Justified True Belief

(●) Acquaintance Knowledge (Knowing-by-acquaintance): Knowing something because the object of knowledge is directly present to one’s consciousness. For example, Dan knows the ball in front of him because he sees it and is directly aware of it...he knows it by sensory intuition. In this context, intuition does not mean a guess or irrational hunch, but rather a direct awareness of something present to consciousness. People know many things by acquaintance or intuition, such as their own mental states (thoughts, feelings, sensations), physical objects they perceive through the five senses, and, according to some, even basic principles of mathematics. When asked how people know that 2 + 2 = 4 or that if it is raining outside then it must be wet outside, the answer seems to be that people can simply “see” these truths. This kind of “seeing” is often thought to involve an intuitional form of awareness or perception of abstract, immaterial objects and the relationships among them...such as numbers, mathematical relations, propositions, and the laws of logic. Thus, all these examples are arguably cases of knowledge by acquaintance.

(●) Procedural Knowledge (Knowing-how): The ability or skill to behave in a certain way and perform some task or set of behaviors. One can know how to speak Greek, play golf, ride a bicycle, or perform a number of other skills. Know-how does not always involve conscious awareness of what one is doing. Someone can learn how to do something by repeated practice without being consciously aware that one is doing the activity in question or without having any idea of the theory behind the practice. For example, one can know how to adjust one’s swing for a curve ball without consciously being aware that one’s stride is changing or without knowing any background theory of hitting technique.

(●) Propositional Knowledge (Knowing-by-description): This is knowledge of facts or truths, expressed in declarative sentences. For example, "I know that water boils at 100 degrees Celsius." It is the most discussed type in philosophy and is often analyzed as "justified true belief."