In a French sentence, coordination links two clauses of the same level. Each clause can function alone, and the conjunction merely places them side by side. With subordination, one clause depends on the other. It does not convey a complete idea by itself and serves to specify a cause, a time, a condition, a purpose, or a consequence. In Propositions et Subordonnées, this difference appears clearly: coordination adds, opposes, or chooses, while subordination organizes the information around a main clause.

After a subordinating conjunction, one expects a complete clause with a subject and a conjugated verb. Parce que Marie est fatiguée, quand il arrive, si tu veux. In each case, the part that follows the conjunction is not a simple group of words, but a real clause. The verb can be in a simple tense or in a compound tense, and the subject can be a noun, a pronoun or a noun phrase. Without a subject and with no conjugated verb, there is no subordinate clause.

Parce que presents a cause, quand situates a fact in time, and si marks a condition or an indirect question depending on the context. These conjunctions serve to link two clauses without placing them at the same level. In Je pars parce que je suis malade, the second clause explains the first. In Quand il pleut, je reste à la maison, it situates the action. In Si tu viens, nous mangerons ensemble, it sets the condition. The link between the two clauses is part of the meaning of the entire sentence.

To state the cause, the subordinate clause explains why the main action exists or occurs. You often find parce que, puisque, comme and étant donné que. Parce que introduces the most direct reason: Je rentre parce que je suis fatigué. Puisque presents a cause already known or obvious: Puisque tu es là, commence. Comme often places the cause at the beginning of the sentence: Comme il neige, les écoles ferment. These conjunctions link a reason to its result in Conjonctions causales.

The subordinate clause of purpose indicates the objective aimed at by the action of the main clause. We often use pour que, afin que, de peur que and de sorte que. The main clause describes the action accomplished, and the subordinate clause states the intention. Je parle lentement pour que tu comprennes shows the aim of speaking slowly. Il ferme la fenêtre afin que le bruit diminue shows the sought result. The verb in the subordinate clause follows the logic of the objective, not that of a simple fact already realized.

The condition makes the main clause depend on a possible, probable or imaginary situation. Si is the most frequent conjunction: Si tu as faim, prends une pomme. The main clause describes what will happen, would happen, or would be true if the condition is fulfilled. The subordinate clause can also begin with à condition que, pourvu que or à moins que depending on the degree of dependence. The overall meaning rests on the link between the condition and the consequence. To review the difference between cause, time and condition, compare with Conjonctions de Coordination and the other logical links of the sentence.

In a time subordinate clause, the choice of the verb depends on the temporal relationship with the main clause. Quand il arrive, nous partons places the two actions in the same temporal frame. Quand il sera arrivé, nous partirons shows that one action will be completed before the other. Avant que and jusqu’à ce que introduce a waiting or a limit, and the verb expresses this relationship precisely. The tense is chosen not only for the action itself, but for its position in the chronology of the sentence.

Relative clauses add information about a noun already present in the sentence. Qui replaces the subject of the relative clause: La femme qui parle est professeure. Que replaces the object: Le livre que j’ai acheté est cher. Dont takes a complement introduced by de: L’ami dont je parle habite ici. The relative clause is not used to link two independent ideas, but to specify a noun. It retains a very stable place in the sentence and attaches directly to the noun phrase it describes.

Some subordinate clauses placed at the beginning of the sentence create emphasis. Quand il arrive, tout change first gives the temporal frame, then the main information. Parce qu’il pleuvait, nous sommes restés foregrounds the cause. This arrangement draws attention to the logical relation before presenting the result. The reverse order, with the main clause first, keeps the focus on the main action. The choice depends on what the speaker wants to put first in the sentence.