He assumes as axiomatic certainties and insoluble mysteries the existence of the spiritual life in man, the union of the human and divine, and the freedom of the spiritual personalities, though in a sense dependent upon the Universal Spiritual Life.

This of course does not mean that he is in the habit of making unjustifiable assumptions.

This is far from being the case; on the contrary, he takes the greatest care in the matter of his speculative bases.

There are some fundamental facts of life, however, which according to Eucken are proved to us by life itself; we feel they must be true, but they are not truths that can be reasoned about, nor proved by the intellect alone.

These are the three great facts mentioned above, which, while not admitting of proof, must be regarded as certainties.
His contention that they cannot be reasoned about has led to the further charge of irrationalism.