The man of science relies on his own knowledge and observation and judgment, and disregards testimony.

A man comes to you and tells you he is blind in one eye.

Do you accept his statement?
Not in the least.

You proceed to test his eyesight with some infernal apparatus of coloured glasses, and you find that he can see perfectly well with both eyes.

Then you decide that he is not blind in one eye; that is to say, you reject his testimony in favour of facts of your own ascertaining." "But surely that is the rational method of coming to a conclusion ?" "In science, no doubt.