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Philosophy is a fascinating subject, studying some of the most diverse and fundamental questions. It’s a deep subject, yet a fun and stimulating one. Each of us has done a significant amount of philosophy, even if we aren’t aware of it.

What is philosophy?

Philosophy is the study of knowledge, ethics, freedom, logic, metaphysics and other fundamental problems. It addresses important, complex and highly debated questions


Ethics is the study of morality and choices.

What makes some actions good and other bad? Is morality just an convention? Can we find an universal definition of morality or is it subjective? Do we need God for absolute moral standards?


Formally known as epistemology, this branch of philosophy revolves about knowledge.

What is knowledge? Cam we “know” something? What is required to know something? Are there any limits to our knowledge? Where does knowledge come from:

  • Reason and logic ?
  • Intuition ?
  • Feelings ?
  • Experiences ?

Is science knowledge or is it just the currently accepted theory?


Are we free to make all choices or do we follow a cosmic plan, a Godly plan, the laws of Nature ? What are the limits to our freedom? Should we voluntarily restrict our freedom (for the greater good) ?


Logic is the study of relationships between propositions. It teaches us how to evaluate arguments and check their validity. More specifically, it studies inferences, deductions and the structure of valid arguments.


What is reality? Is the physical world just an illusion? Are our senses trustworthy? What can we be sure of? Are we in a dream? Are we in the Matrix?

Why should we study philosophy?

Why shouldn’t we study physics, take a walk or try a new recipe? Even if these are all interesting and fun, philosophy attacks the most important and fundamental questions one can ask ourselves. It is fun and stimulating! It opens your mind to new opinions and ideas. It makes you a critical thinker and you learn things about yourself and the world.

Fundamental questions

Philosophy studies some of the most important and fundamental questions. These answers may radically influence your approach to life.


  • Does God exist?
  • Does your life have a purpose?
  • Are you free to make choices?

Discovering ourselves and the world

Through philosophy, you will learn a lot about yourself and others. You will view things in a different manner. You will be more open-minded, tolerant and ready to understand new ideas and surprising points of view. It will allow you to be a better person, by avoiding common pitfalls that lead to disrespectful and negative attitudes.


One of the most important reasons for studying philosophy is fun! If you don’t have fun while discovering these new ideas, tearing them apart and rebuilding them, move on and choose another activity that will suit you better. However, I believe you will think of philosophy as an extremely fun and entertaining activity.

Intellectual stimulation

Philosophy, through its exploration of various subjects, is very stimulating and fun. A interesting exercise when studying a new subject is to:

  • explore what your intuition and your current beliefs are. Then criticize them, try to find weaknesses in your beliefs.

  • explore the different points of view and see how they fare against each other. In others words, make a debate where you take various positions and try to defend them.

What philosophy isn’t

Philosophy uses rationality and careful arguments. It is based on sound reasoning, trying to make good arguments and to use logical thinking . It tries to be the clear, logical and organized.

  • Philosophy isn’t just random babbling.
  • Philosophy isn’t a waste of time.
  • Philosophy isn’t a useless subject.

Random babbling

Many people think that philosophy is just people talking about useless subjects, in a way that is incomprehensible to most people. They just talk and talk, without ever reaching a conclusion or getting things done.

However, this is simply false. Philosophy may be a bit harder to understand when you’re deep into a discussion, because a lot of jargon is used to shorten the discussions. However, what they discuss is, with a bit of training and a will to learn, very interresting. These ‘endless discussions’ are actually great debates in which ideas are analysed and dissected. They are very meaningful and some really good points or conclusions are (tried to be) reached.

Waste of time and a useless subject

To some people, philosophy cannot reach any conclusions. They claim it is just a series of endless discussions. They find it pointless and believe that you could spend your time better by doing other (more important) things.

Even if philosophy can’t state universal truths (or can it?), it allows us to understand the various possibilities and points of view about some of the most fundamental questions. It examines their strengths and weaknesses. It analyses theories and tries to find arguments against it and in its favour.

Through this thorough examination, it helps you understand a lot and reject false theories. Through the various points of view you get from it, it changes your approach to life, since philosophy is about fundamental questions.

