A brief history of epistemology (IMPORTANT)

Idealism (Plato):   Plato believes that reality is always changing, senses are illusory. Knowledge (episteme) needs to be permanent and unchanging. 

For Plato, knowledge is acquired through anamnesis, which is an innate form of recollection, a sort of hardware we come with (for example, humans come with a memory function already built-in by our brain evolution).

Here comes the idea of Forms. Forms exist independently of us: Think of math, logic, geometry, etc. Plato believes these Forms are "universals." A universal is a property that can be possessed by many things at once. Examples of universals: "goodness," "beautiful," "extended," "redness," "human," etc. See that each applies to many things at once. Take "beauty", it is not a physical concept. So, how do we know it? It's a concept that applies to many different things.

Take a look at Plato's allegory of the CAVE.

Skepticism: An attitude of suspension to the possibility of knowledge or absolute knowledge.

It comes from Pyrrho of Elis (c. 365–275 bc). Pyrrhonists, while not asserting or denying anything, attempt to show that one ought to suspend judgment and avoid making any knowledge claims at all. The Pyrrhonist’s strategy is to show that for every proposition supported by some evidence, there is an opposite proposition supported by evidence that is equally good.


Rationalism:  (Spinoza, Leibniz, Descartes) rationalism is the view that regards REASON as the chief source of knowledge. Rationalism is also a methodology or a theory in which the criterion of the truth is not sense-based but instead deductive.

There is a connection between Skepticism and Rationalism.

Descartes uses skepticism in his Cartesian method. Doubt requires further rational proof. There are three parts: 1- the Dream Argument, 2- the Evil Demon argument and the 3- the Cogito argument (... I can't doubt that I doubt. Therefore I think, therefore I am). The conclusion is that Descartes believes that scientific knowledge can be derived a priori from "innate ideas" through deductive reasoning. Where these "innate ideas" come from? GOD.

Empiricism:  (John Locke, George Bishop, David Hume) Empiricism is the idea that experience as the main source of knowledge. It emphasizes the role of experience and evidence, especially sensory perception.

Here's an interesting video. 

Empiricists believe in inductive reasoning (making generalizations based on individual instances) in order to build a more complex body of knowledge from these direct observations. This is the basis of modern science, and the scientific method, is considered to be methodologically empirical in nature, relying as it does on an inductive methodology for scientific inquiry.

There are two schools: Locke's Representative Realism and Berkeley's Phenomenalism.

For Locke, the world is divided into two qualities: primary qualities, which exist in the object independently of our perception (solid, movement, shape) and secondary qualities, which are dependent of our sense perception (sight, taste, hearing, touch, smell).

Berkeley believes that all qualities are secondary. The result is that there is no world independent of our perceptions, except what he calls unperceived perceptions. These are a bundle of perceptions caused by God.

David Hume's skepticism about cause an effect. Hume is an empiricist, so he believes that only experience gives us knowledge. Ok, this is why he remains skeptical about the idea of causation (every effect has a cause that makes it happen). 

He goes: "Of two events, A and B, we say that A causes B when the two always occur together, that is, are constantly conjoined. Yet, we don't experience A causing B. We take the conjunction for a fact and have a certainty that this conjunction "will continue to happen."

Causality is a posteriori, based on experience. We use induction to justify it. Now, can you conceive of yourself dropping a ball on earth that doesn't fall? YES YOU CAN! So, Hume says: "the contrary of every matter of fact never implies a contradiction." We are left with a weak notion of causal necessity.

Kant's synthesis between Empiricism and Rationalism. Kant takes Hume's challenge. He proposes the following:

a priori: analytic propositions are a priori (independent from experience): "all triangles have three sides," "all bachelors are unmarried males,"

a posteriori: synthetic propositions are a posteriori (based on experience): "Water boils at 100º C," "All creatures with hearts have kidneys."

synthetic a priori: for example, "7+5=12" or "the shortest distance between two points is a straight line."

RATIONALIST SIDE: Kant believes there are categories that we bring with our perceptual apparatuses. They are part of our reason capabilities. Ex: time, space, causation, quantity, quality, relation, modality, etc. He agrees with Hume that these properties are not experienced. They are not in the world. Instead, THEY ARE INNATE, HARDWIRED.

EMPIRICIST SIDE: Kant believes that experience is a posteriori: what the empiricists called SENSE DATA obtained through our senses, which is fundamental for the physical sciences. 


So, Kant's synthesis proves that both Empiricism and Rationalism hold.

STANDARD ACCOUNT OF KNOWLEDGE: Knowledge is justified true belief. 

K = JTB