Therefore, So, Thus and Hence in French

Cause and consequence is the easy half of the French connector system: no subjunctive anywhere, no traps of mood. What it does have is a register ladder and a couple of positional rules, and choosing the wrong rung is what makes a sentence sound like a phrasebook. Here is the family, from the word you will use every day to the ones that belong in print.

So and therefore: donc

Donc is the workhorse, and the most famous word of French philosophy:

• Je pense, donc je suis. (I think, therefore I am.)
• Il pleut, donc nous restons à la maison. (It is raining, so we are staying home.)

Donc is unusually mobile. It joins clauses (il pleut, donc je reste), opens a sentence (Donc, tu viens? - so, are you coming?), and slips in after the verb (nous restons donc ici). That last slot, verb-then-donc, is the elegant one in writing: le projet a donc été annulé (the project was therefore cancelled).

In speech, donc also does the job of picking up a dropped thread: donc, comme je disais... (so, as I was saying).

So, spoken: alors

Alors is donc's conversational cousin. It means so in the sense of in that case or what happened next, and it runs half of French small talk:

• Il était fatigué, alors il est parti tôt. (He was tired, so he left early.)
• Alors, on fait quoi? (So, what do we do?)

The difference: donc draws a conclusion; alors moves the story on. In careful writing, a reasoned consequence wants donc or the formal set below; alors in an essay reads like chat. You will also hear du coup doing the same job in casual speech (du coup, on est partis - so we left); it is very common, very informal, and best kept out of anything with a header.

Therefore, formal: par conséquent, en conséquence, c'est pourquoi

When the register climbs, French swaps in the long forms:

• Le budget est limité; par conséquent, il faut choisir. (The budget is limited; therefore, we must choose.)
• La demande a baissé; en conséquence, la production ralentit. (Demand has fallen; consequently, production is slowing.)

Par conséquent and en conséquence are the therefore of reports, essays and official prose - the register where English would also write consequently. Like their English cousins they are adverbs: full stop or semicolon before, comma after.

C'est pourquoi (that is why) sits in the middle of the ladder and is the natural narrative connector:

• Elle a beaucoup travaillé; c'est pourquoi elle a réussi. (She worked hard; that is why she succeeded.)

Thus in French: ainsi

Ainsi is thus, and it is a written word - in speech, donc covers it. Mid-sentence it is straightforward:

• Elle a ainsi gagné sa place. (She thus earned her place.)

At the head of a sentence in formal prose, ainsi triggers a small inversion of subject and verb, and this is the detail worth learning because it is a hallmark of educated written French:

• Ainsi a-t-il décidé de partir. (Thus he decided to leave.)
• Ainsi s'explique son silence. (Thus his silence is explained.)

Without the inversion, sentence-initial ainsi shifts towards in this way: Ainsi, vous pouvez payer en ligne (this way, you can pay online). Both are correct; the inversion signals the logical thus.

Hence in French: d'où

D'où is hence, and it obeys one strict rule: a noun follows, never a clause.

• Il a menti, d'où le problème. (He lied, hence the problem.)
• Personne ne l'avait prévenu, d'où son étonnement. (Nobody had warned him, hence his surprise.)

To attach a full clause, rebuild with c'est pourquoi (il a menti; c'est pourquoi personne ne le croit) or the literary de là vient que. And keep the day job in mind: d'où still means from where in questions (D'où viens-tu? - where are you from?), so the comma in front is what tells you it means hence.

Because, four ways: parce que, car, puisque, comme

The reverse direction - attaching the cause - has four words that English flattens into because, and they differ by position and by what the listener already knows:

• parce que - the neutral because, and the only one that can answer pourquoi? on its own. Je ne sors pas parce qu'il pleut. (I am not going out because it is raining.)
• car - for. A written coordinator: it cannot open the sentence and cannot answer a question. Il ne viendra pas, car il est malade. (He will not come, for he is ill.)
• puisque - since, for a reason the listener already accepts. Puisque tu es là, aide-moi. (Since you are here, help me.)
• comme - as, and it must go first, stating the cause before the result: Comme il pleuvait, nous sommes restés. (As it was raining, we stayed in.)

That last rule is the mirror of Spanish como and catches the same learners: nous sommes restés comme il pleuvait does not mean because - moved to the back, comme slides towards as/like.

Grâce à (thanks to) marks a positive cause and à cause de (because of) a neutral-to-negative one, both with nouns: j'ai réussi grâce à toi (I passed thanks to you); le vol est annulé à cause de la neige (the flight is cancelled because of the snow). Swapping them is a classic slip - grâce à la tempête congratulates the storm.

The connectors at a glance

Common mistakes English speakers make

D'où + clause. D'où il est parti for hence he left is wrong: d'où takes a noun. Rebuild with c'est pourquoi.

Car at the front. Car cannot open a sentence or answer pourquoi. If in doubt, parce que is always safe.

Comme at the back. Comme only means because when it leads. Cause second means parce que.

Alors in formal writing. It is not wrong, it is just chatty. A report wants donc or par conséquent.

Grâce à for bad news. Grâce à congratulates its cause. Storms, delays and illnesses take à cause de.

See also

• Connectors of contrast and concession - however, although, even though and despite: cependant, bien que, même si and malgré.
• si clauses - condition, the other way of linking cause to outcome.
• Word order - where adverbs like donc and ainsi actually sit in the sentence.
• The French grammar cheatsheet - the whole grammar map at a glance.