As a bonus, philosophy is fun, very stimulating and helps you think clearly about others things that philosophy, such as business plans, current news events and personal events in your life. It is a very effective tool to sharpen your intellectual abilities .


Knowledge may be the most important branch of philosophy, since all others depend on it. If we were to conclude that knowledge is impossible, it would considerably change philosophy and its theories.
Let’s get you started!

Note: In this section, were are going to treat propositional knowledge (e.g. Paris is the capital of France.). There are other types of knowledge …

  • Practical knowledge (e.g. I know how to tie my shoelaces.)
  • Knowledge through contact (e.g. It know the mayor of New York)
    … but these are of least interest now.

What is knowledge ?

This is a very difficult question. To break down it a little, let’s say that knowledge is the set of all propositions that can be known. Then, if we can decide if we know something, we can make such a repertoire.This allows us to transform the question into ‘What does it take to know something?’.

From the answer to that question, knowledge is the set of all propositions which respect these conditions.

What does it take to know something ?

Given some proposition P, how do we know if a subject S knows that proposition P? In other words, what are the necessary conditions to say that S knows P?

True Justified Belief

One of the first and long-standing answer is true justified belief. It is credited to Plato and his numerous discussions.

It claims that to know something, we must believe in a true proposition and have a suitable justification.

Finally, we will give an answer to his objections.

Condition 1. Truth

The first obvious necessary condition is truth. I can’t know that 2 + 2 = 5, since this is false.

If you say ‘Computers are made of dirt’, do you know it? No, because the proposition P you claim to know is false.

Most philosophers agree with that truth is necessary. We will then accept if for now as such.

Condition 2. Belief

Another condition is belief. Yes, belief. It surprised me too when I heard it. What has belief to do with knowledge? Aren’t they opposites?

But it is obvious: to know p, you must believe in p.

Some philosophers refute this, such as Colin Radford. For more information, consult the article on the Stanford Encyclopedia of Philosophy.

Condition 3. Justification

Imagine that I have a coin in my hand. I say ‘I know that it will turn up heads’. Then, when I flip it, by chance, it’s heads. Did I know it?

No! It was merely luck. It was just a coincidence. I had no reason to favor heads instead of tails . I had no justification behind my pseudo-knowledge.

The same applies if I say that 27th January 3842, it will be a rainy day. By chance, it’s a rainy day. Did I know it? Again, no! I had no justification behind my knowledge.

From these example, it appears that justification is another necessary condition to knowing things.

Gettier problem

Edmund Gettier, in his famous ‘Is Justified True Belief Knowledge?‘ article, relaunched the whole debate.

He gave counter-examples which obey the 3 conditions and yet most people would agree that there is no knowledge (the Gettier Problems).

Russel’s Example

Bertrand Russel

Bertand Russel, an English philosopher, created a simpler example that illustrates the same problem:

Everyday you wake up and you go to school. In the small village where you live, there is a church and a clock on it. The clock has been reliable for a long time. Today, when you go by, it shows 8 o’clock. Here’s the twist: by pure luck, the clock broke yesterday at precisely 8 o’clock.

Following the traditional definition of knowledge, do you know its 8 o’clock?

  1. Belief: You believe it’s 8 o’clock.
  2. Truth: It actually is 8 o’clock.
  3. Justification: The clock always worked in the past and so its reliable.

All the conditions are met, and yet it doesn’t seem to be knowledge. We didn’t know it was 8 o’clock. This seems to suggest that these conditions might be necessary but not sufficient. Where is the problem? The example or the theory?

Gettier’s examples are more complex than Russel’s !

Example 1

Smith has applied for a job, but, it is claimed, and he has a justified belief that “Jones will get the job”. He also has a justified belief that “Jones has 10 coins in his pocket“.

Smith therefore concludes (by the rule of the transitivity of identity) that “the man who will get the job has 10 coins in his pocket“.

In fact, Jones does not get the job. Instead, Smith does. However, as it happens, Smith (unknowingly and by sheer chance) also had 10 coins in his pocket. So his belief that “the man who will get the job has 10 coins in his pocket” was justified and true. But it does not appear to be knowledge.

