Experience as a general concept comprises knowledge of or skill in or observation of some thing or some event gained through involvement in or exposure to that thing or event. The history of the word experience aligns it closely with the concept of experiment. The concept of experience generally refers to know-how or procedural knowledge, rather than propositional knowledge: on-the-job training rather than book-learning. Philosophers dub knowledge based on experience "empirical knowledge" or "a posteriori knowledge". The interrogation of experience has a long tradition in continental philosophy. Experience plays an important role in the philosophy of Søren Kierkegaard. The German term Erfahrung, often translated into English as "experience", has a slightly different implication, connoting the coherency of life's experiences. A person with considerable experience in a certain field can gain a reputation as an expert. Certain religious traditions (such as types of Buddhism, Surat Shabd Yoga, mysticism and Pentecostalism) and educational paradigms with, for example, the conditioning of military recruit-training (also known as "boot camps"), stress the experiential nature of human epistemology. This stands in contrast to alternatives: traditions of dogma, logic or reasoning. Participants in activities such as tourism, extreme sports and recreational drug-use also tend to stress the importance of experience.  Types of experience
The word "experience" may refer, somewhat ambiguously, both to mentally unprocessed immediately perceived events as well as to the purported wisdom gained in subsequent reflection on those events or interpretation of them. Some wisdom-experience accumulates over a period of time, though one can also experience (and gain general wisdom-experience from) a single specific momentary event. One may also differentiate between (for example) physical, mental, emotional, spiritual, vicarious and virtual experience(s).  Physical experience
Main article: Physical Property
Physical experience occurs whenever an object or environment changes.  In other words, physical experiences relate to observables. They need not involve modal properties nor mental experiences.  Mental experience
Main article: Mind
Mental experience involves the aspect of intellect and consciousness experienced as combinations of thought, perception, memory, emotion, will and imagination, including all unconscious cognitive processes. The term can refer, by implication, to a thought process. Mental experience and its relation to the physical brain form an area of philosophical debate: some identity theorists originally argued that the identity of brain and mental states held only for a few sensations. Most theorists, however, generalized the view to cover all mental experience. Mathematicians can exemplify cumulative mental experience in the approaches and skills with which they work. Mathematical realism, like realism in general, holds that mathematical entities exist independently of the human mind. Thus humans do not invent mathematics, but rather discover and experience it, and any other intelligent beings in the universe would presumably do the same. This point of view regards only one sort of mathematics as discoverable; it sees triangles, right angles, and curves, for example, as real entities, not just the creations of the human mind. Some working mathematicians have espoused mathematical realism as they see themselves experiencing naturally-occurring objects. Examples include Paul Erdős and Kurt Gödel. Gödel believed in an objective mathematical reality that could be perceived in a manner analogous to sense perception. Certain principles (for example: for any two objects, there is a collection of objects consisting of precisely those two objects) could be directly seen to be true, but some conjectures, like the continuum hypothesis, might...