Paul s’abstient aujourd’hui.

Because the verb is s’abstenir, which is a pronominal verb. That means it normally appears with a reflexive pronoun:

• je m’abstiens
• tu t’abstiens
• il / elle / on s’abstient
• nous nous abstenons
• vous vous abstenez
• ils / elles s’abstiennent

So in Paul s’abstient aujourd’hui, the s’ is not optional. It is part of the verb form.

In English, we usually just say Paul abstains today, without a reflexive word, but French uses the pronominal structure here.

The full pronoun is se, but before a vowel sound it contracts:

• se + abstient → s’abstient

French does this very often to avoid a clash of vowel sounds:

• je aime → j’aime
• se appelle → s’appelle
• me ennuie → m’ennuie

So s’abstient is just the normal shortened spelling before a.

It is the present tense: he abstains or he is abstaining, depending on context.

Here, Paul s’abstient aujourd’hui means that this is what Paul is doing today.

The infinitive is s’abstenir.
This particular form, s’abstient, is the 3rd person singular present.

Here is the full present-tense conjugation:

• je m’abstiens
• tu t’abstiens
• il / elle / on s’abstient
• nous nous abstenons
• vous vous abstenez
• ils / elles s’abstiennent

A useful thing to notice is that it behaves a lot like tenir and venir in some forms:

• je tiens → je m’abstiens
• il tient → il s’abstient

So if you already know verbs like tenir, this pattern may feel familiar.

A careful pronunciation is roughly:

Paul s’abstient aujourd’hui
[pɔl sapstjɛ̃ oʒuʁdɥi]

A few key points:

• Paul sounds roughly like pole, but with a French vowel.
• s’ is pronounced like s before the next word.
• In abstient, the final -t is silent.
• The ending -ient here gives a nasal sound, roughly -yain / -yen.
• aujourd’hui is roughly oh-zhoor-dwee.

There is no pronounced final t in abstient before aujourd’hui.

Very often, yes. French commonly uses s’abstenir de + infinitive or s’abstenir de + noun:

• Paul s’abstient de boire. = Paul is abstaining from drinking.
• Elle s’abstient de commenter. = She is refraining from commenting.

But the object can be left unstated if the context already makes it clear. So:

• Paul s’abstient aujourd’hui.

is grammatical, but by itself it may feel a little incomplete unless everyone already knows what he is abstaining from.

So this sentence is fine, but in real conversation French speakers often specify the thing.

It means to abstain, to refrain, or to deliberately not do something.

It usually suggests a conscious decision to hold back from an action. So it is often a bit more deliberate or formal than simply saying he doesn’t do it.

Depending on context, it can refer to things like:

• drinking
• eating something
• voting
• commenting
• taking part in something

So Paul s’abstient aujourd’hui suggests that Paul is intentionally refraining today.

Yes, aujourd’hui can move around.

The version you have:

• Paul s’abstient aujourd’hui.

is completely natural.

You could also say:

• Aujourd’hui, Paul s’abstient.
• Paul aujourd’hui s’abstient. (less common, more marked)

Putting aujourd’hui at the end is a very normal default word order.
Putting it at the beginning often adds a little emphasis to today.

Because aujourd’hui is an adverb meaning today. It does not take an article.

So French says simply:

• aujourd’hui = today

not something like le aujourd’hui.

It is just a fixed time expression.

For the negative, put ne ... pas around the conjugated verb:

• Paul ne s’abstient pas aujourd’hui. = Paul is not abstaining today.

Notice the order:

• ne + reflexive pronoun + verb + pas

For a yes/no question, common options are:

• Paul s’abstient aujourd’hui ?
  (spoken, rising intonation)
• Est-ce que Paul s’abstient aujourd’hui ?
• Paul s’abstient-il aujourd’hui ?
  (more formal)

It is definitely correct and common, but it can sound a bit formal or specific, depending on context.

For example, French often uses s’abstenir in:

• formal instructions: Merci de vous abstenir
• voting: Il s’est abstenu lors du vote
• deliberate restraint: Elle s’abstient de répondre

In everyday speech, if the meaning is more specific, people often choose a more direct verb instead:

• Paul ne boit pas aujourd’hui.
• Paul ne mange pas ça aujourd’hui.
• Paul ne participe pas aujourd’hui.

So Paul s’abstient aujourd’hui is grammatical, but in real life speakers often prefer a more precise sentence if they know what Paul is abstaining from.