Example 2

Smith, it is claimed by the hidden interlocutor, has a justified belief that Jones owns a Ford”. Smith therefore (justifiably) concludes (by the rule of disjunction) that “Jones owns a Ford, or Brown is in Barcelona, even though Smith has no knowledge whatsoever about the location of Brown.

In fact, Jones does not own a Ford, but by sheer coincidence, Brown really is in Barcelona. Again, Smith had a belief that was true and justified, but not knowledge.

Answer: False Premises

In both examples, the conclusion rests upon on a invalid justification for his belief :

  • “Jones will get the job” (in example I)
  • “Jones owns a Ford” (in example II)

Since the justification is wrong, his beliefs weren’t correctly justified. Then, the theory say he doesn’t have knowledge, solving the entire knowledge.

A general solution to this kind of problem is to say that the justification must be valid and true.

This also solves more complicated and subtle problems, such as the example given.


After arranging to meet with Mark for help with homework, Luke arrives at the appointed time and place.

Walking into Mark’s office, Luke clearly sees Mark at his desk and forms the belief ‘Mark is in the room. He can help me with my logic homework’. This belief is justified since he clearly sees Mark at his desk.

However, it’s not Mark that Luke saw. it was a marvelous hologram, perfect in every respect, giving the appearance of Mark at his desk.
Nevertheless, Mark is in the room, but crouched under his desk reading Frege.

Luke’s belief that Mark is in the room is true (he is in the room, under his desk) and justified (Mark’s hologram is giving the appearance of Mark hard at work).

Same problem, but hidden

Let’s decompose the justification:

  1. It looks like Mark is in the room.
  2. Since it looks like Mark is in the room, Mark is in the room.
  3. Therefore, Mark is in the room.

Here the problem becomes evident, because we uncovered a hidden premise. The 2nd premise is false, since obviously the hologram can make it look like Mark is in the room while he isn’t there.

Since the 2nd premise is false, the conclusion is false. Therefore, the justification is invalid. Our theory of knowledge still stands!

Theories of Knowledge

Over the centuries, philosophers have studied knowledge in great detail. Various theories about knowledge have been developed, describing its structure, origins and limits.

Descarte’s rationalism and Hume’s empiricism are among the most famous ever developed. They are very diferent from one another. We’ll let you compare!

Descartes’s rationalism

René Descartes was a French philosopher, who researched the nature of knowledge and a way to discover it. His main tool was reason.

If he could doubt something, he rejected it. He continued until he found an indubitable statement. Then, he build knowledge using that statement as his foundation, his basis.

His main tools were doubt, reason and a particular view of knowledge: foundationalism.

The importance of doubt

We hold an incredible amount of beliefs and knowledge. We have beliefs about gardening, politics, personal relationships and life itself. These beliefs shape our lives and have a crucial impact on our decisions. They are the hidden tools on which we rely to make our daily decisions in a sensible manner. However, we all know the we hold some false beliefs. As the proverb says: No one is right about everything, except the one that knows nothing.

All of these beliefs form an incoherent and mysterious network, about which, surprisingly, the average Joe knows very little. Our most important decisions are based on this ‘knowledge’. And yet, most people can’t answer the simplest questions about it!

The purpose of epistemology is to sort this mess out and build our knowledge in a sound and logical way. We will try to understand the nature of knowledge and its underpinnings. We will search a good foundation for our knowledge and the underlying rules for its validity.

To do this, we examine our current knowledge to pick out valid knowledge from invalid one. Using critical thinking, we do a careful filtration of our beliefs, choosing and keeping only the ones we can rely on. Then, we rebuild the rest of knowledge from these solid foundations.

But here, a practical problem faces us. We believe in a incredibly vast amount of things, how could we possibly check them all? The time and work required would be overwhelming. It’s literally impossible to check them one by one.

Descartes quickly realized this and , after some careful thinking, decided to take a radical approach, (?? to do: check if its worth saying this. Can help guide reader into foundationalism and coherentism) which takes its power from the structure of knowledge.

