In fact, the more educated we become, the more our beliefs come to us at second hand. A person who believes only those propositions for which he can provide full sensory or theoretical justification will know almost nothing about the world; that is, if he is not swiftly killed by his own ignorance. How do you know that falling from a great height is hazardous to your health? Unless you have witnessed someone die in this way, you have adopted this belief on the authority of others .31