Verbs without Conjugation: Aspect, Completion, and Change

The full event frame gives us the sentence’s outer architecture: time sets the clock, place sets the scene, and the verb names the action. Now we need to make one especially important distinction inside that frame—one that English often hides because English verb forms do several jobs at once.

Chinese separates when an event happens from how the event unfolds.

The first question is about time:

Did it happen yesterday, is it happening now, or will it happen tomorrow?

The second question is about aspect:

Do we see it as completed, ongoing, experienced, or expected?

These questions are related, but they are not the same. Chinese usually answers the first question with context or time expressions. It answers the second with particles, adverbs, or the surrounding structure of the sentence.

Time is usually outside the verb

In English, the verb often carries a visible time signal:

• I eat.
• I ate.
• I will eat.

Chinese verbs generally do not change form in this way. 吃 chī remains 吃 whether you mean “eat,” “ate,” or “will eat.” The time comes from elsewhere:

• 我昨天吃面。Wǒ zuótiān chī miàn. — I ate noodles yesterday.
• 我现在吃面。Wǒ xiànzài chī miàn. — I am eating noodles now.
• 我明天吃面。Wǒ míngtiān chī miàn. — I will eat noodles tomorrow.

The verb itself has not moved through past, present, or future. The time expressions—昨天, 现在, 明天—establish the timeline.

Of course, Chinese can leave the time expression unspoken when the context already supplies it. If someone asks, “你吃饭了吗？”—“Have you eaten?”—the conversation may make the relevant time obvious. Chinese does not need to repeat “today,” “already,” or “yet” if both speakers know what period they are discussing.

This is why translating every Chinese verb into an English tense can be misleading. When you see 吃, do not immediately decide that it means “eat,” “ate,” or “will eat.” First look around it. What time has already been established? What does the conversation make obvious?

Aspect looks inside the event

Time places an event on a calendar. Aspect gives you a camera angle on the event itself.

Imagine a trip to a restaurant. You can locate the trip in time: yesterday, today, or tomorrow. But you can also describe its stage or status:

• The meal was completed.
• The meal is in progress.
• You have had the experience of eating there.
• You are expected to eat there later.

These descriptions do not merely answer when. They answer what kind of view the speaker is taking of the event.

Compare these sentences:

• 我昨天吃饭。Wǒ zuótiān chīfàn. — Yesterday, I ate / had a meal.
• 我昨天吃了饭。Wǒ zuótiān chī le fàn. — Yesterday, I finished eating / did have a meal.
• 我昨天在吃饭。Wǒ zuótiān zài chīfàn. — Yesterday, I was eating.
• 我吃过那家饭店。Wǒ chīguo nà jiā fàndiàn. — I have eaten at that restaurant before.

The first sentence gives a time and an event, but leaves the event’s internal status relatively open. The second presents the meal as completed. The third places the listener inside an ongoing activity. The fourth says that the event belongs to the speaker’s past experience, without focusing on one particular occasion.

Notice that all four may refer to the past. The difference is not simply “past versus non-past.” It is the speaker’s choice of aspect.

Completed is not the same as past

This distinction becomes clearer with 了, which you will meet in detail in the next section. For now, treat it as a signal that the event has reached completion or that a new situation has come about.

• 我买书。Wǒ mǎi shū. — I buy books / I’m buying a book, depending on context.
• 我买了书。Wǒ mǎi le shū. — I bought a book; the purchase is complete.

Adding yesterday can place either sentence in the past:

• 我昨天买书。
• 我昨天买了书。

The word 昨天 tells us when. The 了 in the second sentence tells us how the purchase is viewed: as a completed event. A completed event can occur in the past, but “completed” is not itself the same thing as “past.”

The difference also appears with future events:

• 明天我买书。— Tomorrow I will buy a book.
• 明天我买了书就回家。— Tomorrow, once I have bought the book, I will go home.

The purchase in the second sentence is future, yet 了 can appear because the speaker views it as completed relative to the later action of going home. Aspect is about the event’s position in a larger situation, not simply its position on the calendar.

Four useful views of an event

For a beginner, it helps to keep four broad perspectives separate.

A completed event is presented as having reached its endpoint. Chinese often uses 了 for this, though the exact meaning depends on the sentence.

• 他到了。Tā dào le. — He has arrived / He arrived.

An ongoing event is presented from within its activity. Chinese commonly uses 在, 正在, or 呢 with the verb.

