Causal conjunctions connect a consequence to its reason. They answer the question why? and introduce the idea that explains a fact, an action or a state. In Il reste à la maison parce qu’il est malade, the cause is the illness and the consequence is staying at home. If you remove the causal conjunction, the two ideas remain separate and the logical link disappears. A causal conjunction is therefore used to construct a sentence where the second clause gives the motive of the first. It is very useful for organizing a clear explanation, as in the sentences that are also found with the Conjonctions de Subordination.

Neutral usage of cause in speech

Usage	Explanation
Spontaneous response	We use « parce que » to give the simplest and most natural cause in a common response.
Direct link	We choose « parce que » when we want to directly connect an action to its cause without a particular tone.
Familiar explanation	We use « parce que » in an ordinary explanation, especially in speech or in a simple message.

Parce que is the most common causal conjunction. It introduces a complete clause and gives a direct, simple and neutral cause. We say Je pars parce que je suis fatigué, Elle sourit parce qu’elle a reçu une bonne nouvelle. The clause with parce que most often comes after the main clause, because it explains what has just been stated. In speech, it is the most natural form to answer a question or justify an action. In a chain of sentences, it functions as a classic subordination conjunction: main clause + parce que + complete clause.

Cause already known or obvious

Usage	Explanation
Admitted cause	We use « puisque » when the cause is already known or easily accepted by the listener.
Shared fact	We choose « puisque » to rely on a fact that everyone sees or recognizes.
Calm justification	We use « puisque » to justify a decision without giving the impression of defending oneself.

Puisque presents a cause considered as known, visible or already admitted by the other person. It is used when we do not discover the reason, but we recall it. Puisque tu es déjà prêt, on peut partir, Puisque le magasin est fermé, nous reviendrons demain. The sentence with puisque can precede or follow the main clause, but it often serves to start from a shared observation. The tone is more explanatory than parce que. In a conversation, puisque can also reinforce an obviousness, as in the Conjonctions de Coordination when one marks a logical relation between two ideas, but here the relation is causal.

Cause announced before the consequence

Usage	Explanation
Beginning of sentence	We put « comme » at the beginning when we want to announce the cause first, before the rest of the sentence.
More formal style	We use « comme » at the head of the sentence to give a more elegant or more written tone.
Introductory effect	We choose « comme » to prepare the main idea with a cause already posed from the start.

Comme introduces the cause at the start of the sentence. It first announces the reason, then the consequence. We say Comme il pleuvait, nous sommes restés chez nous or Comme tu n’as pas de billet, tu ne peux pas entrer. This position at the beginning gives a more formal or more polished style than parce que. The first clause explains the situation before the main action appears. Comme does not start a short answer on its own; it is used to establish the context from the opening of the sentence.

Explanation written

Usage	Explanation
Written register	We reserve « car » for a more written or more thoughtful register than spontaneous conversation.
Developed justification	We use « car » to give a calm explanation that supports the main idea.
Unnatural reply	We avoid « car » in a short and lively answer, as it often sounds too formal.

Car serves to introduce a justification, especially in writing. It connects two clauses and explains a previous statement: Je ne viendrai pas, car je suis malade. The tone is calmer than parce que. Car is not used at the start of a spontaneous answer and it remains less natural in ordinary spoken language. It is often found in explanatory text, an opinion, a letter or an argued sentence. It functions as a logical connective word, close to conjunctions of contrast by its place in discourse, but here it expresses a cause, not an opposition.

Formal and precise cause

Usage	Explanation
Administrative context	We use « étant donné que » for a formal cause, especially in an official or precise text.
Long explanation	We choose « étant donné que » when we want to present a cause with a more developed and organized tone.
Motivated decision	We use « étant donné que » to justify a decision based on a clearly established situation.

Étant donné que presents a cause as a given fact. The construction is more formal and often more administrative or explanatory. We say Étant donné que le dossier est incomplet, la demande est refusée or Étant donné que la route est fermée, il faut prendre un autre chemin. This expression generally occupies the beginning of the sentence and prepares a logical conclusion. It is well suited to announcements, reports, instructions and formal explanations. It gives a strong cause, presented as an objective datum.

Placement and form of the cause

Idea
The causal proposition can come before or after the main proposition.
After a causal conjunction, one uses a complete proposition with a subject and a verb.
When the cause is placed at the start, one often marks a pause with a comma.

A causal conjunction always connects a full clause to another full clause. After parce que, puisque, comme, car or étant donné que, there is a subject and a verb. We say Il est parti parce qu’il avait un rendez-vous, and not a simple sequence of isolated words. The order can change depending on the conjunction. With parce que and car, the cause often comes after the main clause. With comme and étant donné que, the cause is frequently placed before. With puisque, both positions exist depending on the intended effect. This organization well prepares structures of Propositions et Subordonnées.

Choice according to the role of the cause

Idea
We choose the real cause when we want to show the exact motive of a fact.
We choose an explanation when we mainly want to help the listener understand the situation.
We choose a justification when we want to defend or support a decision.

A real cause explains why something happens. Il est resté à l’intérieur parce qu’il neigeait presents a concrete fact. An explanation reformulates a situation to make it clear. Le bus est en retard, parce qu’il y a des travaux gives the reason without trying to persuade. A justification defends a decision or an opinion. Je refuse, car je n’ai pas assez d’informations supports a position. The choice of the conjunction depends on the desired link. Parce que remains neutral and very common. Puisque relies on an evident fact. Car is well suited to justification. Comme and étant donné que place the cause in a more formal frame.