Abandoning all previous knowledge

to do: expand. Theres alot more to say

Because of this limitation, Descartes decides to take a radical stance. Since he cannot check each proposition one by one, he simply abandons all previous knowledge and rebuilds it from the ground up.

This approach is completely opposite to our previous one. He (todo: find better wording) reboots himself and decides to learn, but in a completely logical and rigorous way, creating a strong, trustworthy knowledge.

todo: end product of though. must add reasoning and intuition that lead to it. It is the difference between a good, gnoking textbook and a boring text you want to skip.
Everything he considered to know is now in a I don’t know state. He does not claim them to be false or true. Instead, he leaves all his beliefs behind and reconstructs his knowledge.

His reconstructed knowledge must be based on some basic foundation . It must be an indubitable proposition, whose falsehood would simply be absurd. If there is just the slightest glimpse of doubt, he immediately starts searching for a more solid, more basic proposition.

Level 1: We can’t trust our senses

Imagine you are in a dream. The dream is very realistic, as if you’re were up. This dream dream so real, so perfect to the point where you can’t distinguish it from reality. The voices, the sounds, the personalities are exactly the same. How could you know it was a dream? Because you woke up afterwards.. Otherwise, you had no means of distinguishing this dream from reality.

In this kind of dream, our sensations and feelings, even if they are so convincing, do not correspond to reality. These are false sensations and experiences.

Now, I am going to ask you a question: How do you know you aren’t now in such a dream?

In the Matrix trilogy, everyone lives in a fake world, where what they feel and sense isn’t reality. This allows the machine to control them and get energy from them. (Note: watch the movies, especially the first 2).

How do we know that we aren’t in the Matrix? We don’t know! It is a possibility that we can’t rule out!

Thus, our senses may not be trustworthy. They are not the indubitable, fundamental foundation for knowledge. We experience things, but we have no means to affirms that our experiences correspond to reality.

Reread that. Descartes rejects empiricism. According to him, the senses can not be the foundation of knowledge, since they aren’t trustworthy.

Brain in a vat

Brain in a vat

To illustrate the limitations of our senses, philosophers provide another common analogy. It is the brain in a vat example (à la Matrix).

Imagine the following situation. A mad scientist kidnaps you and removes your brain from your body. He places your brain in a special vat, filled with some strange neurochemical fluid. The scientist connects your brain to a supercomputer. Then, your brain is fed the impulses of a normal day. The brain would feel that the day was like the one before: normal.

Your brain, unaware of its own removal, would believe that everything was normal. It believes it had a normal day, with nothing special. Why would it believe something else?

The experiences of the brain would be identical to the past. Your brain can’t deduce it was tricked. There was no difference. Since your experiences are equal, it is impossible to rule out this possibility.

You may well be currently a brain in a vat … and you would have no means to know it. Your senses may be fooling and tricking you. Your experiences and sensory input would not correspond to reality.

Thus, the brain in a vat is another reason Descartes ruled out the senses as a good foundation for his knowledge.

Level 2: We can’t be sure of the physical world

Everything we know about the physical world comes from the senses. Descartes showed that we cannot rely on our senses. Therefore, we cannot trust anything we knew about the physical world. Our sensations may be completely separated from reality, tricking us.

We may see a bridge, but is there really a bridge? How could we be sure? We could be wrong. In the Matrix Trilogy, people saw, touch, heard things that didn’t exist. Their senses deceived them.

Then, the physical world we live in may be a complete illusion. Some even say that the physical world doesn’t even exist at all.

The physical world is an abstraction we create to make sense of the environment.

Since there is doubt, the existence of the physical world can’t be a good foundation for building knowledge.

Level 3: We can’t be sure of scientific or mathematical knowledge

We continue our quest!

Is Mathematics and Logic the source of all knowledge? Maths seems logical and rigorous, with sound reasoning behind it. There are few things as trustworthy as mathematics and its proofs.

Imagine an all powerful evil demon whose only goal is to fool you. This demon is able to distort your views and opinions. With its incredible powers, it can fool you into believing the most ludicrous statements.

Mathematics and Logic relies on some fundamental axioms. If these axioms are false, mathematics would fall apart. Has the demon tricked us into believing false axioms? Can we be sure that 2 + 2 = 4?

