It is commonly accepted that the lack of evidence for a particular proposition makes belief in said proposition irrational.

However, imagine the following proposition,

P: An object exists for which evidence can never be comprehended nor even acquired by humanity.

This seems a certainly reasonable proposition, and in fact, belief in this proposition seems to be completely rational. After all, the universe is vast and perhaps infinite, and due to said vastness, the probability that such a thing exists which we can never reach, and, even if we did, would never be able to grasp due to our limited intelligence and perception, seems, to me at least, rather high.

And yet, by its design, this object has no evidence.

So, is this an example of a proposition which has no evidence but which it is still rational to believe in, and hence the premise that "each belief in something which has no evidence is irrational" ... is false?

One may counter-argue that the knowledge that our intelligence and perception is limited, coupled with the vastness of the universe, is itself evidence that such an object must exist. However, now I feel we are moving the goalposts and changing our definition of the word "evidence" into something less tangible and moving into the territory of probability, and it is well-known that probability is ridiculously hard to define and almost always subjective. If that is how we then wish to play the game, then "I believe in God because the probability that all of this came of nothing is so low according to my subjective probability distribution" must be considered an acceptable piece of evidence, which I don't feel it is.

  • Wittgenstein spoke of certain beliefs that are so fundamental that we never seek evidence for them. Such beliefs have a more solid foundation than what evidence could provide. He said, "Moore does not know what he asserts he knows, but it stands fast for him, as also for me; regarding it as absolutely solid is part of our method of doubt and enquiry." Wittgenstein thought it was unnatural to speak of knowing such thing because their certainty is not subject to evidence, so it's more natural to say "God exists" rather than "I know God exist," as if evidence were necessary.
    – user3017
    Oct 2, 2017 at 18:55
  • 4
    The usual objection is that this proposition is not only unreasonable but plainly meaningless. Our understanding of concepts like "object" and "exists" is based on some sort of perception/interaction, at least indirect. So what can "object for which evidence can never be comprehended nor even acquired" possibly do other than string words together? Before one argues for or against such an "object" the hurdle to overcome is to explain how such a thing is not an empty phrase, what Kant called "transcendental illusion".
    – Conifold
    Oct 2, 2017 at 19:40
  • Of course, when Kant was speaking of transcendental illusion, he wasn't speaking of the foundational truths that make knowledge possible. He asserted that we have certainty of certain non-empirical things, without which we couldn't grasp any empirical evidence: "[W]e might easily show that such principles are the indispensable basis of the possibility of experience itself, and consequently prove their existence a priori."
    – user3017
    Oct 2, 2017 at 20:02
  • The conscience of man testifies, as a matter of certainty, to the existence of objective moral truth, and that, in turn, presupposes God's authority whose existence is naturally recognized by mankind in other ways as well. Man's failure to acknowledge such thing is due to sin and a refusal to become reconciled with God. Thus, the epistemological hurdle is overcome first by repentance and then by learning the details which God has revealed in His word.
    – user3017
    Oct 2, 2017 at 20:40
  • @PédeLeão The a priori principles ("transcendental subject") are not exactly things, and they lack content without sensible intuitions. I think this is where Kant limits reason to make room for the faith, there is no knowledge of God we can have, a priori or empirically, nor is moral truth a matter of certainty, nor is its relation to God if it was. But we must act, and practical reason demands those things regulatively. But it does not seem to me that OP has something like God in mind, and one can certainly argue that evidence of God's existence can be both acquired and comprehended.
    – Conifold
    Oct 2, 2017 at 23:41

4 Answers 4


Your question consists of two parts, 1) "What defines lack of evidence"?, and 2) "is it irrational to believe in something without evidence"?

In order to answer the first part, we must recognize that there are different amounts/types of "evidence" that result in different "degrees" of certainty. There is, 1 - no evidence, 2 - preponderance of the evidence, 3- beyond a reasonable doubt, and 4 - absolute certainty.

For some people, any degree other than 4, would constitute "lack of evidence" for others, only degree 1, would.

The answer to the second part then, depends on the mentality of the person providing the answer.
For a person that requires only degree 1, there are 3 additional degrees that "provide evidence," therefore it would not be irrational to believe in the item in question. whereas, for a person that requires degree 4, it would be irrational to believe in something supported by the lesser evidence provided by degrees 2 & 3.

  • I think the a component of irrationality comes when you believe something over a large number of equally likely alternatives without any particular evidence to support that. Believing in, say, a invisible pink unicorn in your garage is highly irrational partly because there's millions of other invisible pink animals it could equally likely be. Oct 12, 2017 at 17:43

Your proposition simply isn't an example of a proposition that has no evidence to support it. You gave supporting evidence for the proposition:

  1. The universe is large (known to be true)
  2. Human intelligence is limited. (known to be true)

From that, you derived that there exists something that we won't ever know anything about, and wouldn't understand if we did.

I personally don't think your conclusion follows from your premises and I reject your proposition, but it has supporting arguments and evidence to support those arguments.


P: An object exists for which evidence can never be comprehended nor even acquired by humanity.

The opposite is true it's unreasonable to rule out that such an object could exist given the vastness of the universe and the limitation of our capabilities, due to let's call it the lack of evidence to the contrary. However the failure to reject with certainty is not the same as a necessity to accept the hypothesis with certainty. So the best you can say is to argue there is a probability somewhere between 0 and x% that such a thing exists. But then you'd be precisely at your last statement.

Also if we have no way to perceive it's existence then how could we even tell it exists in the first place?

And obviously that's an analog to the question of whether or not god exists so there's probably tons of material there that you can try to fit on your proposition.


'Lack of evidence' is the absence of sufficient reason to believe in a proposition.

The trouble is, 'sufficient reason' is subjective.

For some, 'sufficient reason' is acquired via scientific evidence, but for others, 'sufficient reason' relies only upon one's pre-existing beliefs, or upon their experience, which may or may not be accurate.

So, when we ask the question, 'Is it irrational to believe in something without evidence?', we realise that no, it is not. Because there is nothing about rationale that necessarily be accurate. 'Rationality' describes merely a process of reasoning; reasoning which may be well-founded or ill-founded. I can believe that aliens exist according to the rationale that I believe I was abducted by them whilst I slept, but there is nothing to say that my rationale is reasonable or justified.

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