For a theory of nescience, in condemning all knowledge and the faculty of knowledge, condemns itself.  If nothing is true, or if nothing is known, then this theory itself is not true, or its truth cannot be known.  And if this theory is true, then nothing is true; for this theory, like all others, is the product of a defective intelligence.  In whatsoever way the matter is put, there is left no standing-ground for the human critic who condemns human thought.  And he cannot well pretend to a footing in a sphere above man’s, or below it.  There is thus one presupposition which every one must make, if he is to propound any doctrine whatsoever, even if that doctrine be that no doctrine can be valid; it is the presupposition that knowledge is possible, and that truth can be known.  And this presupposition fills, for modern philosophy, the place of the Cogito ergo sum of Descartes.  It is the starting-point and criterion of all knowledge.

It is, at first sight, a somewhat difficult task to account for the fact, that so keen an intellect as the poet’s did not perceive the conclusion to which his theory of knowledge so directly and necessarily leads.  It is probable, however, that he never critically examined it, but simply accepted it as equivalent to the common doctrine of the relativity of knowledge, which, in some form or other, all the schools of philosophy adopt.  But the main reason will be found to lie in the fact that knowledge was not, to Browning, its own criterion or end.  The primary fact of his philosophy is that human life is a moral process.  His interest in the evolution of character was his deepest interest, as he informs us; he was an ethical teacher rather than a metaphysician.  He is ever willing to asperse man’s intelligence.  But that man is a moral agent he will in no wise doubt.  This is his

            “Solid standing-place amid
  The wash and welter, whence all doubts are bid
  Back to the ledge they break against in foam."[A]

[Footnote A:  Francis Furini.]

His practical maxim was

“Wholly distrust thy knowledge, then, and trust
As wholly love allied to ignorance! 
There lies thy truth and safety."[B]

[Footnote B:  A Pillar of Sebzevar.]

All phenomena must, in some way or other, be reconciled by the poet with the fundamental and indubitable fact of the progressive moral life of man.  For the fundamental presupposition which a man makes, is necessarily his criterion of knowledge, and it determines the truth or illusoriness of all other opinions whatsoever.

Now, Browning held, not only that no certain knowledge is attainable by man, but also that such certainty is incompatible with moral life.  Absolute knowledge would, he contends, lift man above the need and the possibility of making the moral choice, which is our supreme business on earth.  Man can be good or evil, only on condition of being in absolute uncertainty regarding the true meaning of the facts of nature and the phenomena of life.