I guess reason can't be used to justify itself.

This is something Presuppositional Apologists love to play mischief with.

So how do we justify anything based on reason when reason itself is questioned? I always feel anyone who questions not your reasoning but reason itself saws off the branch they are sitting on, but when you suggest this the response is "tu quoque".

I guess you have to say reason is justified empirically/inductively? The innate function of a healthy mind?, it yields results, more than unreason?

Where can I read more about this? I'm guessing this is a well known issue in Philosophy.


4 Answers 4


What you are asking is how reasoning is justified. This is part of a more general problem about epistemological justification, but applied specifically to reasoning and logic. Charles Dodgson (aka Lewis Carroll) published a paper called "What the Tortoise said to Achilles" to illustrate this problem. It shows that you cannot justify a simple logical rule like modus ponens using logic without circularity.

Broadly there are two classes of response, internalist and externalist. Internalists hold that justification must be internal to the cognitive agent. One form of this is a kind of psychologism in which what justifies reasoning is the fact that the agent perceives the reasoning as being intuitively obvious. Descartes appears to follow this route, in that he frequently speaks of "clear and distinct ideas". The problem is that all kinds of things seem intuitively obvious and subsequently turn out to be false. It seemed obvious to people for a long time that the postulates of euclidean geometry were indubitably true; it seems obvious at first that if the universe is unbounded it must be infinite; it seems obvious that if a system is determinate it must be predictable.

Externalists, by contrast, hold that reasoning is justified by reference to facts outside the cognitive agent. One form of this is reliabilism, which is roughly the idea that reasoning is justified by the fact that it works well in practice, or else we would have discarded it. This rather assumes that we are indeed good at reasoning, which is moot, given that we know humans are subject to all manner of cognitive biases and in particular are notoriously bad at reasoning with uncertain information. Another version is to say reasoning is justified as being a successful evolutionary adaptation, i.e. being able to reason more or less correctly is justified by its survival value. Again, this is problematic because our reasoning may be just a side effect of some primitive ability possessed by our pre-human ancestors that helped them to overcome the difficulties of surviving in Africa, but doesn't of itself provide us with any confidence that it is good for solving problems in higher mathematics.

There is some more general information about internalist vs. externalist conceptions of justification in the Stanford encyclopedia article.


You can deny the compelling nature of reason all you want, but it is like denying the compelling nature of hunger. As noted in my response to Can reason defend itself without resort to reason? Humans have a subjective feeling of clarity, and reason appeals to it.

What is to be gained by denying hunger? As much is to be gained by denying reason. Both of them are evolved responses that allow for survival in an environment.


If by reason, you mean logic, then a good place to start would be to teach logic in a simplified form to the layperson which should be easy because the nature of logic is to be intuitive.

Otherwise rejecting the unknown is just human nature.


An apologetic pastor at my church once pointed out that we have three epistemological "tools" two of which many "logicians" may consider to be unlogical or unreasonable. These three are:

  1. Reason - the very thing being questioned by the OP
  2. Experience (relates to measurement and testing, experience of the physical world)
  3. Faith (not referring to religion, but trust)

Reason is "obvious", as people pointed out, it is the deductive process by which we gain clarity on a subject.

Through experience we might make some inferences about the "reality" we perceive. Given consistent experiences from various agents in various situations, through reason we may assemble a picture of reality, or at least the reality of the sample space and test subjects.

One thing we tend to take for granted in our everyday reasoning endeavours and tend to overlook when we try to answer questions such as the one posed by the OP is faith, or trust.

Ultimately, when you come to a logical conclusion and are sure you know the answer you unwittingly, and maybe reluctantly, place faith in the correctness of your reasoning and consistency of your experience.

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