March 6th, 2017

How do we know what we know?

  • Do you smoke? Is it healthy? Why?
  • Do you vaccine your child? Why?
  • Do you eat meat? Why?

Do you believe in …

  • Climate change
  • Ghosts
  • Germs
  • Fairies
  • Atoms
  • UFO’s carrying aliens
  • Donald Trump

The source of truth

How do we know what we know

First approach: Perception

We see, we hear: Empirical Truth

We grasp the world with our 8 senses

  • Sense-Certainty
  • see to believe

But …

We dream

Which blue circle is bigger?

How many colors

Are A and B the same color?

Incomplete information

“The Earth is flat”

Our senses can fool us

  • Optical illusions
  • Dreams
  • Incomplete information

Distrust of senses

The body is dirty, the soul is pure

Plan B: Rational view

Truth emerges from Reason

  • Aristotle
    • logic syllogism
  • Euclides
    • geometry
    • axioms
    • theorems


Rational thinking chemically pure

  • feelings are not important, but truth feels good

  • beauty is not important, but truth is beautiful

  • abstraction disconnects from details

Separate Essence from Accident

Truth from authority

  • Medieval/feudal point of view
  • Aristotle was the most intelligent man, he must be right
  • Knowledge is in “The Books”
  • Catholic church was built on him

Political power liked it: a stable society

Question: what about …?

  • St. Thomas
  • St. Agustin
  • Baghdad


Homework 1:

The “official” history is from a European point of view.

What can we say from the Middle-East point of view?

Is rationallity enough?

Extramission theory of vision?

  • A theory accepted by Plato, Euclides and others
  • The eyes emit a “gentle” fire that touches the objects we see
  • We need to mix with another fire to see
    • like the sun
    • or a campfire

Geocentric model of the planets

Four elements

Fire, earth, water and air

  • All material is a mix of these four elements
    • Ex. Wood is made of fire and earth
    • Burning wood separates the fire, leaving only earth (ash) behind

Humour theory

Excess or deficiency of any of four distinct bodily fluids (humours) influences temperament and health

  • Classic Greek, Roman, Persian and Indian (Ayurveda)
    • Blood, Yellow bile, Black bile, Phlegm
  • Hippocrates (born c. 460 B.C.E.)
  • Galen (b. 129C.E. Asia Minor)
  • Bloodletting used until the 19th century

Today: Conspiracy theories

  • Apollo moon landings were staged
  • Weather control
  • GMO research is fake
  • Roswell UFO incident
  • Area 51
  • Kennedy assesination
  • 9/11

Homework 2

What other things are believed by smart people despite evidence on the contrary?

What Aristotle did not knew

The age of discoveries showed that the old books did not have all answers

  • What about America?
  • What about Australia?


Where is the Truth?

The Truth is Out There