The Principle of Reason [28-29]

of reason makes the greatest claim to a foundation. The reason for the principle of reason would then be the most eminent of all reasons, something like the reason of reasons.

But what are we getting ourselves into if we take the principle of reason at its word and move towards the reason of reasons? Does not the reason of reasons press forward beyond itself to the reason of reason of reasons? If we persist in this sort of questioning, where can we find a respite and a perspective on reason? If thinking takes this path to reason, then surely it can't help but fall intractably into groundlessness.[8]

So one might like to make a cautionary note here: whoever takes such a path to reason is one whose thinking runs the danger of going to ruin. This warning may harbor a deep truth. But it may also be just a pathetic defense against the claim of thinking. In either case we see that there is something special about the principle of reason and its foundation, the principle as a fundamental principle. According to one view, we understand the principle without further ado and, without scrutiny, lend credence to it. According to the other view, the principle seems to thrust our thinking into groundlessness as soon as we take what the principle says seriously in relation to the principle itself.

Thus the principle of reason casts an odd light on the path to reason and also shows us that if we meddle with fundamental principles and Principles, we reach a remarkably ambiguously lit, not to mention perilous, province.

This province is familiar to many thinkers, even though they justifiably seldom speak of it. To know a little about a few of them might be of some help to us, who stand at the beginning of the path to the fundamental principle of reason and are strangers in this province. In discussing the principle of reason we are on guard as much against hasty and inflated claims as against a thought-weary modesty.

It is well known that Descartes wanted to bring all human knowing to an unshakable ground (fundamentum inconcussum) by first doubting everything and acknowledging only what presented itself clearly and distinctly as secure knowledge. Leibniz remarked that Descartes' procedure neglected to specify what was entailed in the clarity and distinctness of cognition that count as his leading principles. According to Leibniz, Descanes had at this point doubted too little. Concerning this, Leibniz said in a letter to Johann Bernoulli on August 23, 1696: sed ille dupliciter peccavit, nimis dubitando et nimis facile a dubitatione discedendo; "but he (Descartes) failed in a two-fold manner, by his doubting too much and by too easily desisting from doubting."4

What do we learn from these words of Leibniz? Two things are needed simultaneously for the path to reason and for residing in the province of fundamental principles and Principles: cleverness of thinking and reticence-but both always at the right place.

Therefore, in the fourth chapter of the fourth book of the Metaphysics, where

The Principle of Reason (GA 10) by Martin Heidegger