This volume has undergone many changes. When it appeared in 1878 it was little more than a history of the concepts we have already referred to.[87] But at the present time it deals with the history of the concepts, a criticism of these, and finally the presentation of the author's own thesis regarding the reality of an independent spiritual life. 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.