Whatever we can either know or achieve, is _our_ truth, _our_ act presented in and through our self-consciousness. It is impossible for us to conceive any standard of truth or object of desire outside of our experience. As a thinking and acting being man pursues ends, and has the consciousness that they are his own ends, subject to his own choice and control. It is always the self that the soul seeks; and the will is nothing else than the man making and finding for himself another world. The attempt has recently been made to measure mental states by their physical stimuli and explain mental {85} processes by cerebral reaction. It is true that certain physical phenomena seem to be invariably antecedent to thought, but so far science has been unable to exhibit the form of nexus between these physical antecedents and ideas. Even if the knowledge of the topography of the brain were immeasurably more advanced than it now is, even though we could observe the vast network of nerve-fibres and filaments of which the brain is composed, and could discern the actual changes in brain-cells under nerve stimulations, we should still be a long way off from understanding the nature and genesis of ideas which can only be known to us as immediate in their own quality. All that we can ever affirm is that a certain physical excitation is the antecedent of thought. It is illegitimate to say that it is the 'cause' of thought; unless, indeed, the word 'cause' be invested with no other meaning than that which is involved in such a conception. It is, however, in a very general way only, and within an exceedingly narrow range, that such measurement is possible. We do not even know at present what nerves correspond to the sensations of heat and cold, pain and joy; and all attempts to localise will-centres have proved unavailing.