•

to know if something is true, we need to know how we know what we know

•

this is actually a difficult question

•

has a massive literature in philosophy

•

what do we mean by knowledge

•

justified true beliefs

•

from very early philosophy people have been skeptical that we can know anything at all

•

Socrates: "I know one thing: that I know nothing."

•

to get around this problem, René Descartes, tried to prove what it was that one could actually prove that one knows

•

how do you show that you indeed know something

•

"I know that I exist because I'm thinking"

•

it could be that you are a brain in a vat

•

you could be dreaming

•

we might all be in a computer simulation set up by a society of the future trying to figure out how things might have gone differently

•

you can't show any of this for certain

•

in theory, as a Cartesian skeptic, you realize you know very few things about the world, e.g. that you exist because you think and 1+1=2

•

in practice, however, you don't want to be a Cartesian skeptic, because it would be very difficult to live life if you doubted everything equally, e.g. that the food you eat or the floor you walk on is not real

•

and if you don't want be a Cartesian skeptic, you need to understand that we know what we know based on evidence we have for different assertions, and how strong that evidence needs to be depends on the reason we need this particular piece of information, e.g.

•

to make a traffic stop requires reasonable suspicion

•

to make an arrest requires probably cause

•

to convict someone of a crime requires evidence that is beyond a reasonable doubt

•

five key types of evidence

•

1. proof

•

anything that can be determined through mathematical or logical reasoning

•

a. logical proofs

•

since thinking imples existence, since I am thinking, I know that I exist

•

b. mathematical proofs

•

1+1=2

•

2. claims

•

statements we have heard or read from others

•

examples

•

New York is American's largest city (true)

•

It takes seven years to digest gum. (false)

•

three things to evaluate claims

•

a. plausibility

•

is it relatively likely

•

b. expertise of the claimant

•

to what extent does the person who made the claim have the ability to know what they are claiming

•

e.g. is the explanation of how a root canal is performed coming from your dentist or a friend

•

c. reliability of the claimant

•

how accurate as the source been in the past

•

how often has the source admitted and correct errors in the past

•

3. experience

•

things we have watched or directly encountered

•

compare to claim which are indirect

•

examples

•

it hurts to touch hot things

•

John ate lunch at noon

•

reliability of observations

•

maybe John was not eating lunch but was having a snack and ate lunch later

•

consider any optical illusions

•

4. inference

•

extensions that we make from other evidence

•

examples

•

object permanence

•

babies think objects go in and out of existence depending on if they are currently experiencing them

•

evolutionary theory

•

making the logical step from observed evidence such as the fossil record to explain what has happened in the past

•

John likes pizza because I saw him eating pizza

•

quality depends on

•

quality of evidence

•

how big the leap of inference is

•

how many times did you see Tom eat pizza

•

5. deductive testing

•

the scientific method

•

the most systematic way we have of gaining information

•

we make a hypothesis, set up a test, and have numerous people who doubt the results test it

•

examples of hypotheses to test

•

acetaminophen outperforms a placebo

•

get two groups and give them both

•

the Earth goes around the Sun

•

gather information about how planets, stars, and Sun moves around in the sky and make deductions

•

the television is not broken

•

make sure it is plugged in

•

make sure the remote control has a battery

•

make sure the battery is not dead

•

quality of testing

•

how rigorously was the scientific method adhered to