Hey, thank you for your comment. Sometimes there are no written rules when it comes to Swedish. I would believe that you need to learn the word order by heart. It takes a lot of listening and reading but it will become more natural the more advanced speaker you are. … It simply doesn’t sounds quite right to say “Ifall du inte kan komma du måste ringa”. Note that we say du måste ringa but if we yous a conditional clause we change the word order. Hope it helps a bit :-)