This article develops an interpretation and defense of Husserl’s transcendental-phenomenological reduction by thematizing the absoluteness of consciousness as the ground for philosophical science. Tracing the different routes into the reduction, I examine how two aspects of the absoluteness of consciousness—its indubitable existence and its non-relativity—are inextricably connected for grounding science. I then defend each of these senses of absoluteness. I argue that it is a countersense to reduce one’s own experience to an illusion with no ontological significance, that is, to nothing. I then consider whether the structures and components of consciousness necessarily implicate its relation to an external reality, thus relativizing it, demonstrating that they do not. I claim that the reduction, as motivated by the absoluteness of consciousness, is therefore essential to phenomenology’s scientific ambitions.