Propositional knowledge

Descriptive knowledge, also declarative knowledge or propositional knowledge, is the type of knowledge that is, by its very nature, expressed in declarative sentences or indicative propositions. This distinguishes descriptive knowledge from what is commonly known as "know-how", or procedural knowledge (the knowledge of how, and especially how best, to perform some task), and "knowing of", or knowledge by acquaintance (the knowledge of something's existence).

The difference between knowledge and beliefs is as follows: A belief is an internal thought or memory which exists in one's mind. Most people accept that for a belief to be knowledge it must be, at least, true and justified. The Gettier problem in philosophy is the question of whether there are any other requirements before a belief can be accepted as knowledge.

The article epistemology discusses the opinion of philosophers on how one can tell which beliefs constitute actual knowledge.

People have used many methods to try to gain knowledge.

Knowledge can be classified upon a priori knowledge, which is obtained without needing to observe the world, and a posteriori or empirical knowledge, which is only obtained after observing the world or interacting with it in some way.

Often knowledge is gained by combining or extending other knowledge in various ways. Isaac Newton famously wrote: "If I have seen further... it is by standing on the shoulders of giants".

Inferential knowledge is based on reasoning from facts or from other inferential knowledge such as a theory. Such knowledge may or may not be verifiable by observation or testing. The distinction between factual knowledge and inferential knowledge has been explored by the discipline of general semantics.

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