’s plural:
Ngày mai, Lan sẽ gọi khách sạn – if the conversation is clearly about several hotels, this can be understood as plural.

If you want to clearly mark plural, các khách sạn or những khách sạn is safest.

Could I add đi like Lan sẽ đi gọi khách sạn to sound more natural?

In this context, you generally do not add đi.

Lan sẽ gọi khách sạn. – Correct and natural: Lan will call the hotel.
Lan sẽ đi gọi khách sạn. – Sounds like Lan will go (somewhere) to call the hotel, implying movement first.

đi literally means to go, and is sometimes used as a softening particle with requests (e.g., đi đi, ăn đi), but with gọi khách sạn in a simple future statement, adding đi usually suggests physical movement, not just making a phone call.

So for your sentence, stick with Lan sẽ gọi khách sạn.