Originally posted by whodey
You cannot prove that smoking caused a cancer.
Only because there is a lack of evidence. You equally can't prove I ate sausages yesterday. All relevant evidence is gone (or will be by the time you start the investigation).
But it is a proven fact that smoking causes cancer.
All you can do is show the correlation between smoking and cancer.
To a high enough degree that there is no doubt whatsoever that smoking causes cancer.
It is like saying that someone became ill because they did not wear their coat on a cold day. All you can do is show the correlation that not wearing warm cloths increases your chances of catching a cold. It well may be that someone simply sneezed in their face and caused them to become ill.
Without monitoring someone's health, and studying every cell, it is often impossible to know very much about all the factors involved in a disease they have. Even relatively well known diseases often have complications unique to a given person that are difficult to identify. But failure to monitor every atom in the universe does not equate to 'nothing can be proven'.
All you are doing is saying: 'here is an example of something so complex that we don't yet know all about it, or simply do not have the ability to gather all the evidence: therefore nothing can be proven'. Sorry, but the conclusion cannot be drawn from the examples given.
Some things cannot be proven (and in the examples given it is merely due to a lack of evidence collection). But some things can be proven beyond reasonable doubt.