% Epistemology
% Mort Yao
% 2017-02-06

*Epistemology* is the study of knowledge.

* *Empiricism* claims that knowledge comes from sensory experience (perception), that is, empirical evidence.
* *Rationalism* regards reason as the chief source and test of knowledge; it claims that any reliable knowledge requires a justification.
* *Skepticism* questions the possibility of certainty in knowledge; it claims that it is not possible to have an adequate justification of knowledge.

For a rationalist, as all knowledge needs to be justified, the *regress problem* emerges: a proposition requires a justification, but any justification itself requires support (i.e., further justification), thus the justification chain goes forever. In response to the regress problem, the justification of beliefs can take very different approaches:

* *Foundationalism*, where a statement is inferred from a basis of unprovably sound premises ("foundations").
* *Coherentism*, where a statement holds true as long as it coheres with all other justified beliefs, including itself ("coherent truth").
* *Infinitism*, where a justification chain is allowed to be infinite, thus there could never be adequate justification for any statement in the chain.

Foundationalism is often related to *constructivism*, which claims that knowledge is a compilation of human-made constructions rather than objective truth. The corresponding approach in the philosophy of mathematics is called *intuitionism*.

# Knowledge and Science

Traditionally, *knowledge* is defined as "*justified true belief*". However, this definition has been questioned by the *Gettier problem*.

Based on the role of empirical evidence in reasoning, knowledge may be divided into two categories:

* *A priori* knowledge, which is independent of empirical evidence, e.g., mathematics, logical deductions.
* *A posteriori* knowledge, which is dependent of empirical evidence, e.g., statistics, statistical learning.

*Science* is the approach to filter out unreliable knowledge and gather together reliable knowledge (either a priori or a posteriori) as a *scientific theory*, by means of inference. The *demarcation problem* concerns what qualifies as science.

# Hypothesis

A *hypothesis* is a proposed explanation or prediction method for a phenomenon. Only formally proved or statistically tested hypotheses may become reliable knowledge.

**Epicurus' principle of multiple explanations.**
If multiple hypotheses are consistent with the observations, one should retain them all.

**Occam's razor.**
Among all hypotheses consistent with the observations, choose the simplest.