Epistemology is the second major branch of philosophy. It is the science that studies the nature and means of human knowledge.
Whereas Metaphysics asks, "What is truth?" Epistemology inquires, "How do we know the truth?"
Epistemology defines man's relationship with his mind. In order to address this relationship, one must first study the bridge between metaphysics and epistemology, which means between reality and reason. The two components of this bridge are sense perception and volition.
Consciousness as previously defined is the awareness of the existence of both the self and external reality. The means of this awareness are the senses. Thus, the senses are a corollary of the axiom of consciousness. They are the means by which an individual is aware, the cause of Consciousness. Because the Principle of Consciousness is dependent upon the senses, these are self-evident primaries of cognition without which all thought and understanding would be impossible.
Any philosophical attack on the validity of the senses automatically negates itself, since the content of the attack must rely on concepts that are themselves constructed from percepts (thought-data perceived through the senses) that were acquired through the senses. Most attacks on the fundamentals of knowledge fall unavoidably into pits of self-contradiction.
Consciousness does not create its own content (subjectivism) or even the sensory forms by which it obtains its content. Those forms are determined by the perceiver's senses physically interacting with external reality in accordance with causality. The source of sensory form is thus not consciousness, but existential fact independent of consciousness. In other words, the source of sensory form is the metaphysical nature of reality itself that is then biologically converted into mental concepts, discussed below.
The first stage of consciousness is that of sensation, which is an irreducible state of awareness produced by the action of a stimulus on a sense organ. The most primitive conscious organisms, as well as newborn infants, possess only the capacity of sensation. Over time, the human brain enters the second stage of consciousness as it automatically integrates sensations into percepts, which are the brain's internal representations of external entities. This automatic percept-formation is a metaphysically given absolute; the moment a stimulus creates a sensation it is automatically interpreted by the brain. Thus, any discussion of human knowledge (associated with mental comprehension) must begin with percepts, not sensations, as the base of cognition.
"Focus" in the conceptual realm means a quality of purposeful alertness in a person's mental state. Focus is the state of a goal-directed mental process committed to attaining full awareness of a particular subject. Until a mind is in focus, its mental machinery is unable to function in the human sense--to think, judge, or evaluate. The choice to focus is thus the irreducible primary choice on which all other choices depend. It is a first cause within a consciousness, not an effect of preceding causes.
Infants can begin to process information and learn only after they have gained this ability to focus.
Man chooses to focus his consciousness or not. This is the first cause in a lengthy chain, and the inescapability of such choice expresses man's essential nature. On this basis, he forms the mental content and selects the reasons that will govern all his other choices. Man chooses the causes that shape his actions.
Even volition is a corollary of the axiom of consciousness. Because one can choose to focus on the barest of facts (Existence), then free will is actually axiomatic to some degree. Although few will argue that external sources fail to influence the human mind, the existence of the will is undeniable.
Determinism is the assertion that the individual possesses no free-will to choose what he will do. Yet like any rejection of a philosophic axiom, determinism is self-refuting. Just as one must accept existence or consciousness implicitly in order to deny either of them, so one must accept volition in order to deny it.
The will is a product of the conceptual faculty; the faculty of reason is the faculty of volition.
Thus, the Senses allow entities to become Conscious. Humans are conscious, thus sensory must be valid on a basic level. Of course, the senses can be fooled; yet means other than the senses can be used to further verify reality (tools of measurement such as microscopes, infrared detectors, etc). If the most basic sense information can be trusted, then all other sensory data can come from artificial extensions of what we observe.
Free volition must also exist in a basic form, for the mind can inevitably decide on what it should focus. Combining this and the above assertion allows human investigators to trust conclusions derived from evidences observed by the senses and human inventions.
Thus we arrive at the Senses and Volition, the primary faculties that allow the mind to evaluate according to reason.