Romansh: Our observations might be considered facts ... but there is always uncertainty with observations. > > At work people talk about processes that have been proven, ie used successfully for a century or so. What they mean they have been demonstrated. The next ore we find or concentrate we buy might not be amenable to the process.-You have been quite clear about your viewpoint. Thank you. I'm sure you accept simple causation: i.e., I throw the switch and the light comes on.