I've been struggling with this lesson for a while now and keep getting the answers wrong in tests.  I think I have it now but the additional research I've had to do suggests there are issues with this lesson. 

(1) The heading is a bit misleading, causing me to think for a long time that "if" made the phrase conditional,  whereas of course it's "would" that does that.  This caused me to think the phrase order was "Si [le conditionnel] (then) [L'imparfait]", whereas it's the opposite for most of the examples. The true order, I realise know, is "Si [l'imparfait] (then) [le conditionnel]", or "[le conditionnel], si [l'imparfait]".

(2) More importantly, the lesson does not mention that the tense of the "if" phrase can vary depending on the likelihood of the "result" phrase. This lesson is focused only on the unlikely outcome and does not discuss or even mention the likely or impossible outcomes as far as I can see.  Is there a reason for this?