• 他正在开会。Tā zhèngzài kāihuì. — He is in a meeting right now.

An experienced event is presented as something that has happened at least once in the speaker’s experience. Chinese uses 过.

• 我去过北京。Wǒ qùguo Běijīng. — I have been to Beijing before.

This does not normally mean that the speaker is in Beijing now, or even that one specific trip is being discussed. It places “going to Beijing” in the speaker’s experience bank.

An expected event is presented as possible, intended, scheduled, or likely to happen. Chinese uses time expressions and words such as 要, 会, or 将, depending on the context and level of formality.

• 我明天要去北京。Wǒ míngtiān yào qù Běijīng. — I’m going to Beijing tomorrow / I need to go to Beijing tomorrow.
• 他会来的。Tā huì lái de. — He will come / He is likely to come.

The verb 去 or 来 does not change to show the future. The expectation comes from 明天, 要, 会, and the situation around them.

These categories are practical viewing tools, not four rigid boxes. A single sentence can combine them. For example, 明天我已经订好票了 means “Tomorrow, I already have the tickets booked,” where the booking is completed now, while the trip remains future. Chinese lets different events in the same sentence carry different aspectual perspectives.

A reliable reading habit

When you meet a Chinese verb, resist the reflex to ask only, “What tense is this?” Ask two questions instead:

1. What time frame does the context establish?
2. How does the speaker present the event—completed, ongoing, experienced, or expected?

Then inspect the small words around the verb. Time expressions such as 昨天, 现在, and 明天 locate the event. Words and particles such as 在, 过, and 了 shape your view of it. Sometimes there is no overt marker because the context makes the intended reading clear.

This two-question habit prevents one of the most common Mandarin mistakes: treating every sentence as if it were an English sentence with a missing tense ending. Chinese has not omitted the tense. It is organizing the information differently.

Time tells you when the event belongs. Aspect tells you how the speaker wants you to see it.

Once that distinction becomes automatic, the Chinese timeline stops looking like a blank space around an unchanging verb. It becomes a flexible system: context locates the event, and aspect brings its completion, duration, experience, or expectation into focus.

That flexible timeline becomes especially visible with 了. Beginners are often told that 了 means “past tense,” but this shortcut creates more confusion than it solves. 了 does not simply point backward in time. Depending on its position and the meaning of the sentence, it can show either that an event is viewed as complete or that a new situation now exists.

These are related ideas, but they are not the same idea:

Verb-related 了 looks at an event and marks it as completed. Sentence-final 了 tells us that the situation has changed.

The first usually appears directly after the verb or its object. The second appears at the end of the sentence. Sometimes a sentence contains both.

了 after the verb: viewing an event as complete

When 了 follows a verb, it presents the action as a completed whole. It answers a question such as:

Did the event happen all the way through?

Consider the difference between these sentences:

• 我看电影。— I watch movies / I am watching a movie.
• 我看了电影。— I watched a movie; I have watched the movie.

The first sentence merely presents the activity. The second presents the watching as a completed event. The sentence does not itself tell you when it happened. You can add a time expression:

• 我昨天看了电影。— I watched a movie yesterday.
• 我已经看了电影。— I have already watched the movie.
• 我刚才看了电影。— I watched a movie just now.

In each case, the time expression locates the event, while 了 shows how the speaker views it: as finished.

This is why 了 can occur with future time expressions:

• 明天我吃了饭就去上班。— Tomorrow, once I have eaten, I will go to work.

Here 吃了 does not mean “ate in the past.” The eating will happen tomorrow. 了 marks the eating as complete before the next action begins. The useful translation is not always an English past tense; it is often “after doing” or “once [the action] is done.”

A completed event can also be negative, but the form changes. To say that something did not happen, Mandarin normally uses 没有 or 没 before the verb, and does not keep verb-related 了:

• 我看了电影。— I watched the movie.

• 我没看电影。— I did not watch the movie.

• 他买了票。— He bought a ticket.

• 他没买票。— He did not buy a ticket.

This makes sense if you think of 了 as presenting an event as completed. 没 tells us that the event never reached completion, so the completed-event marker is normally absent.

Sentence-final 了: the situation has changed

Now compare a different use:

• 下雨了。— It is raining now / It has started to rain.
• 他病了。— He is ill now / He has become ill.
• 我饿了。— I am hungry now.

In these sentences, final 了 does not primarily mean that someone “rained,” “became ill,” or “completed hunger.” It signals a change from an earlier situation to the current one. The world—or the speaker’s relevant situation—is now different.

