Learn Hardcore French: Ses boucles d’oreilles sont moins lourdes que celles d’hier. - Her earrings are less heavy than yesterday’s.

ses boucles d’oreilles = his/her earrings
It agrees with the thing owned, not with the owner.
- ses is plural because boucles d’oreilles is plural.
ces boucles d’oreilles would mean these earrings (demonstrative, not possessive).
les boucles d’oreilles would mean simply the earrings, with no idea of possession.

So ses tells us they belong to “him/her” (context decides which).

Why is boucles d’oreilles plural in French?

In French, une boucle d’oreille is one earring, and des boucles d’oreilles is earrings.

You normally wear two, so people usually speak in the plural:

Ses boucles d’oreilles = her/his earrings (both ears)
If you really mean only one: sa boucle d’oreille = his/her earring

The expression boucles d’oreilles is literally ear loops and is almost always used in the plural when you talk about someone’s earrings.

Why is lourdes feminine plural?

The adjective lourd / lourde (heavy) must agree with the noun boucles d’oreilles.

boucle is feminine: une boucle
boucles d’oreilles is feminine plural

So:

singular feminine: une boucle lourde
plural feminine: des boucles lourdes

In the sentence, lourdes is feminine plural to match ses boucles d’oreilles.

How does the comparative moins … que work here?

Moins … que is the standard structure for less … than:

moins lourd(e)(s) que = less heavy than

Pattern:

sujet + verbe + moins + adjectif + que + complément
Ses boucles d’oreilles sont moins lourdes que celles d’hier.
= Her earrings are less heavy than yesterday’s (ones).

You can use the same pattern with other adjectives:

Il est moins grand que son frère. = He is less tall than his brother.
C’est moins intéressant que le film d’hier. = It’s less interesting than yesterday’s film.

What exactly is celles here, and why not ceux or celles-ci?

Celles is a demonstrative pronoun: it stands for a previously mentioned feminine plural noun.

celles = the ones (feminine plural)
It replaces les boucles d’oreilles from the comparison:
… moins lourdes que celles d’hier
= … less heavy than the ones from yesterday.

Choice of form:

masculine plural: ceux
feminine plural: celles
masculine singular: celui
feminine singular: celle

We use celles because boucles (d’oreilles) is feminine plural.

Forms like celles-ci / celles-là add “these / those”, but here we don’t need here/there, just the ones.

Why do we say celles d’hier and not les d’hier?

In French, you cannot normally say les d’hier to mean yesterday’s ones. You need a pronoun that can stand alone.

celles d’hier = the ones from yesterday / yesterday’s ones
celles replaces les boucles d’oreilles
d’hier specifies from yesterday

Compare:

Ses boucles d’oreilles sont moins lourdes que celles d’hier.
✔ natural and correct
Ses boucles d’oreilles sont moins lourdes que les d’hier.
✘ incorrect in standard French

What is the function of d’ in d’hier?

D’ is a contracted form of de before a vowel sound.

In celles d’hier:

de roughly means of / from
hier means yesterday
d’hier together means from yesterday or yesterday’s

So celles d’hier is literally the ones of yesterday → yesterday’s ones.

Could we say ses boucles d’oreille in the singular here?

Grammatically you can say:

sa boucle d’oreille = his/her earring (one single earring)

But in this context, we are comparing the pair of earrings worn today with the pair worn yesterday, so we naturally use the plural:

Ses boucles d’oreilles sont moins lourdes que celles d’hier.

If you were talking about only one earring (for example, someone who only wears one), you could say:

Sa boucle d’oreille est moins lourde que celle d’hier.
(His/her earring is less heavy than yesterday’s one.)

Why is the structure sont moins lourdes que … and not sont moins que lourdes?

In French, the comparative moins normally goes directly before the adjective:

moins lourdes (less heavy)
moins intéressants (less interesting)
moins cher (cheaper / less expensive)

The order sont moins que lourdes would sound very unnatural and is not how the comparative works.

Correct pattern:

être + moins + adjectif + que
Elles sont moins lourdes que celles d’hier.

Could we replace moins lourdes with plus légères? Is there a difference?

Yes, you could say:

Ses boucles d’oreilles sont plus légères que celles d’hier.
= Her earrings are lighter than yesterday’s (ones).

Both are grammatically correct:

moins lourdes = less heavy
plus légères = lighter

In most contexts they mean the same thing, but there can be a small nuance:

moins lourdes focuses on the reduction of heaviness (maybe they were very heavy before).
plus légères emphasizes lightness as a positive quality.

In everyday speech, both are perfectly natural.