Learn Hardcore French: Il ne faut pas interrompre Marie quand elle parle. - One must not interrupt Marie when she is speaking.

Il faut roughly means one must / you must / it is necessary to.
The il is grammatical only; it doesn’t refer to a person or thing. You can think of it like the it in English it is raining—there is a subject grammatically, but it doesn’t refer to anything concrete.

So Il faut = It is necessary / One must / You have to + infinitive.

Why is interrompre in the infinitive form after il faut?

The structure with falloir is:

Il faut + infinitive

You always follow il faut with an infinitive when you are giving a general rule or obligation and not specifying a particular subject like je / tu / nous.

So:

Il faut interrompre = One must interrupt (general, rule-like)
Il ne faut pas interrompre = One must not interrupt

If you wanted a personal subject, you would change structure entirely, for example:

Tu ne dois pas interrompre Marie – You must not interrupt Marie.

Why are there two negative words, ne and pas, and why do they go around faut?

The basic French negation is:

ne + conjugated verb + pas

In this sentence, the conjugated verb is faut (from falloir), so:

Il ne faut pas interrompre…
ne and pas go around faut, not around interrompre, because faut is the main (conjugated) verb; interrompre is just an infinitive that follows it.

In everyday spoken French, people often drop ne and just say:

Faut pas interrompre Marie quand elle parle.

Why doesn’t the French sentence say “you” anywhere, like tu or vous?

The sentence uses il ne faut pas + infinitive, which expresses a general rule or obligation, not directed at a specific person.

In English we often express general rules with you:

You must not interrupt Marie when she speaks.

French uses the impersonal construction instead:

Il ne faut pas interrompre Marie… = One must not interrupt Marie… / You should not interrupt Marie… (general “you”)

If you really wanted to address a specific “you,” you’d change the structure and say:

Tu ne dois pas interrompre Marie quand elle parle.
Vous ne devez pas interrompre Marie quand elle parle.

Could we say On ne doit pas interrompre Marie quand elle parle instead? What’s the difference?

Yes, On ne doit pas interrompre Marie quand elle parle is correct and close in meaning.

Nuances:

Il ne faut pas interrompre…
– a bit more neutral/impersonal, like stating a rule or guideline.
On ne doit pas interrompre…
– also general, but feels a little more like “we / people in general / you” shouldn’t do it.

In many everyday contexts, they’re interchangeable. If you imagine a written rule (e.g., etiquette advice), Il ne faut pas… feels slightly more standard or textbook-like.

Could I say Je ne faut pas interrompre to mean “I must not interrupt”?

No, that is incorrect.

Falloir is almost always used only in the third person singular:

il faut / il ne faut pas

You do not conjugate it as je faut, tu faut, etc.

If you want to say I must not interrupt, you’d use a different verb:

Je ne dois pas interrompre. (from devoir = to have to, must)

Can I replace Marie with a pronoun? How would the sentence change?

Yes, you can replace Marie with a direct object pronoun la (her) or l’ before a vowel sound. With an infinitive, the object pronoun goes before the infinitive:

Il ne faut pas l’interrompre quand elle parle.
(Here l’ = la, referring to Marie.)

Word order with pronouns and this structure is:

Il ne faut pas + (object pronoun) + infinitive

So you cannot say Il ne faut pas interrompre la; the pronoun must come before interrompre.

Why is there no article (like la or une) before Marie?

Marie is a proper name, and in standard French you normally do not use an article before a person’s first name:

Marie parle. – Marie is speaking.
Il ne faut pas interrompre Marie.

In some regional or very informal varieties of French, people may say things like la Marie, but in standard French (and in writing, or for learners), you simply say Marie with no article.

Why is it elle parle and not just parle without a subject like in English “when speaking”?

In French, a subject pronoun is almost always required; you cannot usually drop it.

English can say: …when speaking.
French needs a subject for the verb: quand elle parle.

Here, elle clearly refers back to Marie, and French grammar requires that pronoun:

Marie → elle
quand elle parle = when she speaks / when she is speaking

Why is it quand elle parle and not quand elle est en train de parler for “when she is speaking”?

French often uses the simple present where English uses the present continuous (is speaking).

So:

quand elle parle can mean both:
- when she speaks (habitual)
- when she is speaking (at that moment)

You can say quand elle est en train de parler, but that’s heavier and more explicit, used when you really want to insist on the ongoing nature of the action. For a normal rule like this, quand elle parle is more natural.

Could we use lorsque instead of quand, as in lorsqu’elle parle?

Yes, you can say:

Il ne faut pas interrompre Marie lorsqu’elle parle.

Lorsque and quand are very close in meaning and often interchangeable when they mean when (in the temporal sense).

Nuances:

quand: more frequent, neutral, used in all registers.
lorsque: a bit more formal or literary; often preferred in writing but still common in speech.

In this sentence, both quand and lorsque are perfectly acceptable.

Why can’t we say something like Il ne faut pas quand elle parle interrompre Marie?

Word order in French doesn’t allow the quand-clause to be inserted in the middle of the verb phrase like that.

The typical and natural orders are:

Il ne faut pas interrompre Marie quand elle parle.
Quand elle parle, il ne faut pas interrompre Marie.

You keep:

Il ne faut pas together as the negated main verb structure.
interrompre Marie together as the verb + object.
quand elle parle as a separate time clause, which usually goes either at the beginning or at the end, not inside the main verb phrase.

How would this sound in everyday spoken French? Are there any common reductions?

In casual speech, several things often happen:

ne is dropped:
Faut pas interrompre Marie quand elle parle.
Pronunciation gets smoother:
- il ne faut pas → often sounds like something close to [i fopa] (and often without il in very casual speech: Faut pas…)
- quand elle → [kɑ̃tɛl], almost like one word.

But in writing, and for learners, it’s better to keep the full form:

Il ne faut pas interrompre Marie quand elle parle.