Forms of knowledge

Knowledge can be classified in several ways. Firstly, it can be either explicit (self-conscious) or implicit (tacit, hidden from self-consciousness). Secondly, it can be either propositional or non-propositional (something which cannot be represented by propositions, e.g. knowing how to do something?). Propositional knowledge can further be divided into empirical or a posteriori and non-epirical or a priori knowledge. This division is usually associated to rationalism and empirism: rationalists like Descartes, Leibniz and Spinoza believed that all knowledge about real world is a priori, while empirists like Locke, Berkeley and Hume believed it is a posteriori.

Kant tried to combine the rationalistic and empiristic traditions. He believed that a priori knowledge is independent of any experience, and based on pure understanding and reason. It is also necessary, like logical or mathematical truths (especially tautologies). A posteriori knowledge is based on experience and thus contingent (we don't have direct access to material world). The knowledge is represented as judgements, which can be analytic or synthetic. Analytic judgements explain, but they don't enlarge our knowledge. Synthetic judgements really enlarge our knowledge by adding new contents. Kant argued that mathematical, physical and metaphysical judgements are synthetic a priori, i.e. they enlarge our knowledge and are based on reason. (This seems to be the heighest category: new knowledge, which is necessary!)

Locke has constucted a more complex view, which adds intuitive element to empirism and rationalism. He has distinguished three types of knowledge: 1) knowledge based on perceptions i.e. empirical knowledge, which is not necessary but only probable, 2) intuitive knowledge, which concerns our own being and is doubtless, and 3) demontsrative knowledge, which is based on proofs, i.e. rational knowledge. Primary ideas are produced by our perceptions or self-study, and more complex ideas are derived from them by combining, abstracting and creating relations between them. (Question: what about demonstrative knowledge? Is it derived from empirical and intuitive knowledge? Are all complex ideas demonstrative knowledge?)

Classical definition

The classical definition of knowledge (by Socrates) as "justified true belief" concerns only propositional knowledge. However, scientific knowledge is propositional by its nature (could it be something else?), and thus it is relevant to consider this definition more carefully. (An interesting question is, how to define non-propositional knowledge?!)
  1. Knowledge is belief: If you know p, you also believe p (but not vice versa). This hints that the knower has some psychological relation to known proposition. This psychological state can exist even if it is not manifested. It is noteworthy that not all beliefs are knowledge: the beliefs can also be false.
  2. Knowledge is true belief: Truth seems to be a necessary condition for knowledge, but it is really hard to define universally. In correspondence theory truth is defined as correspondence between the proposition and the actual proposition. But how to check the actual proposition? Do we have any direct access to reality? This demostrates that epistemology is strongly connected to ontology, i.e. what we consider as being or modes of being. Coherence theory requires only that the proposition is consistent with the other system (i.e. it doesn't cause contradiction). Obviously, this is minimal requirement for truth, but hardly satisfactory. According to pragmatic view truth is defined as usefulness: truth is what works best in reality. Naturally, usefulness depends on who has defined it: it can measure economical profit, or diversity of political opinions. This definition also holds largely in empirical science: the theory which predict future events best, is considered the most probable or "true" theory.
  3. Knowledge is justified true belief: The point is that truth is not enough - it could be pure guess. The knower must have adequate indication that the proposition is true - i.e. evidence. Alston defines justification as "what is epistemically good for maximizing truth and minimizing falsity". This adds another side to analysis: we want to get assured about the truth of proposition, but in the same time eliminate its falsity.
Crisholm (Theory of knowledge, 1966) has speculated the third classical criteria of knowledge, namely justification. He argues that we cannot say that the knower "has adequate evidense", but that something "is evident" for her/him. He tries to justify this by explaining that the subject can have adequate evidense, even if s/he doesn't know that s/he knows. However, his own formulation produces same problems, as he himself states: some propositions can be evident to the subject, and still the subject doesn't know that they are true. He also speculates how to define "evident" and finally selects "more reasonable" (i.e. if believing is more reasonable than withholding, it is evident). Crisholm's speculations are so senseless and self-contradictory that they are not even worth of disarguing here.

Scientific knowledge

To be scientific the knowledge must be The scientific methods should also fill some criteria, which try to guarantee quality of scientific knowledge. (These are important and quite permanent part of general paradigm of science):