wǒ jīntiān xiàwǔ yào shàng kè, suǒyǐ bù néng qù gōngyuán.

Chinese usually puts time expressions before the main verb.

A very common pattern is:

Subject + Time + Verb Phrase

So in:

我今天下午要上课

the order is:

• 我 = I
• 今天下午 = this afternoon
• 要上课 = am going to have class / need to attend class

This is one of the biggest differences from English. In English, time can move around more freely, but in Chinese it often comes before the verb.

Yes. That is completely natural.

Both are fine:

• 我今天下午要上课
• 今天下午我要上课

The difference is mostly about emphasis:

• 我今天下午要上课 emphasizes I
• 今天下午我要上课 emphasizes this afternoon

Chinese is flexible with sentence-opening elements like time words, as long as the sentence remains clear.

Here, 要 does not mainly mean want. In this sentence, it means something like:

• am going to
• need to
• have to
• be scheduled to

So 要上课 means have class, need to attend class, or am going to class.

Context matters a lot with 要:

• 我要咖啡 = I want coffee
• 我要上课 = I am going to have class / I need to attend class

So yes, 要 can mean want, but in this sentence it is more about a planned or necessary action.

Yes, 上 often means up or on, but in Chinese many verbs have extended meanings.

In 上课, 上 means something like:

• attend
• go to
• be in

So:

• 上课 = attend class / have class
• 上学 = go to school
• 上班 = go to work

This is very normal in Chinese. You should learn 上课 as a set phrase rather than translating each character too literally.

Usually, 上课 means to be in class or to attend class.

For a student:

• 我要上课 = I have class / I need to go to class

For a teacher, 上课 can sometimes also refer to giving a class, depending on context, but for most learners the safest first meaning is attend class / have class.

If you want to be very clear about teaching, Chinese often uses:

• 教课
• 给学生上课

所以 means so, therefore, or that’s why.

It connects the reason and the result:

• 我要上课 = I have class
• 所以不能去公园 = so I can’t go to the park

It works very much like English so.

A full reason-result pattern in Chinese is often:

因为 ... 所以 ... = because ... so ...

In your sentence, the 因为 part is omitted, which is very common:

• 我今天下午要上课，所以不能去公园。

You could also say:

• 因为我今天下午要上课，所以不能去公园。

Both are natural.

Both are correct.

• 所以不能去公园
• 所以我不能去公园

Chinese often omits the subject when it is already obvious from context.

Since the subject is already 我 in the first clause, repeating it is optional.

So:

• 我今天下午要上课，所以不能去公园。
• 我今天下午要上课，所以我不能去公园。

Both are natural. The version without the second 我 sounds a little more concise.

These mean different things.

• 不去公园 = not going to the park / won't go to the park
• 不能去公园 = cannot go to the park

In your sentence, the speaker is giving a reason: class makes going to the park impossible or not feasible. So 不能 is better because it expresses cannot.

Compare:

• 今天我不去公园。
  Today I’m not going to the park.
  (simple decision or statement)

• 今天我有事，不能去公园。
  I have something to do today, so I can’t go to the park.
  (there is a constraint)

Both can be translated as cannot, but they are not always the same.

• 不能 often means be unable to, not be in a position to, or cannot due to circumstances
• 不可以 often means not allowed to

In this sentence, the speaker has class, so the problem is circumstance, not permission. That is why 不能 is the better choice.

Examples:

• 我今天很忙，不能去。
  I’m busy today, so I can’t go.

• 这里不可以抽烟。
  You may not smoke here. / Smoking is not allowed here.

In Chinese, the destination usually comes after the verb 去.

Pattern:

去 + place

So:

• 去公园 = go to the park
• 去学校 = go to school
• 去北京 = go to Beijing

This is very straightforward. Unlike English, Chinese does not need a separate word like to here.

Chinese does not use articles like a, an, and the the way English does.

So 公园 can mean:

• a park
• the park
• parks

The exact meaning depends on context.

In this sentence, English naturally translates it as the park, but Chinese just says 公园.

This is normal and very important for English speakers to get used to.

Yes, but the meaning shifts a little.

• 我要上课 = I have class / I need to attend class
• 我要去上课 = I’m going to go attend class

Adding 去 makes the movement more explicit. Without 去, the sentence focuses more on the event or obligation itself.

In your original sentence, 我要上课 sounds very natural because the main point is I have class, not the physical act of going there.

Yes. This sentence pattern is very productive.

Examples:

• 我明天要上课，所以不能去公园。
  I have class tomorrow, so I can’t go to the park.

• 我晚上要上课，所以不能去公园。
  I have class tonight, so I can’t go to the park.

• 我周末要上课，所以不能去公园。
  I have class on the weekend, so I can’t go to the park.

This is a good sentence structure to memorize: 我 + time + 要 + verb, 所以 + 不能 + verb

It is helpful to think of it as both:

• 今天 = today
• 下午 = afternoon

Together:

• 今天下午 = this afternoon / this afternoon today

Chinese often stacks time words from larger time to smaller time:

• 今天下午三点 = 3 p.m. this afternoon
• 明天早上 = tomorrow morning

So yes, 今天下午 functions as one time phrase, but it is built from smaller time units.

Because 能 is usually negated with 不, not 没.

So:

• 不能 = cannot
• not 没能 in this sentence

没能 does exist, but it usually means did not manage to and often refers to something that failed to happen in the past.

Compare:

• 我今天不能去公园。
  I can’t go to the park today.

• 我昨天没能去公园。
  I wasn’t able to go to the park yesterday.

So in your sentence, 不能 is exactly right.

Yes, it helps show the pause between the two clauses:

• 我今天下午要上课
• 所以不能去公园

The comma makes the logic easier to read: first the reason, then the result.

In casual writing, punctuation can vary, but this comma is standard and helpful.

Yes. Chinese often leaves out connecting words when the relationship is obvious.

You could say:

我今天下午要上课，不能去公园。

That still sounds natural and clearly means:

I have class this afternoon, so I can’t go to the park.

Adding 所以 makes the cause-and-result relationship more explicit.

A useful way to see it is:

Subject + Time + 要 + Verb Phrase, 所以 + 不/不能 + Verb Phrase

In this sentence:

• 我 = subject
• 今天下午 = time
• 要上课 = planned/required action
• 所以 = so
• 不能去公园 = result: cannot go to the park

So the full pattern is:

I + this afternoon + have class, so + cannot + go to the park.

This is a very common and practical sentence pattern in Mandarin.