Si is a little French word that mainly corresponds to three little English words: "if," "so," and "yes." Although these are three very different words, it’s usually easy to tell which one si is referring to in context. So let’s see what si can do!
Most of the time, you’ll probably hear si used to mean "if," as Bertrand Pierre uses it in his emotional song Si vous n’avez rien à me dire (with text by Victor Hugo, of Les Misérables fame):
Si vous n'avez rien à me dire / Pourquoi venir auprès de moi?
If you have nothing to say to me / Why come up to me?
Captions 1-2, Bertrand Pierre: Si vous n'avez rien à me dire
Note that when si meaning "if" is followed by il ("he" or "it") or ils ("they," masculine), it is contracted to s'. This is perhaps most commonly seen in the expression for "please," s’il vous plaît (formal) or s’il te plaît (informal), which literally translates to "if it pleases you."
Si can also be used to indicate a contrast or opposition, in which case it means "whereas":
Si Émilie aime la musique rock, Henri la déteste.
Whereas Émilie loves rock music, Henri hates it.
Since si and "so" look quite similar, it shouldn’t be too hard to remember this meaning of the word. Just keep in mind that si refers to the adverb "so" (as in "so happy"), not to "so" as a conjunction (as in "move so I can see"):
Pourquoi si long et pourquoi si las, tenir à bout de bras?
Why so long and why so weary, to hold at arm's length?
Caption 26, Dahlia: Contre courant
One of the first words you learn in French is the word for "yes," oui, but sometimes si can also mean "yes" (as it does in Spanish and Italian). However, si only means "yes" in a very specific context: when someone is contradicting a negative question or statement. In case that sounds kind of convoluted, here's an example:
Non! Il n'est pas bien, Sarkozy! -Si, si, si. -Si, il est bien.
No! He's not good, Sarkozy! -Yes, yes, yes. -Yes, he's good.
Captions 15-17, Interviews à Central Park: Discussion politique
If oui were used here instead of si, the speaker would just be confirming the negative statement ("Yes, Sarkozy is not good"). On the other hand, si takes a negative proposition ("He's not good, Sarkozy!") and turns it into a positive one ("Yes, he's good"). This is why it can come in very handy when you want to correct someone or express a contrary opinion.
To conclude, here are two expressions with si that you might find useful: si ça se trouve... ("maybe" or "it could be the case that") and si ce n'est que... (apart from the fact that):
Si ça se trouve, Georges n'a jamais terminé ses études.
It could be that Georges never finished school.
Nous n'avons rien en commun, si ce n'est que nous sommes tous les deux français.
We have nothing in common apart from the fact that we are both French.
This tiny word is probably one of the most versatile in the French language. So now that you know all about si, here's a challenge for you: try writing a two-sentence dialogue using as many meanings of the word as you can. Just use this lesson as a guide, and it'll be easier than you think!