Even if this hypothesis seems far fetched, we cannot reject it. It remains a possibility that we must consider.

Since we cannot be absolutely sure, Mathematics and Logic cannot be our foundation.

Cogito ergo sum

Suddenly, Descartes has a revelation. How obvious!

He can be sure that he thinks. He doubts and thinks. He must exist! How could think without existing? He can be sure he is a thinking thing. His doubts and questions show that he exists.

If he thinks, there is no doubt he exists. How could he think without existing? It’s absurd!

From these 2 statements, we reach Descartes’ foundation: I think, therefore I am. Or, in Latin, cogito ergo sum.

Ironically, doubting your own existence is a very effective way to prove your existence.

(Note: this foundation is the combination of two statements: “I think” and “If I think, I am”.)

Rebuilding knowledge

Starting from cogito ergo sum, Descartes starts building the rest of knowledge.

The approach of building knowledge from some basic foundation is foundationalism. Descartes was the most famous philosopher that used foundationalism. As you can guess, his foundation was cogito ergo sum.

For two different approaches, consult coherentism and infinitism. It’s a very interesting read, if you like epistemology. (Why would you be reading this if you didn’t?)

Hume’s empiricism

David Hume was an important Irish philosopher. He’s notable for his radical ideas on the importance of our sensations and experiences.

He believed that all knowledge is build from sensations and experiences. These impressions leave fainter ideas within us. Every idea comes from the senses. Since ideas form knowledge, all knowledge comes from the senses.

His ideas contrast sharply against Descartes’, which are based on reason, instead of experience.

Ideas and impressions


When we experience an apple, we see its vibrant colors and its round shape, we smell its delicate fragrance and we taste its fruity flavor.

Later on, however, when we think of an apple, we don’t experience all this sensory richness. Instead, we have only a fainter idea of an apple left within us. We have a vague idea of its taste, shape, color and fragrance but it’s less intense.

Similarly, when we think about pain, we don’t experience the actual physical pain. Thankfully, we don’t begin to cry when thinking about sadness and death (or do we?).

In general, our experiences and our ideas are very different. When faced with something, our experiences are what we feel and our ideas are the faint imprint experiences leaves within us.

Ideas are, in some sense, the internal copy we make from our direct experiences. They depend and are created from the impressions, the experiences that we have. All of our ideas come from our experience. Ideas are usually much weaker and fainter than impressions and direct perceptions.

For example, seeing the color red and being angry are impressions while the memory of seeing red and a thougth about anger are ideas.

Since ideas are the imprint of impressions, our ideas are entirely dependent on our experiences. Without experiences, no ideas. This has stupendous implications. It basically states that all knowledge comes from our experiences - empiricism.

As a side note, Hume believes that there are no inate ideas, since we haven’t had any experiences at birth.

Relations between ideas

Relation between ideas

Every idea is comes from our experiences and impressions. However, we can form more complex ideas from simple ones. David Hume identified 4 means to do so:

  1. Conjuntion/Composition: adding ideas together. (e.g. red + bird = red bird)

  2. Transposing: taking an impression and re-arranging its parts (e.g., imagining a person with arms where their legs should be)

  3. Augmentation: making an impression larger (e.g. a whale-sized snail)

  4. Diminution: making an impression smaller (e.g. a snail-sized whale)

Here are some more examples,

  • Hot wine: hot + wine
  • Titan: man augmented
  • God: goodness + wisdom augmented without limit

Why do we care?

Main ideas

These ideas and impressions and relations are very beautiful and all, but why should we care about them? Very simple.

Hume is simply saying that our knowledge is limited by “the materials afforded us by the senses and experience”.

It contrast sharply with Descartes’ rationalism, which aims to rebuild all knowledge through reason.

Hume believes that our experiences, our senses, our cognitive input defines all that we can know. Experience and ideas are the building blocks of knowledge.

Knowledge through the senses

Logic behind empiricism

In short, empiricism states that all knowledge is derived from our senses. Everything we may know is only due to our experiences.

For example, I know there is a table in front of me, because I see, I feel, I sense a table in front of me.

