Si meaning whether, and si or quand

Si meaning whether

When si asks an indirect question, it means whether, and the golden rule does not apply. The future and the conditional are both fine after it:

• Je ne sais pas si elle viendra. - I don't know whether she will come.
• Il m'a demandé si je viendrais. - He asked me whether I would come.
• Je me demande si nous aurons le temps. - I wonder whether we will have time.

The test: swap if for whether in the English. If the meaning survives, it is the whether-si, and the tense is free.

Si or quand?

English puts a present after both if and when. French does it only after si. After quand, a future event takes the future:

The glosses: If you come, we will go to the cinema. When you come, we will go to the cinema.

Mistakes English speakers make

The last row is about a future visit, where careful French wants the future; quand tu viens is right for a habit (whenever you come), and in casual speech you will also hear it for a plan.