Lies and deceits.

I had a conversation the other day with a young man - a former pupil - who seemed most anxious to learn how you know when governments are lying.
I resisted the temptation to say "Whenever a politician opens his mouth...."
My considered response was:
"Whenever you are told that you must believe something and all debate is suspended - you are close. When you are then shouted down for your own contrary belief - that is the time when you know!"