In his 1877 essay The Ethics of Belief, William Clifford argues that humans have a responsibility to inquire about the truth of their beliefs, not believe anything without sufficient proof, and consider the importance of their beliefs in possibly harming others. He says "It is wrong always, everywhere, and for anyone, to believe anything on insufficient evidence."
He gives the example of a ship owner who did not properly inspect a ship for safety, and believed the ship was seaworthy on insufficient evidence. The ship ends up sinking and harming many.
One aim of Clifford's essay is the superstitious beliefs held by many with no evidence, and usually with evidence to the contrary. He would include in this belief in God.
We can consider two parts of Clifford's essay. One is the responsibility of humans to have evidence or justification for their beliefs. The other is the particular kind of evidence that Clifford was thinking is sufficient.
Responsibility includes the community and the individual. A person who does not take care in forming beliefs harms the self and is a potential harm to others (as in the example of the ship). Clifford analyzes beliefs in terms of the potential for harm. I'd like to suggest there is another dimension he did not consider, which is the role of the belief within a person's worldview. Those beliefs that are assumed as basic by the rest of the worldview have the important role of holding the worldview together. Since their truth is assumed, if in fact they are not true then this has implications throughout the system.
Since the basic beliefs of a worldview involve questions about the highest authority, what is real, and what is of highest value, mistakes about these will impact how the individual interprets his experiences, and create divisions between persons as their interpretations clash.
Clifford's idea of evidence needs to be analyzed. It is one thing to give evidence about the safety of a ship. How does one give evidence to answer the question "what is the highest authority?"? The word "evidence" seems to indicate some kind of physical and empirical proof, such as "there are holes in the ship." Many have taken this kind of evidence as needed to prove religious claims, and appeal to miracles, or an empty tomb, to support their beliefs. The problem with this kind of evidence is that it must be interpreted, in each case we can ask "what does that mean?"
Giving evidence for basic beliefs is different than giving evidence that a ship is seaworthy. Persons have already limited the kinds of evidence they consider when they answers the question "what is the highest authority." At this level, what we're looking for is the meaning of a belief. Some common examples of "highest authorities" are: the senses, an inner religious experience, tradition, scripture/testimony of others. In each case a final appeal to such a source leaves questions unanswered. Why that tradition, why that testimony, how do we interpret that inner experience?
And so while Clifford seems to make some important insights, we are left without any answers as to how we get sufficient evidence for our most basic and important beliefs. In my earlier post on Externalism I suggested that questioning stops with reason because reason makes questioning possible. What we can do is apply reason, for instance the law of non-contradiction, to Clifford's own basic beliefs, such as "only the material world exists, and the material world is eternal." It is this kind of self-examination that Clifford should have done if he took seriously his own charge to inquire about the sufficiency of our beliefs.