Husserl declares that mental and spiritual reality possess their own reality independent of any physical basis . Husserl declares that mental and spiritual reality possess their own reality independent of any physical basis , and that a science of the mind ( ` Geisteswissenschaft ' ) must be established on as scientific a foundation as the natural sciences have managed : `` It is my conviction that intentional phenomenology has for the first time made spirit as spirit the field of systematic scientific experience , thus effecting a total transformation of the task of knowledge . ''