Before the change, it was not raining; now it is. Before, he was not ill; now he is. Before, I was not hungry; now I am. The sentence-final position helps you notice that 了 is operating on the whole proposition rather than attaching specifically to an action.

This use appears naturally with adjectives and stative expressions, which do not describe an event that can simply be completed:

• 天黑了。— It has become dark.
• 春天到了。— Spring has arrived.
• 贵了。— It has become more expensive.
• 我明白了。— I understand now; I have come to understand.

The last example is particularly useful. 明白 is not an action like “buy” or “eat.” 我明白了 means that the speaker’s state of understanding has changed. A moment ago, the explanation was unclear; now the speaker understands.

One question: Is the action complete?

When 了 follows a verb, ask:

Is the speaker presenting this particular event as finished?

• 我吃了饭。— I ate / I have eaten a meal.
• 她写了三封信。— She wrote three letters.
• 我们看了那个房子。— We looked at that house.

The focus is on an event reaching its endpoint. The object may help define that endpoint. Compare:

• 他看书。— He reads books / He is reading.
• 他看了这本书。— He read this book / He has read this book.

With a clearly bounded object such as 这本书, the completed reading is easy to understand. But 了 does not guarantee that the action produced a lasting result. 我吃了饭 means that I completed eating a meal; it does not necessarily mean that I am still full.

Another question: Is the situation different now?

When 了 comes at the end, ask:

Is the speaker announcing a new current state?

• 他来了。— He has arrived; he is here now.
• 我不喝咖啡了。— I do not drink coffee anymore / I am no longer going to drink coffee.
• 天冷了。— It has become cold.
• 孩子大了。— The child has grown up.

The last two sentences do not describe a neatly completed action. They point to a changed condition. The final 了 tells the listener: compare the present with what was true before.

This is why final 了 is common when someone notices, reports, or announces a change:

• 快下班了。— It is almost time to finish work.
• 要下雨了。— It is going to rain now / Rain is about to start.
• 我们迟到了。— We are late now.

In 我们迟到了, the sentence can also be understood as “we arrived late,” with 了 attached to the verb phrase. Context determines which perspective is most important: completion of arriving, or the newly true state of being late. Mandarin does not always force the speaker to choose one interpretation completely. The position of 了 provides a strong clue, while context completes the meaning.

The two uses together

A sentence can contain both kinds of 了:

• 我吃了饭了。— I have eaten now.
• 他买了新车了。— He has bought a new car now.

The first 了 follows the verb and marks the eating as completed. The final 了 presents the current situation as changed: the speaker has now eaten, or the relevant meal is now taken care of. In ordinary speech, this combination can sound emphatic, especially when correcting an assumption or announcing that something is settled.

Compare the following three sentences:

• 我吃饭。— I eat / I am going to eat, depending on context.
• 我吃了饭。— I ate; I have eaten.
• 我吃饭了。— I am eating now / I have started eating; the situation has changed.

The final sentence does not necessarily focus on the meal as a completed event. Someone might say it when leaving the room: “I’m going to eat now.” Or, depending on context, it may mean “I’ve eaten now.” The key idea is a transition into the state of eating or having dealt with the meal.

A practical diagnostic

When you meet 了, pause before translating it. Run through these questions:

1. Where is it? Immediately after a verb, or at the end of the sentence?
2. What kind of expression comes before it? An action such as 买, 看, or 写 often supports the completed-event reading. An adjective or state such as 饿, 冷, or 明白 often supports the change-of-situation reading.
3. What question is the sentence answering? “Did it happen?” suggests verb-related 了. “What is different now?” suggests final 了.
4. What does the context require? A sentence about a finished task, a new condition, a change of plan, or a recent discovery may guide the interpretation more reliably than translation does.

Try applying the questions to these pairs:

• 他开了门。— He opened the door. (The opening is viewed as completed.)

• 门开了。— The door is open now. (The situation has changed.)

• 她走了。— She left. (Her leaving is presented as a completed event.)

• 她不走了。— She is not leaving anymore. (Her plan or situation has changed.)

• 我买了票。— I bought a ticket. (The purchase is complete.)

• 票贵了。— The ticket has become expensive. (Its current condition is different.)

The distinction is not a mechanical translation trick. It is a way of asking what the speaker has placed in the foreground: the endpoint of an event, or the transition into a new reality.

