Your Challenge - Be Skeptical

Having declared my interest, I am now going to summarize the arguments and challenge you to make up your own mind on the matter. I hope you will read what follows with skepticism. In particular, you should be wry of believing that just because something follows something else, the second must necessarily be a consequence of the first. Let me give you an example of what I mean.

I used to suffer wretchedly from repeated colds, often every two or three weeks. Years ago, I started to take 1,000 mg of vitamin C every day and, whenever a cold seemed to be threatening, I increased the dosage to 2,000 or 3,000 mg daily. Since then I have hardly even had an established cold and, almost always, find that I can abort a threatened cold with the extra dosage.

This is not proof. On this basis alone, I am not entitled to believe that it is the vitamin C that is preventing the colds. Other things may have happened, coincidentally with my starting to take the vitamin, that increased my resistance to colds. When I became a full time writer I changed my lifestyle and cam in contact with far fewer people. This could have been the cause. It is even possible that my expectation of benefit from vitamin C brings this about by some obscure psychological effect on my immune system.

But if, at the same time, I have evidence that the viruses that cause colds do their cellular damage by producing free radicals ( I don't actually know this, but it could be true), and that vitamin C can mop up free radicals, then I am entitled to have more confidence in the idea that vitamin C prevents colds. Since I have no evidence that viruses produce free radicals, I must continue to consider the matter 'not proven'. The Romans recognized the logical fallacy of believing that because one even follows another the former must have been the cause of the latter. They called it the post hoc ergo propter hoc fallacy ( 'after this, therefore because of this'). This is one of the commonest forms of logical error, and we are all prone to it.
 
Te many important facts presented to you in this book have been scattered between the chapters. It seems useful, therefore, to bring them all together in a brief summary, expressed in a slightly different way, so that you can pick up any points you have missed.