Suppose that Fred says to you: "The fastest swimming stroke is the front crawl. One performs the front crawl by oscillating the legs at the hip, and moving the arms in an approximately circular motion". Here, Fred has propositional knowledge of swimming and how to perform the front crawl.
However, if Fred acquired this propositional knowledge from an encyclopedia, he will not have acquired the skill[?] of swimming: he has some propositional knowledge, but does not have any know-how[?]. In general, one can demonstrate know-how by performing the task in question, but it is harder to demonstrate propositional knowledge.
Knowledge consists of beliefs about reality. One way of deriving and verifying knowledge is from tradition or from generally recognized authorities of the past, such as Aristotle. Knowledge may also be based upon the pronouncements of secular or religious authority such as the state or the church. A second way to derive knowledge is by observation and experiment: the scientific method. Knowledge may also be derived by reason from either traditional, authoritative, or scientific sources or a combination of them and may or may not be verified by resort to observation and testing.
Knowledge may be factual or inferential. Factual knowledge is based on direct observation. It is still not free of uncertainty, as errors of observation or interpretation may occur, and any sense can be deceived by illusions. 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. For example, all knowledge of the atom is inferential knowledge. The distinction between factual knowledge and inferential knowledge has been explored by the discipline of general semantics.
Roger Bacon, an English alchemist and philosopher of the high middle ages, had this to say about knowledge: "Of the three ways in which men think that they acquire knowledge of things - authority, reasoning, and experience - only the last is effective and able to bring peace to the intellect." Thus knowledge might arise from authority, logic, or experience[?]. Earlier Divine illumination[?] by the grace of God was contrasted by the early Christian church with knowledge gained by reason such as practiced by classical philosophers such as Plato and Aristotle. Experimental knowledge[?] was discounted, for example, by St. Augustine.