It is irrational to believe anything on insufficient (or the lack) evidence?

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Do we need to have a sufficient evidence in order to believe something to be the case? Is it irrational to believe anything on insufficient evidence? Philosopher W. K. Clifford (1845-1879) argued it to be case, and called it the ethics of belief. “It is wrong always, everywhere and for anyone, to believe anything upon insufficient evidence” (Clifford 1879).

The sincerity of the believer towards his conviction is of no help. He is not justified in his beliefs because he wants “to believe them, and because they are comforting and pleasant.” Rather it is his duty to question and doubt his beliefs. For it is irrational to suppress ones doubts while at the same time avoiding the investigation. Although Clifford understood that that duty is a hard one, still, to avoid credulity, one has to embrace it (Clifford 1879).

If a man, holding a belief which he was taught in childhood or persuaded of afterwards, keeps down and pushes away any doubts which arise about it in his mind, purposely avoids the reading of books and the company of men that call in question or discuss it, and regards as impious those questions which cannot easily be asked without disturbing it—the life of that man is one long sin against mankind (Clifford 1879).

Clifford’s concern, however, is not ontological, but rather epistemological. Are we justified in holding a particular belief, for example, the virgin birth or the resurrection of Jesus? In short, he is concerned more about how we know such beliefs, and whether we are justified in holding so.

The question of right or wrong has to do with the origin of his belief, not the matter of it; not what it was, but how he got it; not whether it turned out to be true or false, but whether he had a right to believe on such evidence as was before him (Clifford 1879).

The event, say the virgin birth or the resurrection of Jesus could be true, but the issue Clifford concerned himself with, is whether we are justified in believing that such events really took place.

The thesis of Clifford came as a counter-argument against Pascal’s Wager. Blaise Pascal (1623-1662) proposed a pragmatic justification for the religious belief in God, concluding that it is reasonable for one to believe in God in light of the evidence or the lack thereof.


Was Clifford right in saying so? Is it really irrational and sinful against mankind to believe anything on insufficient evidence? Let us reflect its strengths and weaknesses.


  • Having sufficient evidences for believing what you believe, and doubting what you doubt, is a virtue. It is a mark of a reasonable man. Credulity, on the other hand, is a vice. It usually rest on believing something because it is attractive, comfortable, pleasant or beneficial to do so.
  • Addressing doubts and doing the investigation may raise your confidence, if not the justification, of your belief. In short, it can make your beliefs stronger.


  • Sufficiency is person-relative. Person A can believe it is sufficient for him to just scan his notes, take the exams and pass it, while Person B believes that that kind of preparation is insufficient.
  • Experience tells us that its not credulity to hold onto something we have no sufficient evidences for. For we do it all the time. To give three examples,

    a) In pursuing a woman to marry, the man does not need to have sufficient evidences for his win to do the courtship, he must be prepared to be rejected also.

    b) In using abstract objects like numbers (1-n) or relational terms (e.g., greater than), we never paused for a while to think whether we have sufficient evidences to use those entities. No, we just use them right away, and we’re not irrational to do so.

    c) In doing a scientific research, the researcher does not need to know and have the sufficient evidences for every particular case (for it is not in his reach to have so), or else his can’t finish his research. In short, he must trust the testimony of the the people who did the experiments (assuming that they’re being honest).

  • It paralyzes judgements. For we need to have sufficient evidences and be aware of it in everything we believe and do. For instance, before you can believe that you can brush your teeth, you need to have and be aware of the evidences: that you have a toothbrush, that your toothbrush is available for usage, that you still have a toothpaste, that you can go towards the sink without loosing vitality, and so on.
  • Lastly, Clifford, also, didn’t have the sufficient evidences for holding such belief, and prescribing such a duty. In short, his thesis undermines his thesis.


The evaluation, however, is still subject revision. Things might be added and omitted. Nevertheless, from the above reflections, we can deduce that it’s not irrational to believe anything on insufficient (or the lack) of evidence. Unless of course, there’s an evidence for the otherwise. But that’s another story.

W. K. Clifford, Lecturers and Essays (London: Macmillan, 1879).


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