The explanations are very technical on his clouds work and maybe that's what the asker of the question wanted. Really the question seems to beg a simple answer.<p>Clouds don't have a well defined boundaries. They are very large and we are generally very far away. If you fly through clouds or walk/drive through them on a mountain top it's clear they're not defined at all. From far away it looks like that cloud is a ceiling and when you reach it there's a binary effect but it's not.<p>Same thing from viewing lakes or oceans from very high up. They can look like big static bodies.