All rational thinkers would clearly know that in a series of arguments anything that appeals to faith would be considered a fallacy.

Yet the rational process itself (the belief that arguments based on sound logic would lead to the correct answer) is itself a belief based on acceptance based on assumption or because it has happened till now.

So does one question the rational process?

  • You mention "appeal to faith" and then the "belief based on acceptance [?] based on assumption or because it has happened till now". Are you implying that the latter is also faith? Have you considered you might be equivocating faith = belief?
    – DBK
    Commented May 25, 2014 at 6:35
  • (1) The 'rational process', whatever it may be, is not a belief. (2) Arguments based on sound logic lead to 'the correct answer' by definition; there is no faith involved. (Once you understand the classical definition of logical consequence and then look up the definition of what makes an argument sound, you'll come to see that fact. The key notion is truth (not faith) preservation.) Commented May 25, 2014 at 6:55
  • @HunanRostomyan: Doesn't the acceptance of a definition too necessiate some amount of belief in the definition itself? Commented May 25, 2014 at 7:28
  • @user3660112 What exactly would the content of such a belief be? (Nothing you believe about the definition can make any theoretical difference to what you can do with the definition. You can think it's a useful definition, you can think it's particularly neat, and so on. But, none of those (or any other) attitudes is necessitated by your acceptance of the definition.) Commented May 25, 2014 at 7:42
  • 1
    Yes, one does question everything!
    – Asphir Dom
    Commented May 28, 2014 at 18:38

3 Answers 3


The question reminds of the problem with Cartesian doubt and of the Clifford-James debates (somewhat poorly named because Descartes is not actually subject to this type of doubt).

Early in the Meditations, Descartes looks at the consequences for a species of radical skepticism. Here, he looks at the most radical denial of our ability to trust our faculties of reason suggesting that we cannot even trust our ability to reason about our faculties of reason. The problem is that if we reach such a state of non-trust, we also cannot trust our doubts. How does Descartes escape? Well, you should really read the Meditations but briefly he suggests that there's a God who is not an evil demon and isn't manipulating our thought process to the point where we cannot rely on it, and that we have in our thoughts "clear and distinct" ideas which have a special difference from all of our other ideas.

The Clifford-James debate revolves around a claim by W.K. Clifford that we should only believe what we have sufficient evidence to believe. But the problem is that this turns out to be a criterion for which the rule (or whatever level of rule prime) will not be able to pass muster. Williams James is deeply critical of this and suggests that we are all using "faith". But here we need to remember James is a type of pragmatist.

Most rational accounts are going to end up pulling something similar to Descartes -- we are going to need some minimal set of faculties that just plain work to get to any truth. Hume as a type of empiricist and skeptic thoroughly agrees but denies we have such faculties. Kant, on the other hand, thinks that these faculties are implicit in knowledge claims and not problematic insofar as what we say about objects reflects not on the things-themselves but the things as rendered to us through our faculties of understanding and perception (which impose 12 categories and forms of sensibility [space and time] respectively).

Now I take i what Hunan is arguing with you about in the comments is that "belief" and "faith" can have a very wide array of meanings, and it's not clear if you mean what I've answered above or if you mean something else that equates this with what we might call "religious belief" or fideism. There things will get a lot dicier and you're going to have to make a much more robust argument if you want to claim that believing we can trust our sense and our faculties is the same sort of thing as believing in God.


Rationality does not consist in the idea that our ideas should be "based on sound logic". Every argument makes assumptions, including assumptions about the right rules of inference. Those assumptions are not proven because in order to prove them you would need a further argument that would make more assumptions that have to be proven and so on, leading to an infinite regress. Rather, we create knowledge be noticing problems, making guesses about solutions to those problems, criticising the proposals until only one is left and then looking for problems with our new ideas. Rationality consists in being willing to discard any idea that does not survive criticism. See "Realism and the Aim of Science" by Karl Popper, Chapter I.

Some philosophers have tried to criticise this idea by saying things like "you shouldn't throw out an idea as soon as there is a criticism of it." But if you see a criticism and you correctly think you know how to answer it, then when you have answered it your original idea has an addition that takes account of the criticism.

Other philosophers have stated that unless you have justified an idea you can't rely on it to solve practical problems. Since these people are advocating using an idea has not survived criticism they are criticising the standard of rationality described above. The way you should decide on a practical problem is to make suggestions for how to solve it and then criticise them. If your idea clashes with some other idea that has survived criticism that is a criticism of your proposal. If an idea that people wrongly think of as justified criticism then you should take account of it when making practical decisions when it is relevant, otherwise you should not take account of it.

You can criticise rationality, just not successfully.

  • You assume obviously that the number of ideas (in each practical example for the rationality to be used) is finite - > this type of rationality is practiced by every human in the universe and even animals. It is called trial and error. He talks about the cases when rationality (and spirits carried away by it) try to span this simple method on problems which have infinite number of supporting and opposing ideas.
    – Asphir Dom
    Commented May 28, 2014 at 18:36
  • There is no controversy in which infinite numbers of ideas have been proposed since there we don't control enough information storage capacity to store infinite numbers of ideas.
    – alanf
    Commented May 29, 2014 at 13:02

A very nice articulation of basically this problem is from C.S. Lewis in What the Tortoise said to Achilles.

As a short summary, the Tortoise presents the following to Achilles:

A: "Things that are equal to the same are equal to each other"

B: "The two sides of this triangle are things that are equal to the same"

Therefore Z: "The two sides of this triangle are equal to each other"

This seems like an obvious syllogism, and Achilles agrees, but the Tortoise points out that one could argue for the necessity of accepting:

C: "If A and B are true, Z must be true."

Which is essentially the base of the logic being used. But even if one accepts this, one must then accept:

D: "If A, B, and C are true, Z must be true."

And so on. The point is that one can continue this forever, and even with all these assumed premises one needn't accept the conclusion. Ultimately, as you say in your question, it comes down to a matter of giving up on all the technical premises and just saying "Z must be true because of the above" regardless of the hidden assumptions beneath that.

  • It is by Lewis Carroll, not C.S. Lewis.
    – E...
    Commented Mar 14, 2016 at 23:01
  • @EliranH maybe they were really the same person...
    – user16869
    Commented Mar 15, 2016 at 2:44

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