Class 9: How do we know what we know?

Methodology of Scientific Research

Andrés Aravena, PhD

March 19, 2024

How do you know?

Tell me…

Do you smoke?

Is it healthy?


How do you know?

Tell me…

Did you get vaccinated?


How do you know?

Do you believe in UFOs and aliens?

Do you believe in Ghosts?

Do you believe in Fairies?

Do you believe in Germs?

Do you believe in Atoms?

How do we know what we know?

First approach: Perception

Seeing is believing

We see, we hear, we have an Empirical Truth

Philosophers say “Sense-Certainty”

We perceive the world with our 8 senses
(which senses?)

But …

Are they parallel?

Are they parallel?

Which blue circle is bigger?

Which one is bigger

How many colors are here?

Which one is darker?

Black or white dots?

Do the lines cross?

Do the circles cross?

Is this a movie?

Does this move?

Does this move?

Does this move?

Does this move?

Does this move?

We cannot trust our senses

We can have optical illusions

Moreover, sometimes different people see differently

Which color is the dress?

For more information

Google “The Dress”, and watch “The Dress is Bloie”

Illusions are not only optical

Put one hand in hot water, the other in cold water

Then put both in warm water

Is it hot or cold?

Perception depends on our expectations

Have you ever seen someone that was not there?


We dream

and we don’t know that we are dreaming

We cannot trust our memory

Déjà vu:
feeling as if one has lived this moment before

False memories can be implanted

See, for instance

  • Michaelian Kourken “Confabulating, Misremembering, Relearning: The Simulation Theory of Memory and Unsuccessful Remembering”. Frontiers in Psychology 7 (2016) DOI 10.3389/fpsyg.2016.01857

  • The work of Elizabeth Loftus

Our mind cannot be trusted

When we dream,
we don’t know that we are dreaming

We forget, and we forget that we forget

Working with Incomplete information

“The Earth is flat”

We only see part of reality

Our experience is limited

At our scale

  • the Earth is flat
  • mountains never change
  • germs do not exist
  • atoms do not exist

Our vision is “local”

Our friends are like us. It seems that everybody agrees with us

We only see our neighborhood of the network, where everybody looks like us

The Earth looks flat

  • Today some people believe that Earth is flat
  • Some people believe that old people believed the Earth is flat

Homework: Is the Earth flat?

What experiment can we do to see if the Earth is flat or not?

What is wrong with the geocentric model?

What can we do to see if the Earth rotates on it axis?

Write your answer in a document

Assigning meaning where there is none


Humans are good at finding patterns

(even in our kitchen)

Even when there is no pattern

This is called “Pareidolia”


Humans are “pattern-matching machines”

What is happening here?


Our senses can fool us

  • Optical illusions
  • Dreams
  • Hallucinations
  • Incomplete information
  • Pattern matching
  • Anthropomorphism

Distrust of senses

This leaded some people to believe that

“The body is dirty,
the soul is pure”

We need a “Plan B”

That will be the topic of next class