Finally, remember that 了 is not required every time English uses “did,” “has,” or “now.” Chinese speakers use context, time expressions, and the listener’s knowledge to avoid unnecessary markers. Your goal is therefore not to attach 了 to every past action. Instead, listen for the speaker’s viewpoint: Is this event being completed, or is this situation newly true? That question turns one intimidating particle into two manageable pieces of the Chinese timeline.

The question “Is this event being completed, or is this situation newly true?” gives us one useful way into 了. But Chinese has two other markers that shift the viewpoint in different directions. 过 looks backward across someone’s experience: it says that an event has happened at least once. 着 holds our attention on a condition that remains attached to a person or object.

Neither one is simply a Chinese equivalent of an English tense. They tell you how to frame the situation.

过: an experience on your life record

Compare these two sentences:

• 我去北京了。— I went to Beijing. / I have gone to Beijing.
• 我去过北京。— I have been to Beijing before.

The first sentence, with 了, presents a particular trip as a completed event or announces a new situation: perhaps the speaker has just arrived in Beijing, or is explaining what happened during a certain episode. The second sentence, with 过, does something more specific. It places “going to Beijing” on the speaker’s record of experience. The exact trip is not important; the fact that the experience exists is.

This is why 过 is often translated as “have ever,” “have before,” or “have had the experience of.”

• 你吃过北京烤鸭吗？— Have you ever eaten Beijing roast duck?
• 我看过这部电影。— I have seen this movie before.
• 他没去过中国。— He has never been to China.

The question is not usually “Did you eat it on Tuesday?” or “When did you see the movie?” It is “Does this experience belong to your background?” If the answer is yes, 过 is appropriate.

That experience can be repeated, and 过 does not by itself say whether it happened once or many times:

• 我去过三次上海。— I have been to Shanghai three times.
• 她吃过很多次火锅。— She has eaten hot pot many times.

A number or frequency expression can supply the detail. Without one, 我去过上海 simply means that Shanghai is somewhere the speaker has visited before.

过 and 了: event versus experience

The difference becomes clearer when the same verb appears with the two markers:

• 我看了那部电影。— I watched/saw that movie. (A particular viewing is complete.)
• 我看过那部电影。— I have seen that movie before. (The experience is already part of my background.)

You might say 我看了那部电影 when explaining last night’s schedule. You might say 我看过那部电影 when someone recommends it and you want to say, “I already know it.” The first sentence organizes an event; the second identifies an experience.

The markers can also appear together, but they contribute different ideas:

• 我去过北京了。— I have been to Beijing now / I’ve already had the experience of going to Beijing.

This combination is less neutral than either marker alone and depends heavily on context. 过 presents the experience; 了 can add a sense that this fact is now established, newly relevant, or has changed in the conversation. Do not treat the combination as a fixed formula. Listen for what each marker is doing.

There is also an important limitation: 过 normally describes an experience completed enough to be recognized as an experience. It is not the natural marker for an action currently in progress. For that, Chinese uses other structures, especially 在 or 正在, which we will distinguish from 着 below.

着: a condition that stays attached

While 过 looks backward over a person’s experience, 着 keeps a state in view. It commonly follows a verb and shows that the result or condition of that verb continues.

• 门开着。— The door is open.
• 灯亮着。— The light is on.
• 他穿着一件黑色的外套。— He is wearing a black coat.
• 她坐着等我。— She is sitting and waiting for me.

In 门开着, 着 does not mean “the door is opening.” The opening may have happened earlier; what matters now is the continuing condition: the door remains open. Likewise, 穿着 describes the condition of having clothes on, not necessarily the moment of putting them on.

This makes 着 especially common with posture, position, clothing, arrangement, and states that provide a background for another event:

• 墙上挂着一张地图。— A map is hanging on the wall.
• 桌子上放着两本书。— There are two books sitting on the table.
• 他笑着说：“没关系。”— He said, smiling, “It’s okay.”

In the last example, 笑着 tells us the manner or accompanying state in which he spoke. The smiling is not presented as a separate completed event. It is a condition accompanying the main action.

着 and 在: state versus action in progress

Learners often connect 着 and 在 because both may be translated with English “-ing.” But they answer different questions.

• 他在看书。— He is reading a book.
• 他戴着眼镜。— He is wearing glasses.

在 focuses on an activity underway. Reading is an event unfolding through time. 着 focuses on a state maintained while the sentence is being observed. Wearing glasses is not normally framed as an action unfolding; it is an attached condition.

