I recently read, "Reason can't defend itself without resort to reason." Is this universally true?

  • 2
    Just as "Reason cannot be rejected without resort to reason" is, one should add.
    – Philip Klöcking
    Mar 24, 2016 at 9:15

2 Answers 2


Yes, the only method we have to check reasoning is reason itself.

The main work of Kant is named Critique of Pure Reason (CPR). One can read the title in both ways "Reason criticizes" and "reason is criticized". Hence it comes up to "reason is criticized by itself".

CPR determines the boundary of possible knowledge. Notably, it criticizes metaphysics when it goes beyond this boundary. But CPR also finds out the presuppositions of all knowledge. These presuppositions are due to the fact that our reasoning is bound to certain forms of intuition and to certain rational categories.

Kants draws a boundary between understanding and reason. But this distinction is not relevant for the present question.

  • But reason defending itself with reason implies some sort of recursive relationship, correct? So at what point does reason become universally true?
    – acs254
    Mar 24, 2016 at 16:37
  • @acs254 Truth is a property of propositions. I consider the proposition "Reason can only be defended by reason" a true proposition. If you want to make a difference between "true" and "universally true", I would refer to modal logic and interpret "universally true" as "necessary true", e.g., "true in all possible worlds". - But in any case, it is not common to say "reason itself is true" nor "reason itself is universally true".
    – Jo Wehler
    Mar 24, 2016 at 16:57
  • @acs254 Yes, there is a circularity, which I tried to illustrate by the title "Critique of Pure Reason" of Kant's work.
    – Jo Wehler
    Mar 24, 2016 at 17:02

Good logic is generally experienced as something that people feel, as the impression of psychological clarity. If an argument cannot come to draw this response from someone mentally, it generally does not become part of their repertoire of reasonable arguments.

Neuroscientist Antonio Damasio, in "Descartes Error" argues this is not merely an appearance. He traces a correlation of brain injuries that suppress emotional responses with the lack of the ability to apply logic in practice. If 'logical' is a feeling, loss of emotion would also remove logic, at least to the degree it extends beyond grammar. And just that seems to happen.

But that means your answer is 'no'. In the sense that clarity is experienced in an emotion that we share, which is rather specific and reliable in its evocations, and we build rules and habits of reason out of our experiences with that emotion, reason itself still does not consist in the emotion.

But simple reason 'defends itself' through appeal to that feeling. This is what happens in philosophy when we appeal to intuition, and reach agreement, which happens often. Such agreement does not arise from reason, but from its sources, which is built into human instinct.

Applying further reason can lead us to or away from the impression of clarity, and the judgement itself can be trained, but we are constantly referring back to that feeling, and it is the ultimate defense.

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