Marie est sûre.

Because Marie is feminine singular, and adjectives in French agree with the person or thing they describe.

With sûr:

• masculine singular: sûr
• feminine singular: sûre
• masculine plural: sûrs
• feminine plural: sûres

So:

• Paul est sûr.
• Marie est sûre.

That e marks the feminine form of the adjective. It is very common in French for the feminine form to add a silent e.

In this word, the extra e changes the spelling, but not much in pronunciation. The final e itself is silent.

The accent is a circumflex: û.

In sûr / sûre, it is part of the correct spelling. It also helps distinguish the adjective sûr(e) from the preposition sur.

Compare:

• sûr / sûre = sure, certain
• sur = on

In modern French, they are usually pronounced the same, so the accent mainly matters in writing.

A common pronunciation is:

ma-REE eh syr

More exactly in IPA: /ma.ʁi ɛ syʁ/

A few useful notes:

• Marie = /ma.ʁi/
• est = /ɛ/
• sûre = /syʁ/

The u sound in French is not like English oo. To make it, try saying ee while rounding your lips.

Est is the third-person singular present of être (to be).

Since Marie is one person, French uses:

• je suis
• tu es
• il/elle est

So Marie est sûre follows the normal pattern: subject + être + adjective

It is an adjective.

It describes Marie, and it comes after the verb être. In this kind of sentence, French uses an adjective to describe the subject:

• Marie est sûre.
• Paul est heureux.
• Claire est prête.

So sûre is describing Marie’s state or quality.

Yes. Very often, sûr(e) is followed by:

• de + noun/pronoun
• que + clause

Examples:

• Marie est sûre de sa réponse.
• Marie est sûre de lui.
• Marie est sûre qu’il viendra.

If you just say Marie est sûre, it usually means Marie is sure, with the rest understood from context.

Yes. Certaine is also possible and often close in meaning.

• Marie est sûre.
• Marie est certaine.

Both can mean that Marie is certain. In many everyday situations, sûre is very common and natural. Certaine can sometimes sound a little more formal or a little more precise depending on context.

Sometimes, but you have to be careful.

French sûr(e) can mean sure/certain, and in some contexts it can also relate to safe/secure. However, if you want to say a person is physically safe, French often prefers expressions like:

• Marie est en sécurité.
• Marie est hors de danger.

So in a sentence like Marie est sûre, the most natural interpretation is usually that Marie is sure/certain, not that she is safe.

Because Marie is a proper name. In French, proper names normally do not take an article in simple sentences like this.

So you say:

• Marie est sûre.
• Paul est prêt.

not:

• La Marie est sûre. (except in some regional or special uses)

Yes. When an adjective describes the subject after être, it normally agrees in gender and number with that subject.

Examples:

• Marie est sûre.
• Paul est sûr.
• Marie et Anne sont sûres.
• Paul et Marc sont sûrs.

This is a very important French pattern.