Using The Everyday French Phrase "C'est-à-dire"

"C'est-à-dire" is a very commonly used phrase that translates to "that is", "that is to say" or "in other words". It's often used to clarify or explain something that has just been said.

It helps clarify a statement by providing additional information or a more precise explanation, or rephrase something in simpler terms.

"Il est allergique, c'est-à-dire qu'il ne peut pas manger de noix."

He's allergic, that is, he can't eat nuts.

"C'est un athlète, c'est-à-dire qu'il s'entraîne tous les jours."

He is an athlete, that is he trains every day.

Expressing a consequence

Sometimes, c'est-à-dire is used with a meaning of "which means" or "as a result":

"Je suis occupé demain, c'est-à-dire que je ne pourrai pas venir."

I am busy tomorrow, that means I won't be able to come.

Another way to say it would be:

"Je suis occupé demain, ce qui signifie / ce qui veut dire que je ne pourrai pas venir."

Justifying something

Sometimes, "C'est-à-dire" is also used to give excuses or explanations for an embarrassing situation or something you did wrong. In these cases, it can translate to "the thing is...":

"Pourquoi tu n'es pas venu à la fête hier soir ?"
"C'est-à-dire que je ne me sentais pas très bien..."

Why didn't you come to the party last night?"
The thing is, I wasn't feeling very well…

"Tu n'as pas répondu pas à mes messages !"
"C'est-à-dire que j'ai perdu mon téléphone…"

You haven't answered my messages!
The thing is, I lost my phone…

In these types of situations, you might also use "à vrai dire" (truth be told) as an alternative to "c'est-à-dire":

"A vrai dire, je ne me sentais pas très bien..."

Using it for "what do you mean?"

In spoken French, when you need a clarification or more information about what the other person just said, you can say "c'est-à-dire ?" :

"Ah oui? C'est-à-dire ?"

Oh really? What do you mean?

An alternative is "Comment ça ?" (how so?)

"Je ne pense pas que ça va marcher..."
"C'est-à-dire ? Exprime toi clairement!"

I don't think this is going to work out...
What do you mean? Speak clearly!

Using it for "I mean"

"C'est-à-dire" can also be used as an introductory phrase when someone is thinking aloud or trying to explain something. It serves to buy time or clarify their thoughts.

"Je crois que je vais prendre le train... c'est-à-dire, si j'y arrive."