Why are days of the week not capitalised in French?

French treats days, months and language names as common nouns rather than proper nouns. They behave the same way as any ordinary noun: capitalised only at the start of a sentence or in a title. Writing 'Lundi' mid-sentence is wrong in French even though the same word capitalised would be correct in English. The same rule covers months (janvier, février) and language names (anglais, français). It is the single most common spelling error English speakers make in written French.

What is the difference between lundi and le lundi?

Bare lundi refers to a specific Monday, usually this coming Monday or last Monday depending on context. Le lundi with the definite article refers to Mondays in general, the habitual sense. 'Lundi je vais à Paris' means 'this Monday I am going to Paris'; 'le lundi je vais à la piscine' means 'on Mondays I go to the pool'. The same distinction in Spanish is handled by singular vs plural (el lunes / los lunes); French does it with article presence.

Why did French children have Wednesday off school?

Wednesday was kept clear in primary schools historically so that families could send children to religious instruction without it competing with the secular school timetable, a compromise that dates back to the late nineteenth century separation of church and state. Over time the day off was extended to allow music lessons, sport, scouting and other activities, and mercredi became a fixture of French childhood culture. The 2013 reform restored Wednesday morning classes in most regions, but mercredi after-school activities still anchor the social rhythm.

What are the French abbreviations for days of the week?

The standard three-letter abbreviations are lun., mar., mer., jeu., ven., sam., dim. for lundi through dimanche. On calendars and timetables you also see single letters: L, M, M, J, V, S, D. The two Ms are genuinely ambiguous, and column position is usually the only thing telling you which is mardi and which is mercredi. Some calendars use Me. for mercredi to disambiguate.

Days of the Week in French

The seven days are lundi, mardi, mercredi, jeudi, vendredi, samedi, dimanche. They map almost perfectly onto Roman planetary gods, they start the week on Monday rather than Sunday, and they are written in lowercase even mid-sentence. This article covers all three of those features, the article-presence distinction that separates a specific Monday from a habitual one, the abbreviations, and the small cultural rhythms (mercredi off, vendredi soir) that change what these words actually mean in use.

The seven days

Day	Pronunciation	Etymology
lundi	luhn-DEE	Lunae dies, day of the Moon (Luna)
mardi	mar-DEE	Martis dies, day of Mars
mercredi	mair-kruh-DEE	Mercurii dies, day of Mercury
jeudi	zhuh-DEE	Jovis dies, day of Jupiter (Jove)
vendredi	von-druh-DEE	Veneris dies, day of Venus
samedi	sam-DEE	Sambati dies, day of the Sabbath
dimanche	dee-MONSH	Dominicus dies, the Lord's day

Five of the seven are Roman planetary gods, in the same order as Spanish (lunes, martes, miércoles, jueves, viernes) and the same Latin roots that show up in English Tuesday through Saturday (Tiw, Woden, Thor, Frigg, Saturn were substituted for the Roman gods in the Germanic naming, but the slot positions match). The shift at the end of the week is the Christian one: samedi comes from the Hebrew sabbath via Latin, and dimanche replaces what would have been "Solis dies" with the Lord's day. English kept Sunday and Saturday in their pre-Christian forms; French replaced them.

The lowercase rule

French does not capitalise days of the week. Mid-sentence, "lundi" is right and "Lundi" is wrong. The same rule covers:

Months: janvier, février, mars, avril, mai, juin, juillet, août, septembre, octobre, novembre, décembre.
Language names: anglais, français, espagnol, allemand, italien, mandarin.
Nationalities used as adjectives: un livre français, une amie anglaise.

The only time a day gets capitalised is at the start of a sentence or in a title. Writing "le Lundi 3 mars" is wrong; the correct form is "le lundi 3 mars". This is the single most common spelling error English speakers make in written French, because the English habit of capitalising days is so deeply trained that it survives years of French study. The capital is the tell.

Nationalities behave slightly differently when they refer to a person rather than an adjective: un Français (a French person) is capitalised, un livre français (a French book) is not. Days never get this treatment. They stay lowercase always.

The lundi-first week

French calendars start with Monday. The week reads lundi, mardi, mercredi, jeudi, vendredi, samedi, dimanche, with the weekend (samedi + dimanche) grouped at the end. This is the ISO 8601 standard, the same convention used in Spanish, German, Italian and most of continental Europe.

The US convention of starting the week on Sunday is the outlier here, and it can catch you out when reading French diaries, school timetables or appointment calendars. The Monday column is the first column. The weekend is the last two. If you are scanning a French school timetable looking for Tuesday at the start, you will not find it.

Bare lundi vs le lundi

This is the distinction the textbook tends to underplay. The presence or absence of the definite article changes the meaning.

Lundi on its own refers to a specific Monday, usually the coming one or the most recent past one depending on tense:

Lundi je vais à Paris. - This Monday I am going to Paris.
Lundi j'ai vu Marie. - On Monday I saw Marie (last Monday).

