A coordinating conjunction links two elements of the same nature without merging them into a single group. It can unite two nouns, two adjectives, two verbs, two clauses or two ideas. In pain et fromage, the two words keep their identity. In il lit et il écrit, each verb remains in its own clause. Without the conjunction, the sentence yields two separate blocks. With it, the link becomes clear and direct. This type of link is often used to organize a statement before studying the more precise sense relationships in Conjonctions de Subordination.

Et adds an element to another. It connects two informations that go together, as in un café et un croissant, petit et rapide, je travaille et j’écoute de la musique. Ou presents a choice between two possibilities. In thé ou café, one option is kept. The structure remains the same: word + et + word, or word + ou + word. In a sentence, et accumulates, while ou selects. It is also found in oppositions of choices useful to talk about concrete possibilities, like tu viens en train ou en voiture.

Uses of and and or

Usage	Explanation
Addition of ideas	We use and to add an idea or an element without changing the meaning of the sentence.
Choice between possibilities	We use or to show that one must choose between two possibilities.

Mais links two ideas by marking a contrast. The second idea limits, corrects, or opposes the first: il veut sortir, mais il pleut. The first part signals an expectation, the second shifts it. Or serves to introduce an element that advances the discourse by bringing in new, often unexpected or decisive information: je voulais partir tôt, or le train était annulé. It does not merely juxtapose two facts; it creates a logical transition. Mais is common in everyday speech, while or appears mainly in more formal discourse, notably for chaining a reasoning, as seen also in Conjonctions adversatives.

Uses of but and or

Usage	Explanation
Opposition	We use mais to oppose two ideas in the same sentence.
Transition in discourse	We use or to introduce a nuance or a new fact that changes the rest of the discourse.

Donc signals a consequence. It links a known cause to a result: il pleuvait, donc nous sommes restés. The second proposition follows from the first. Car introduces a cause or an explanation: nous sommes restés car il pleuvait. With car, the reason is given after the main idea. The difference lies in the sense of the link. Donc pushes toward the effect, car brings back to the cause. In usage, donc often appears at the start of a clause or after a comma, while car directly links the explanation to what precedes. These two forms are very useful for expressing causal relationships, as in Conjonctions causales.

Uses of donc and car

Usage	Explanation
Consequence	We use donc to announce a logical consequence.
Cause or explanation	We use car to give the reason for what precedes.

Ni... ni... coordinates two negated elements at the same time. The structure allows refusing two possibilities, two objects, or two ideas in a single sentence: je ne veux ni café ni thé, il n’aime ni le bruit ni la foule. The first ni announces the first negated element, the second ni introduces the next. The main negation is done with ne, often accompanied by another negation marker depending on the sentence. Ni... ni... sits in front of the elements concerned and ties them in a single exclusion. This negative coordination also helps avoid repeating the same negation several times in a statement. It frequently appears in sentences where two options are rejected at once, as in the uses studied with the Conjonctions corrélatives.

Rules of negative coordination

Idea
We use ni...ni... to deny two elements at once.
We place ni before each of the denied elements.

The elements linked by a coordinating conjunction keep their own form. The conjunction does not modify them and does not change their gender, number, or person. One says un frère et une sœur, not a mixed form of the two words. One says il chante et danse, each verb staying in its place and in its form. The conjunction sits between the two elements it links, except in ni... ni..., where it frames the coordinated terms. It does not combine with the words to form a single word. In the sentence, it serves as a fixed hinge between the elements and leaves each intact, which also helps to understand the Word Order in the clause.

Rules of coordination and the invariable

Idea
Words linked by a coordinating conjunction keep their form.
The conjunction is placed between the coordinated words.