Propositional knowledge or declarative knowledge is knowledge that some proposition is either true or false. This distinguishes propositional knowledge from know-how[?] or procedural knowledge[?], which is the knowledge of how to perform some task. This article discusses propositional knowledge from a variety of perspectives, including philosophy, science, and history.
What is the difference between knowledge and beliefs? 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 Knowledge (philosophy) discusses the view of philosophers on how one can tell which beliefs constitute actual knowledge.
There are many methods people use to try to gain knowledge from. All of these are to various degrees controversial:
Knowledge can be classified into 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. See a priori and a posteriori knowledge for more.
Often knowledge is gained by combining or extending other knowledge in various ways. Isaac Newton famously wrote: "If I have seen further than others, it is by standing on the shoulders of giants".
There are many different disciplines that generate beliefs that can be regarded as knowledge. They include science (which generates scientific theories), law (which generates verdicts), history (which generates history), and maths (which generates proofs).
Scientists attempt to gain knowledge through the scientific method. In this method, scientists start by finding a phenomenon of interest, which generates questions. A scientist then picks a question of interest, and based on previous knowledge, develops a hypothesis. The scientist then designs a controlled experiment which will allow her to test the hypothesis against the real world. She then makes predictions about the outcome of the test, based on the hypothesis.
At this point the scientist carries out the experiment, and compares her predictions with her observations. Assuming that there were no flaws in the experiment, then if they match, then this is evidence in favour of the hypothesis. If they do not match, then the hypothesis has been falsified. The next step is peer review, in which the results are distributed to other scientists.
A hypothesis that have been shown to accurately and reliably predict and characterize some physical phenomenon, and had been sufficiently peer-reviewed and tested, may become a scientific theory. Scientific theories are widely regarded as knowledge, though they are always subject to further revision or review should new data come to light.
To use scientific theories, they must be applied to the specific situation in hand. For example, a civil engineer might use the theory of statics (a branch of physics) to determine whether or not a bridge will hold up. This is one case where new knowledge is generated from scientific knowledge by specialising it to an individual instance.
The scientific method does not apply to history (or related disciplines, such as archeology), because it is not possible to construct experiments to test theories. Suppose a historian believes that Napoleon would have won the Battle of Waterloo if Gebhard Leberecht von Blücher had arrived an hour later. The historian cannot simply re-run the battle and see what would happen with different starting conditions[?].
Knowledge is often situated. Knowledge gained in one situation cannot always be relied on in another situation. Imagine two very similar breeds of mushroom, which grow on either side of a mountain, one nutritious, one poisonous. Relying on knowledge from one side of an ecological boundary, after crossing to the other, may lead to starving rather than eating perfectly healthy food near at hand, or to poisoning oneself by mistake.
Some methods of generating knowledge, such as trial and error, or learning from experience[?], tend to create highly situational knowledge. One of the main benefits of the scientific method is that the theories it generates are much less situational than knowledge gained by other methods.
What constitutes knowledge, certainty and truth are controversial issues. These issues are debated by philosophers, social scientists, and historians. Ludwig Wittgenstein wrote "On Certainty" - aphorisms on these concepts - exploring relationships between knowledge and certainty. A thread of his concern has become an entire field, the philosophy of action.
There are a number of problems that arise when defining knowledge or truth, including issues with objectivity, adequacy and limits to justification. Beliefs are also very problematic not least because they are either true or false, and therefore cannot be adequately described by conventional logic. An action likewise can be taken or not, but there is the troubling idea of an "event" is, an action taken by nobody, or nobody who you can blame.
Some people hold that science does not actually tell us about the physical world that they live. They hold that the world cannot be understood by science, but rather by religious revelations, mystical experience, or literary deconstructionism.
What we hold to be knowledge is often derived by a combination of reason from either traditional, authoritative, or scientific sources. Many times such knowledge is not verifiable; sometimes the process of testing is prohibitively dangerous or expensive. For instance, some physics theories about the nature of the universe, such as string-theory, requite the construction of testing equipment currently beyond our technology. Since such theories are in principle subject to verification or refutation, they are scientific; since they are not proven experimentally, they are not considered certain knowledge. Rather, in such cases we have certain knowledge only of the theory, but not of what the theory describes.