Initially, I will show how Wundt's logical theory of mental processes became weaker, according with the successive re-elaborations of his theory of perception presented in the distinct editions of his Textbook of Human Physiology, as well as in some articles. Then I will present his rejection of the unconscious, together with the justification given in the Grundzüge, relating it to the emergence of a new theory of consciousness. Finally, I will discuss the philosophical roots that motivated him to introduce this conceptual rupture within his project of scientific psychology.