In Life’s Basis and Life’s Ideal he analyses the various systems of thought which have been presented to the world.  He finds many of these deficient; but although something that is contained in them has to pass away, they possess some spiritual element which requires preservation, and which is valid for all time.  None of these systems is final; they have to preserve what is spiritual within them, and also merge it in some newer revelation gained for mankind.  Every system of the universe and of life has to move; it has perpetually to drop something of its accidentals, and continually strengthen and increase its essentials.  Everywhere emphasis is laid on the fact that the spiritual element [p.240] must be preserved and increased at whatever cost, for it is an element of the highest value for the world, and constitutes the energy of the world’s upward march.

In the Einheit des Geisteslebens, as well as in the Prolegomena to this, the necessity of a spiritual conception of knowledge comes to the foreground.  All systems of Naturalism lack enough spiritual life within themselves to meet the deepest needs of the race.  Man is more than all such systems.  Even on the grounds of the Theory of Knowledge itself man can be proved to be more.  Eucken deals in these two books with the content of consciousness:  that content reveals what is a Whole or Totality, what is beyond sense, what includes within itself the isolated impressions of the senses or of the understanding, and what is therefore spiritual in its nature.

In the Kampf um einen geistigen Lebensinhalt—­a book of the greatest value—­we find Eucken at his best.  His attempt here is to deal with the struggle for the spiritual life and the certainty of its possession.  He shows how man has emerged out of Nature, and how he has moved in the direction of gaining an inner world during the long course of civilisation, culture, morality, and religion.  Through titanic struggles this inner world becomes man’s possession, and constitutes the true value and significance of his life.  Man now realises that it is this world of spirit and values [p.241] which constitutes the only really true world.  Issuing out of this possession of the ever richer contents of this inward, spiritual world, the personality constantly becomes something quite other than it was, and its possession adds to the inheritance of the spiritual ideals of the world.  At this source man is in possession of a power of a new kind of creativeness in any field of knowledge or life he may be obliged to work.  Nothing blossoms or bears fruit without the presence and the power of spiritual life in the deepest inwardness of the soul.

In The Truth of Religion Eucken roams in a vast territory.  All the oppositions of the ages to religion are brought on the stage, and are made to reveal their best and their worst.  He shows how every system of thought, devoid of the experience and activity of the deepest soul, fails to engender religion.  He shows over against all this the intellectual warrant for religion, and passes from this to the personal search by the soul for what is warranted by the intellect and by the deepest needs of one’s own being.  This has been the meaning of the religions of the world, and this meaning finds its culmination in Christianity.