Mi dispiace, ma oggi non posso venire.

Because dispiacere works differently from English to be sorry.

Literally, mi dispiace means something like it causes displeasure/regret to me.

• mi = to me
• dispiace = is displeasing / causes regret

So Italian often expresses this idea as something is regrettable to me, rather than I am sorry.

That is why you say:

• Mi dispiace = I’m sorry

and not normally sono dispiace.

Because dispiacere is usually used in an impersonal-style pattern, similar to piacere.

In other words, the thing that causes regret is the grammatical subject, not the person feeling it.

For example:

• Mi dispiace = I’m sorry / It’s regrettable to me
• Mi dispiace la situazione = I’m sorry about the situation / literally The situation is regrettable to me

Io dispiaccio would mean something more like I cause displeasure, which is not what you want here.

Italian often drops subject pronouns when they are already clear from the verb form.

In non posso, the ending -o already tells you the subject is I:

• posso = I can

So:

• (io) non posso venire = I can’t come

Adding io is possible, but it usually adds emphasis:

• Io non posso venire = I can’t come / I’m the one who can’t come

In Italian, non normally goes directly before the conjugated verb to make it negative.

So:

• posso = I can
• non posso = I cannot / I can’t

This is the standard pattern:

• parlo → non parlo
• ho → non ho
• vengo → non vengo

So oggi non posso venire is the normal word order.

Because after a modal verb like potere (can / to be able to), Italian usually uses the infinitive directly, with no preposition.

So you say:

• posso venire = I can come
• voglio andare = I want to go
• devo studiare = I have to study

Not:

• posso a venire ❌

English learners often want to insert a preposition, but Italian does not do that here.

Venire means to come.

In this sentence:

• non posso venire = I can’t come

Italian distinguishes:

• venire = to come (toward the speaker or destination being discussed)
• andare = to go

So if someone invites you somewhere, venire is very natural:

• Puoi venire? = Can you come?

Oggi means today, and it is placed early in the sentence to set the time frame right away.

So:

• Mi dispiace, ma oggi non posso venire. = I’m sorry, but today I can’t come.

Italian is fairly flexible with adverb placement, but this order is very natural. It highlights today as the important limitation.

You might also hear:

• Mi dispiace, ma non posso venire oggi.

This is also correct, but it places oggi later. The original sentence emphasizes today a bit sooner.

Ma means but.

It connects the apology to the explanation:

• Mi dispiace = I’m sorry
• ma = but
• oggi non posso venire = today I can’t come

So the sentence has the same logic as in English:

• I’m sorry, but today I can’t come.

Yes. Mi spiace is a common shorter form of mi dispiace.

Both mean:

• I’m sorry

In general:

• Mi dispiace sounds a bit fuller and sometimes slightly more formal or careful.
• Mi spiace is very common in everyday speech.

So you could also say:

• Mi spiace, ma oggi non posso venire.

Yes, it is polite and completely natural.

Mi dispiace, ma oggi non posso venire works well in many situations, especially with friends, coworkers, or casual plans.

If you want to sound more formal or soften it further, you could say:

• Mi dispiace, ma oggi non posso venire.
• Mi dispiace, ma oggi non riesco a venire.
  (I’m sorry, but I can’t manage to come today.)
• Mi dispiace, ma oggi non potrò venire.
  (I’m sorry, but I won’t be able to come today.)

The original sentence is already polite and correct.

The comma separates the apology from the explanation:

• Mi dispiace,
• ma oggi non posso venire.

This is very natural in writing, just like in English:

• I’m sorry, but today I can’t come.

It also reflects a small pause in speech.

A natural pronunciation guide is:

Mee dee-SPYAH-cheh, mah OJ-jee non POS-so veh-NEE-reh.

A few helpful points:

• mi sounds like mee
• dispiace has the stress on -pia-
• oggi sounds roughly like OJ-jee
• posso has a clear double s, so it is more clipped than English pozo
• venire has the stress on -ni-

You do not need to pronounce it word-for-word mechanically; say it smoothly as one idea: Mi dispiace, ma oggi non posso venire.

Yes. Depending on context, it can naturally correspond to:

• I’m sorry, but I can’t come today.
• I’m sorry, but I can’t make it today.

The Italian sentence itself is straightforward and neutral. English may translate it in slightly different ways depending on the situation, but the core meaning stays the same.