A scientist and a logician had met Nasrudin and wrangled with him
as they walked along a road. Nasrudin was hard-pressed. The scientist 
said: ‘I cannot accept anything unless I carry out a test, or unless I see
it with my own eyes.’ The logician said: ‘I cannot attempt anything 
unless I have worked it out in theory beforehand.’
   Suddenly Nasrudin knelt down and started to pour something into a
lake beside the road.
   ‘What are you doing?’ they asked together.
   ‘You know how yogurt multiplies when you put it into milk? Well, I 
am adding a little yogurt to this water.’
‘But you can’t make yogurt that way!’
   ‘I know, I know…but - just supposing it takes!’