Similarly, I know it’s raining because of the sound and image of the water droplets. I know it through my senses.

However, how do I know that 2 + 2 = 4 through the senses? I can try to add 2 objects to another 2 objects and I get 4 objects. Even if I do this a million times, is this really a proof? How can I be sure that the next time I try I don’t get 5 objects?

Even more complicated, how can I know that torture for the fun of it is wrong through my senses? Are your experiences really a good justification? It seems strange!

There is another problem. People may feel diferently when considering torture for the fun of it (for example)! I might consider it absolutely fine and dandy, while your experience of it is horrendous. Who is right or wrong?

Furthermore, what makes you sure that what you experience will remain constant in time?

For more information, consult the first answer of this Yahoo Answers thread.

The true use of empiricism

Problem of causality

A comic on induction

While Hume was wondering and pondering about these question, he discovered something that blew the view about science apart.

Science is fundamentally based on induction. Every theory and hypothesis is based upon inductive reasoning. From some previous observations, science infers new claims about the future and generalizes. Without it, science could claim very few things (if any).

The classic example is about the Sun. Every morning, the sun rises. Until now, it has constant. Therefore, the sun rises every morning. From past observations, we see a pattern and we generalize.

In science, the fundamental idea is to make some observations and then infer new claims based on them. Science builds universal laws governing every object in the universe. Gravity applies universally to every massful object, independently of time, space and everything else.
Given a cause, science predicts the effects it will have. Give a effect, science will predict what caused it.

Hume completely destroys this principle of causality, this cause-effect reationship, destroying the foundation of science. To understand his argument, we’ll first see an illustrative example:

Every morning, I see the postman at 8 o’clock. Whether it’s sunny, snowing or raining, hot or cold, dark or sunny, he is always there at 8 o’clock. It seems that I can infer that tomorrow the postman will come at 8 o’clock.

Hume claims that even if I see this behaviour 1000 times or a million times, I cannot logically deduce that he will appear at 8 o’clock.

It’s impossible to rule out the possibility that he won’t come. Maybe he will have a car crash. Maybe there will be a bombing at the post office. Maybe the laws of physics will change. There are countless possibilities. The fact that we have seen him acting that way is only a indication that he mioght come, but is not a proof.

Applying this reasoning to science, we see that science will never discover truths, but only theories that are valid until now. A further observation may break a scientific theory.

Science is based on the assumption that the world is uniform and that the laws of nature are constant. However, we have no guarantee that this is true. It may change in the future. Maybe tomorrow, Einstein’s famous equation will be e = m*c^2 + 1. Since Science is based on inductive reasoning, it will never discover thruths, but merely approximations that explain the state of the universe until now.

Rationalism vs Empiricism

Now that we’ve seen a bit better what rationalism and empiricism are, let’s compare them against one another.

What are the weak points and strengths of each position? Can we use a mix of both? How are each used in practical life? Which position is science based upon?

We’ll also try to resume each to its essentials, its gist.

Rationalism in a nutshell

Descartes’ rationalism is quite simple. Simplifying, it consists of 3 simple steps:

  1. Abandon all previous knowledge
  2. Find a solid foundation
  3. Rebuild knowledge from foundation through reason

Descartes concluded that the senses could not be a foundation, using his examples:

  • Evil demon
  • Brain in a vat
  • Perfect dream

Instead, he relies on cogito ergo sum to rebuild knowledge. Descartes considers this a true, self-evident indubitable sentence. Even if he’s subject to his examples, he has no doubt that this remains true.

Empiricism in a nutshell

Empiricism states that all knowledge comes from experience and the senses.

We can be certain that have experiences and sensory input. Our knowledge and ideas will be due to our experiences.

Empiricists claim that reason can only create relation between ideas, but is unable to find a indubitable foundation from which knowledge emerges. Rationalists need to have some a priori facts to rebuild their knowledge. Whether such innate knowledge exists or not is uncertain.

However, we can be sure that we sense and experience things. These experiences are the true beginning and source of knowledge; the true indubitable foundations of knowledge.

Rationalist argue that our experiences may not correspond to reality, but they are the starting point/foundation from which all knowledge stems.