The contrast is even clearer here:

• 她在开门。— She is opening the door. (The action is in progress.)
• 门开着。— The door is open. (The resulting condition continues.)

Similarly:

• 他在穿衣服。— He is getting dressed. (The action is underway.)
• 他穿着衣服。— He is wearing clothes. (The condition is in place.)

English often uses one broad “-ing” shape for both activity and state, so translation can conceal the difference. Chinese makes you ask whether you are watching something happen or observing the condition left in place.

Three viewpoints, not three past tenses

Put the markers side by side:

• 我看了这本书。— I read this book. (The reading is presented as complete.)
• 我看过这本书。— I have read this book before. (The experience is in my background.)
• 我在看这本书。— I am reading this book. (The activity is in progress.)
• 这本书放着。— This book is lying there / has been left there. (Its position remains.)

The markers do not form a simple past-present-future system. They are more like camera settings. 了 points toward completion or a newly changed situation. 过 pulls the camera back and asks whether the experience has ever occurred. 在 follows an activity as it unfolds. 着 keeps a continuing state or accompanying condition in the frame.

When you meet 过, ask: “Has this ever happened in the subject’s experience?” When you meet 着, ask: “What condition is being maintained or left in place?”

That habit will keep you from translating particles mechanically. Instead of searching for one English word, identify the speaker’s viewpoint—and let the surrounding context tell you why that viewpoint matters.

The same camera metaphor helps with negation. If 了, 过, and 着 show the speaker’s viewpoint on an event, 不 and 没（有） tell us how that event is being rejected. The crucial question is not simply “Which word means not?” but:

Is the speaker denying a general pattern or intention, or denying that an event has happened?

In everyday Mandarin, 不 usually looks forward or describes a rule, habit, preference, or stable judgment. 没（有） looks back toward the presence or absence of an event. It says that something has not happened, did not happen, or has not yet happened.

不: habits, choices, and what will not happen

Use 不 when the negation concerns a regular action, a present tendency, a decision, or a future intention:

• 我不喝咖啡。— I don’t drink coffee.
• 他不坐地铁。— He doesn’t take the subway.
• 我明天不去公司。— I’m not going to the office tomorrow.
• 她不想买那辆车。— She doesn’t want to buy that car.

These sentences do not normally report a completed event. They describe the subject’s pattern or position. 我不喝咖啡 may mean “I don’t drink coffee” as a general habit; it does not naturally mean “I didn’t drink coffee this morning.” For that specific past event, Mandarin normally uses 没（有）:

• 我今天早上没喝咖啡。— I didn’t drink coffee this morning.

The same distinction appears with future plans. 不 can deny an intention or expected action:

• 他不来了。— He isn’t coming. / He has decided not to come.
• 我下个月不去北京。— I’m not going to Beijing next month.

Here 不 is not describing a past failure to arrive. It presents the action as something that will not occur, often because of a choice or change of plan. The sentence-final 了 in 他不来了 signals a new situation: previously he may have been expected, but now the plan has changed.

没（有）: an event is absent

Use 没（有） when you deny that an event occurred or that a condition has been reached:

• 我没吃早饭。— I didn’t eat breakfast.
• 他没有看见我。— He didn’t see me.
• 他们还没到。— They haven’t arrived yet.
• 我没有去过成都。— I have never been to Chengdu.

The speaker is placing the event on the timeline and saying: it is not there. With 还没, the event remains possible or expected:

• 电影还没开始。— The movie hasn’t started yet.
• 我还没有决定。— I haven’t decided yet.

This is different from 不:

• 我不吃辣。— I don’t eat spicy food.
• 我没吃辣。— I didn’t eat spicy food.

The first describes a preference, habit, or policy. The second describes one occasion. A person could say both in sequence:

我不吃辣，昨天也没吃那道菜。

I don’t eat spicy food, and I didn’t eat that dish yesterday either.

Why 不 normally does not negate 了

A completed event marked with verb-final 了 is normally negated with 没（有）, and the 了 disappears:

• 我买了票。— I bought the ticket.
• 我没买票。— I didn’t buy the ticket.

Not usually:

• 我不买了票。

The problem is that 不 and completed-event 了 point in conflicting directions. 不 rejects an action as a habit, choice, or future possibility; 了 presents the action as completed or as having produced a new situation. To deny the event’s occurrence, Mandarin uses 没 instead.

