Identifying the Sentence Subject in French

The subject is the noun or pronoun in a clause or sentence that performs the action of the verb. To find the subject, ask who or what is performing the action of the verb. It is crucial to recognize the subject because French verbs are conjugated according to the number, person and gender of the subject noun or the subject pronoun.

David lave la voiture. / David is washing the car.

Who is washing the car? David is, so David is the subject.

Subject Pronouns

Subject pronouns replace the specific names of people or things:

SINGULAR

•   1st person   je > I
•    2nd person  tu > you
•    3rd person   il > he, it / elle > she, it / on > one

PLURAL

•   1st person   nous > we
•    2nd person  vous > you
•    3rd person   ils > they (m) / elles > they (f)

The French subject pronoun on is an indefinite pronoun that means "one," "we," "you" and "they." It's often equivalent to the English passive voice.

  On ne devrait pas poser cette question.One shouldn't ask that question. / You shouldn't ask that quesiton.

Note that, unlike the English "I," the French je is only capitalized when it begins a sentence; otherwise it is lowercase.

Subjects in Sentences

Whether sentences be statements, exclamations, questions, or commands, there is always a subject, either stated or implied. Only in a command is the subject not explicitly stated; it is implied by the imperative conjugation of the verb.

Sentences can be separated into a subject (un sujet) and a predicate (un prédicat). The subject is the person or thing performing the action, and the predicate is the rest of the sentence, which usually begins with the verb.
Je suis professeur. 
Suject: Je. Prédicat: suis professeur.

I am a teacher
Subject: I. Predicate: am a professor.

La jeune fille est mignonne 
Sujet: La jeune fille. Prédicat: est mignonne. 

The young girl is cute.
Subject: The young girl. Predicate: is cute.