Thank you fivejedjon,
I get your point. Can v Could and Will v Would should be used to express the certainty of what we say and we can use them in a flexible manner. So I can say: "Things could change very quickly (Not very certain), but we will remain strong and become stronger than ever (Very certain)" or "You can spend your money on anything you want (Very certain), but your job security would not be as stable as 3 years ago (Not very certain)"
Am I correct?