The first two are:
1.When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2.The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
Arthur C. Clarke, the famed sci-fi author who penned these laws, is probably best known for co-authoring the screenplay to 2001: A Space Odyssee
The third law has a nice ring to it, but it has extremely deep implications when you’re writing science fiction, or fantasy that has magic. Thinking about the law is very useful to keep your technology technology (and not basically magic that happens to run on electricity) and magic magic (and not technilogy that happens to run on plot holes).