Le lundi with the article refers to Mondays in general, the habitual sense:

Le lundi je vais à la piscine. - On Mondays I go to the pool.
Le lundi est mon jour préféré. - Monday is my favourite day.

This is the same conceptual distinction that Spanish makes with singular vs plural (el lunes for one Monday, los lunes for Mondays in general). French handles it differently: the article does the work. Same logic, different mechanism.

Plurals

French days take an s only when they are habitually plural and the sentence wants to make that explicit:

les lundis - the Mondays (plural noun)
tous les lundis - every Monday
les lundis et les jeudis - on Mondays and Thursdays

Both le lundi and les lundis work for the habitual sense. The plural form is slightly more emphatic about repetition; the singular with article is the more common default. Dimanche pluralises the same way: les dimanches, tous les dimanches.

Yesterday, today, tomorrow

The day-relative vocabulary is hier (yesterday), aujourd'hui (today) and demain (tomorrow). The standard pattern uses c'est, not il est:

Hier c'était lundi. - Yesterday was Monday.
Aujourd'hui c'est mardi. - Today is Tuesday.
Demain c'est mercredi. - Tomorrow is Wednesday.

The English instinct to translate "today is" as "il est" produces correct grammar but wrong idiom. C'est is the natural form here. The two-step variants avant-hier (the day before yesterday) and après-demain (the day after tomorrow) round out the cluster.

Last, next, this

To anchor a day relative to the current week:

lundi dernier - last Monday
lundi prochain - next Monday
ce lundi - this Monday

The pattern is day + adjective for past/future, and ce + day for the current-week version. Ce lundi can refer to the Monday just gone or the one coming up depending on context, which is why lundi dernier and lundi prochain are useful when you need to be unambiguous.

Mercredi: the day off

French primary schools historically had Wednesday off, or a half-day on Wednesday morning. The arrangement dates back to the nineteenth-century separation of church and state: the day was kept free of secular school so that families could send children to religious instruction without it conflicting with the timetable. Over time the day off became a fixture of French childhood, used for music lessons at the conservatoire, sport, scouting, judo and grandparent visits.

The 2013 rentrée scolaire reform restored Wednesday morning classes in most regions, partly to spread the school week more evenly and reduce Friday afternoon fatigue. The lessons came back; the culture did not move. Mercredi after-school activities still anchor the rhythm, conservatoires are still packed on Wednesday afternoons, and grandparent pickup at Wednesday lunchtime is still a normal arrangement in many families. For an English-speaking learner this means mercredi is the most culturally marked day of the French week, and worth knowing as more than just "Wednesday".

Vendredi soir: the weekend starts here

In the UK the weekend starts on Saturday morning. In France it starts on Friday evening, and the language tracks it. Vendredi soir is the cultural opening of the weekend, not a precursor to it. The standard pre-weekend plan question in a French office or staff room is:

On y va vendredi soir? - Are we going Friday evening?

The bars and restaurants fill from about 19:00 on Friday. Saturday lunchtime is comparatively quiet because the socialising already happened. Calibrating your French diary to vendredi soir as the headline night, rather than samedi soir, is a small adjustment that makes everything else sit right.

Le weekend (or le week-end with a hyphen, both forms are accepted) is the standard term. It is one of the more visible English borrowings in French, and the Académie française's preferred alternative la fin de semaine reads as Quebec usage or formal writing rather than everyday spoken French. Use le weekend in conversation.

Abbreviations

The two abbreviation systems you will see on French calendars and timetables:

Three-letter	Single-letter
lun.	L
mar.	M
mer.	M
jeu.	J
ven.	V
sam.	S
dim.	D

The single-letter system has the obvious problem that mardi and mercredi both start with M. Calendars rely on column position to disambiguate, and some publishers use Me. for mercredi or italicise one of the two Ms. The three-letter system is unambiguous and is the safer default in any context where the abbreviation is not in a fixed column.

Common phrases

A small bank of high-frequency expressions:

Quel jour sommes-nous? - What day is it?
On est quel jour? - More casual version of the same question.
Aujourd'hui c'est mardi. - Today is Tuesday.
Du lundi au vendredi - Monday to Friday.
En semaine - During the week (as opposed to the weekend).
Le weekend - The weekend.
Tous les jours - Every day.
Un jour sur deux - Every other day.

The du... au... construction is worth memorising; it is the standard way to express a range of days in opening hours, school timetables and work schedules.

Cross-references

The French pillar covers the wider adult-learner approach for French.
French vocabulary by CEFR covers the frequency-ordered word list these days sit inside.
How to say good morning in French covers the bonjour cluster that pairs with the day vocabulary in any greeting.
French grammar covers the article and agreement rules that decide between bare lundi and le lundi.

Days of the Week in French: Lundi to Dimanche and the Lowercase Trap