Declarative knowledge

Descriptive knowledge, also declarative knowledge or propositional knowledge, is the species 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, that is, the knowledge of how, and especially how best, to perform some task.

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.

Acquiring knowledge
People have used many methods to try to gain knowledge.


 * 1) By reason and logic (perhaps in cooperation with others, using logical argument).
 * 2) By mathematical proof.
 * 3) By the scientific method.
 * 4) By the trial and error method.
 * 5) By applying an algorithm.
 * 6) By learning from experience.
 * 7) By an argument from authority, which could be from religious, literary, political, philosophical or scientific authorities.
 * 8) By listening to the testimony of witnesses.
 * 9) By observing the world in its "natural state"; seeing how the world operates without performing any experiments.
 * 10) By acquiring knowledge that is embedded in one's language, culture, or traditions.
 * 11) By having a divine illumination or revelation from a divine agency.
 * 12) By some claimed form of enlightenment following a period of meditation. (For example, the Buddhist enlightenment known as bodhi)
 * 13) By dialogical enquiry (conversation). See Gadamer, Bohm, Habermas, Freire, on dialogue, learning and knowledge acquisition/negotiation: http://www.infed.org/biblio/b-dialog.htm

Types of knowledge
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.

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. 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.

Knowledge in various disciplines
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 mathematics (which generates proofs).

Knowledge in science and engineering
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 steps are peer review and publication, through which the results are distributed to other scientists.

A hypothesis that has been shown to accurately and reliably predict and characterize some physical phenomenon, and has 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 a bridge will hold up. This is one case where new knowledge is generated from scientific knowledge by specialising it to an individual instance.

Knowledge in history
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.

Additionally, the scientific method is essentially the application of the inductive approach to investigation. This approach is entirely appropriate for exploration of the causal world of nature (physics, chemistry, etc.) but not valid for the teleological social sciences, which includes history. There are no constants in human relations, only unmeasurable and inconstant subjective valuations. Electrons always behave the same way under the same conditions, but humans do not -- different people react differently and the same person might react differently at different moments in time. Thus, only spurious inferences can be drawn from repeated observations of human behavior. It might be observed that most humans prefer wealth to poverty or life to death, but it would be invalid to infer any universal law of human behavior from this.

Historians often generate different interpretations of the same event, even when reading the same primary sources, and these interpretations are always subject to revision by other historians. This is because, as a social scientist, the historian must constantly make subjective judgements of relevance in trying to interpret historical events.

Situated knowledge
See Knowledge.

Issues
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.

Non-scientific methods
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.

Practical limits for obtaining knowledge
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, require 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.

"Of the three ways in which men think that they acquire knowledge of things&mdash;authority, reasoning, and experience&mdash;only the last is effective and able to bring peace to the intellect." (Roger Bacon, English alchemist and philosopher)