The same pattern applies to 过:

• 我去过上海。— I have been to Shanghai.
• 我没去过上海。— I have never been to Shanghai.

Not:

• 我不去过上海。

Because 过 asks whether an experience exists in the subject’s past, 没（有） is the natural negator. It removes that experience from the record.

There is one important qualification. 不 can occur with a verb plus 了 when 了 marks a changed situation rather than the completion of a single past event:

• 我不喝了。— I’m not drinking anymore.
• 他不来了。— He isn’t coming after all.
• 她不吃肉了。— She doesn’t eat meat anymore.

Here 了 means “now the situation is different.” In 我不喝了, the speaker may have been drinking a moment ago but has stopped. This is not the same structure as denying a completed action. Compare:

• 我没喝酒。— I didn’t drink alcohol.
• 我不喝酒了。— I don’t drink alcohol anymore. / I’m not drinking alcohol now.

The first answers whether a drinking event occurred. The second announces a change in policy or current activity.

Negating experience, states, and ongoing events

With 过, use 没（有）:

• 你有没有看过这部电影？— Have you seen this movie?
• 我没有看过。— I haven’t seen it.

With 着, negation depends on what is being denied. If the sentence describes a state that is not currently in place, 没（有） is common:

• 门没开着。— The door isn’t open.
• 灯没有亮着。— The light isn’t on.

But if the speaker means a general habit or instruction, 不 may be appropriate:

• 他不穿着外套睡觉。— He doesn’t sleep wearing a coat.

In ordinary conversation, speakers may also avoid forcing a direct contrast with 着 and use a simpler adjective or verb: 门没开 can mean “The door isn’t open,” while 门没开着 emphasizes the continuing state.

For an action currently unfolding, 没在 means that the action is not happening:

• 他没在睡觉。— He isn’t sleeping.
• 我没在看电视。— I’m not watching television.

This is different from a habitual statement:

• 他不睡觉。— He doesn’t sleep. / He refuses to sleep. / He generally does not sleep.
• 他没在睡觉。— He is not sleeping right now.

Context decides how broad the time frame is, but the grammar gives you the first clue: 不 frames a pattern or stance; 没 removes an event or current occurrence from the picture.

A practical decision procedure

When you need to negate a sentence, pause before translating not. Ask three questions:

1. Am I describing a habit, preference, rule, or intention? Use 不.
2. Am I saying that a particular event did not happen, or that an experience has never occurred? Use 没（有）.
3. Am I describing a changed situation with 了? Both may appear, but their jobs differ: 没 denies an event; 不……了 announces that the situation has changed.

The contrast becomes clear in a small timeline:

• 我不去。 I’m not going / I don’t go.
• 我没去。 I didn’t go.
• 我不去了。 I’m not going after all.
• 我还没去。 I haven’t gone yet.
• 我没去过。 I’ve never been.

These are not five translations of one sentence. They are five different ways of placing the action in time and experience.

Correction practice

Correct the following sentences. First identify what the speaker means: a habit or intention, a completed event, an experience, or a changed situation. Then replace the incorrect negation or particle.

1. 我不吃了早饭。 — I didn’t eat breakfast.
2. 他不去过中国。 — He has never been to China.
3. 我没有喝咖啡。 — I don’t drink coffee. (The intended meaning is a general habit.)
4. 她不来了昨天。 — She didn’t come yesterday.
5. 我们不还没买票。 — We haven’t bought the tickets yet.
6. 我没去明天的会议。 — I’m not going to tomorrow’s meeting.

Possible corrections:

1. 我没吃早饭。 The breakfast event did not happen. The completed-event 了 is removed under 没.
2. 他没去过中国。 过 asks about experience, so its negation is 没（有）.
3. 我不喝咖啡。 This is a general preference or habit, not one missing occasion.
4. 她昨天没来。 The time expression can come first, and 没 denies the completed arrival.
5. 我们还没买票。 还没 means “not yet”; 不 is not needed.
6. 我明天不去会议。 More naturally, 我明天不去开会 or 我不参加明天的会议. The future intention is negated with 不.

One final test is especially useful. If you can naturally add 昨天, 刚才, or 到现在还, you are probably talking about whether an event occurred, so 没（有） is likely. If you can add 通常, 明天, 以后, or “as a rule,” 不 is likely. The words do not merely negate verbs; they select a different view of the event—one concerned with patterns and choices, the other with whether reality contains the event at all.