Quand le ciel est clair, l’horizon semble plus large depuis le haut de la falaise.

Here quand introduces a time/condition clause: Quand le ciel est clair...

In English, it can feel like either when or whenever, depending on context. In this sentence, because the present tense is used for a general observation, it has a whenever / when(ever) this happens sense:

• Quand le ciel est clair, ... = When the sky is clear, ...
• idea: Whenever the sky is clear, the horizon seems wider

So it is not just about one single moment; it sounds like a general truth.

Because clair is being used as an adjective after the verb être.

• le ciel est clair = the sky is clear

This is the normal pattern:

• noun + être + adjective

If you put clair before ciel, as in le clair ciel, it would sound very literary, poetic, or unnatural in ordinary speech. In normal French, if you want to say the sky is clear, you say:

• le ciel est clair

Because horizon begins with an h muet in French, so the article le becomes l’ before it.

• le + horizon → l’horizon

This is called elision. French does this before a vowel sound or a silent h:

• l’horizon
• l’homme
• l’école

So the apostrophe is not optional here.

Horizon is masculine.

That is why the basic article is le horizon, which becomes l’horizon because of elision.

You can see its gender more clearly in other contexts:

• un horizon
• l’horizon est large
• ce bel horizon

Even though l’ does not show gender by itself, the noun is still masculine.

Semble is the third-person singular form of sembler, which means to seem.

The subject is l’horizon, which is singular, so French uses semble:

• l’horizon semble... = the horizon seems...

After sembler, French can use an adjective directly:

• sembler clair
• sembler étrange
• sembler plus large

So:

• l’horizon semble plus large = the horizon seems wider

Plus large is the comparative form:

• large = wide / broad
• plus large = wider / broader

French often leaves the comparison implicit if the context makes it obvious. So this sentence does not need to say exactly wider than what.

The implied meaning is something like:

• wider than usual
• wider than when the sky is not clear
• wider than it appears in other conditions

So semble plus large is a natural way to say seems wider even without stating the second term of the comparison.

Because large focuses more on width, breadth, or expanse.

For a horizon, that makes good sense: the horizon looks more spread out or expansive.

• large = wide, broad
• grand = big, large, tall, great in a more general sense

If you said plus grand, it would sound less precise here. Plus large matches the visual idea better: the horizon appears broader across your field of view.

This phrase gives the viewpoint.

• depuis = from
• le haut de la falaise = the top of the cliff

So:

• depuis le haut de la falaise = from the top of the cliff

It tells you where the observer is standing when the horizon seems wider.

Also, haut here is being used as a noun, meaning top or upper part:

• le haut de la falaise = the top of the cliff

Yes. Du haut de la falaise is also very natural, and many learners will hear that structure often.

There is a slight nuance:

• depuis le haut de la falaise emphasizes the point of view / place from which something is seen
• du haut de la falaise is a very idiomatic way to mean from the top of the cliff

So both can work, but du haut de la falaise may sound a bit more fixed and idiomatic in many contexts.

French uses definite articles more often than English does.

In this sentence, the nouns refer to things understood as part of a specific scene:

• the sky
• the horizon
• the cliff

French naturally says:

• le ciel
• l’horizon
• la falaise

Even when English might sometimes sound less definite, French often prefers the definite article for things that are general, familiar, or clearly identifiable in the situation.

French can put that clause either before or after the main clause.

• Quand le ciel est clair, l’horizon semble plus large...
• L’horizon semble plus large quand le ciel est clair...

Both are possible.

Putting Quand le ciel est clair first gives the sentence a nice structure: it sets up the condition before giving the result. In English, we do the same thing very often:

• When the sky is clear, ...

The comma after the opening clause is also normal here.

In plus large, plus is usually pronounced ply, without pronouncing the final s, because large begins with a consonant sound.

So it sounds roughly like:

• ply larzh

Compare:

• plus grand → usually ply gran
• plus intéressant → often ply.z‿ɛ̃.te.ʁe.sɑ̃ with liaison before a vowel sound

In this sentence, because large starts with l, the usual pronunciation is:

• plus large = ply large