Learn Hardcore French: Le professeur souligne la ligne importante dans mon cahier. - The teacher underlines the important line in my notebook.

For a male teacher:
- le professeur is used.
For a female teacher:
- You will hear both la professeure and la professeur in different regions and contexts.
When you speak in general about teachers (not specifying gender), French usually uses the masculine:
- Le professeur souligne la ligne importante… = The teacher underlines the important line… (teacher of unspecified gender).

So yes, if you are clearly talking about a female teacher, you might see la professeure souligne… in modern usage, but textbooks often stick to the traditional le professeur as a generic form.

What tense is souligne, and what is the infinitive form of the verb?

Souligne is the present tense, third person singular of the verb souligner.

Infinitive: souligner (to underline, to emphasize)
Present tense conjugation (singular forms):
- je souligne – I underline
- tu soulignes – you underline (informal singular)
- il / elle / on souligne – he / she / one underlines

In the sentence, le professeur is third person singular, so the verb is souligne.

Why is there no word like is (for “is underlining”) in the French sentence?

English distinguishes between:

He underlines the line. (simple present)
He is underlining the line. (present continuous)

French normally uses just one present tense form for both meanings:

Le professeur souligne la ligne importante…
can mean either
- The teacher underlines the important line…
  or
- The teacher is underlining the important line…

You usually do not add être (est) to form a progressive tense in standard French. Context tells you whether it is a general habit or something happening right now.

What is the direct object in this sentence?

The main structure is:

Le professeur – subject
souligne – verb
la ligne importante – direct object (the thing being underlined)
dans mon cahier – prepositional phrase showing location (where the line is)

So la ligne importante is the direct object of souligne.

You can check this by asking:
The teacher underlines what? → the important line.

Why does importante end with -e? How does agreement work here?

Importante is an adjective that must agree in gender and number with the noun it describes.

Noun: la ligne
- la shows it is feminine singular.
So the adjective important must also be feminine singular: importante.

Pattern for important:

Masculine singular: important – un livre important
Feminine singular: importante – une ligne importante
Masculine plural: importants – des livres importants
Feminine plural: importantes – des lignes importantes

In la ligne importante, both la and importante agree with ligne (feminine singular).

Why does the adjective importante come after ligne, not before it?

In French, most adjectives normally come after the noun they modify:

une voiture rouge – a red car
un film intéressant – an interesting film
la ligne importante – the important line

Some very common adjectives (often about beauty, age, goodness, size: beau, vieux, bon, grand, etc.) usually come before the noun:

un grand cahier – a big notebook
une bonne idée – a good idea

But important(e) is generally placed after the noun when it refers to importance in the normal sense:

une décision importante
la date importante
la ligne importante

So la ligne importante is the usual, natural word order.

Why is it mon cahier and not ma cahier, since cahier ends with -er?

In French, gender is a grammatical property of the noun, and you cannot guess it safely from the spelling.

cahier is masculine: le cahier.
Therefore you must use the masculine possessive mon:
- mon cahier – my notebook

Compare:

mon livre – my book (masculine: le livre)
ma table – my table (feminine: la table)

The ending -er does not make a word feminine.
You simply have to learn that cahier is masculine.

Why is the preposition dans used in dans mon cahier instead of sur mon cahier?

In English we say in my notebook, and French uses the same image: the line is inside the notebook, on one of its pages.

dans mon cahier = in my notebook (inside it, in its pages)

Sur usually means on (top of) something:

sur la table – on the table
sur le cahier – on top of the notebook (e.g. a pen lying on it)

So dans mon cahier is correct for writing or underlining something inside a notebook.

Does souligner only mean “to underline”, or can it also mean “to emphasize”?

Souligner has two main meanings:

Literal: to underline (draw a line under words on a page)
- Le professeur souligne la ligne importante.
  The teacher literally draws a line under it.
Figurative: to stress, to highlight, to emphasize
- Il a souligné l’importance de ce point.
  He emphasized the importance of that point.

In your sentence, because of la ligne and cahier, the most natural reading is the literal one (physically underlining a line in a notebook). But in other contexts, souligner often means to emphasize.

Can I say Le prof souligne la ligne importante instead of Le professeur souligne…?

Yes, but the tone changes.

Le professeur is more formal and neutral, typical of written French or textbooks.
Le prof is informal / colloquial, like the teacher vs the teacher/teach in everyday speech. It sounds more like how students talk about their teacher.

Both are grammatically correct; just choose based on the level of formality you want.

What exactly does cahier mean? Is it a notebook, an exercise book, or something else?

Cahier is usually:

a notebook (blank or lined pages)
an exercise book used at school
any kind of bound or stapled set of pages used for writing, exercises, notes, etc.

So dans mon cahier could be:

in my notebook
in my exercise book

The exact English translation depends on the context (school, personal notes, etc.), but notebook is a good general choice.

What is the difference between ligne and phrase in French? Why is it ligne here?

In French:

ligne = line (a physical line of text on a page)
- la première ligne du texte – the first line of the text
phrase = sentence (a grammatical unit, from capital letter to period)
- une phrase complète – a complete sentence

In your sentence:

la ligne importante dans mon cahier means the important line in my notebook – a specific line on the page.
If you said la phrase importante, it would mean the important sentence, focusing on the sentence as a grammatical unit, not just where it appears on the page.

Because the teacher is underlining a line in a notebook, ligne is the appropriate word.

Could I replace la ligne importante with a pronoun? How would that work?

Yes. If la ligne importante is already known from context, you can replace it with the direct object pronoun la (feminine singular).

Full form:
- Le professeur souligne la ligne importante dans mon cahier.
With pronoun:
- Le professeur la souligne dans mon cahier.
  → la replaces la ligne importante

Word order rule: in French, object pronouns like la go before the verb in simple tenses:

Le professeur la souligne. – The teacher underlines it.