Rationalism’s strengths

Empiricism’s strengths

Final comments

Kant ???

Does science provide knowledge ?

Since we’re talking about knowledge, we must talk about science. It’s one of the most serious advances in humankind’s intellectual’s history.

We use it constantly, but does it really give knowledge? Are there limitations to the power of science? What is the difference between a ‘scientific’ and a ‘non-scientific’ theory?

Knowledge and science

Does science bring knowledge? How?

These are the question we will first try to answer in this section. We will examine various points of view. We will analyse some of the work by the most important philosophers in this area, such as Karl Popper.

Let’s begin!

Answer 1: Knowledge through induction

Induction states that we can predict what will happen in the future from what we lived until now. For example, all dogs we saw until now bark. Therefore, all dogs bark.

This position assumes that nature is uniform. In other words, nature acts the same way in the future as it did until now.

But is Nature uniform? To know this, we must observe all events and things, in the past and in the future. Since this is clearly impossible, there is still the logical possibility that Nature is not uniform. (e.g. We might see a dog purring)

This is the major problem with induction. Since we can’t exclude the possibility that Nature is not uniform, our theories will be guesses, with a high or low probability of being correct.

They do not provide knowledge. We can’t be sure that they are right. Therefore, induction is not a path to knowledge.

Answer 2: The scientific method

This method consists of 4 steps:

  1. We form an hypothesis
  2. We deduce some possible consequences
  3. We experiment
  4. We modify the theory or find a new one, if necessary

Why is this method any good? To see we, we will resort to Karl Popper, one of the greatest philosophers of science.

Karl Popper and falsifiability

For Karl Popper, one essential characteristic science theories must have is falsifiability. A theory is scientific if it can refuted through some appropriate observation. If a theory, even when faced with contradictory evidence, is not refuted, then it is not a scientific theory. Science is evidence-based.

All swans are white.

This theory is falsifiable, since seeing a black swan would show it to be false. It is possible to refute the theory, if we saw some blue or orange swan.

What makes a theory scientific?

According to Popper, his refutability / falsifiability criterion is the key to distinguish scientific theories from non-scientific theories. A theory is scientific if and only if some observation can show it to be false.

You go to an astrologer.

Astrologer: - Your favourite color is blue.
You: - No, it’s green.
Astrologer: - I must check your sign and the constellations on the day of birth. Let me restart.

Was he being scientific? No! When a critical error in his theory was found, he refused to abandon it and instead tried to explain it via some other astrological phenomenon.

What makes a scientific theory better than another ?

If both theories are falsifiable, then there are some observations which would refute them.

First, no such contradictory observations must have been made, because otherwise these theories are simply wrong.

I will give you two theories. Which theory is better in your opinion?

  1. All animals evolved.
  2. Cows evolved.

It’s the first one. It is more general, more abstract. It is also more risky, since there are much more observations that would invalidate it.

The riskier a theory is and the more observations can be made to disprove it, the stronger it is. Why?

Because despite being so risky, no exceptions to the rule were found. Then, both are as acceptable, but the first explains a much wider variety of things. Therefore, it is a better theory.

Progress in science is simply the strengthening of our current scientific theories. When discovering a stronger theory, progress has been made.

Why is falsifiability / refutability important?

According to Popper, science’s goal is to discover and approach the truth. By elaborating new and more general theories, we get each time a little closer to the truth.

The stronger a theory is (and if its still standing against experiment), the better it is. It’s riskier, more general and abstract. It has a greater explanatory potential, since it can explain a wider variety of phenomenon than the previous theory. Yet, it has survived all attempts to falsify it. The new theory is better than the previous one.

Through falsifiability, we can find which theories are better. It allows us to see science’s progress, by each time approaching the truth a little more, thanks to our better theories.

Of course, it’s impossible to know if a theory is the truth, because there may always exist an experiment which would invalidate it (since it is falsifiable).

It is impossible to know if such an observation, if such an experiment will happen in the future. Why? Because we can’t prove that nature is uniform: the induction problem.

Even if we approach each time a bit more, but the truth will always be an ideal.

The scientific method is practical falsifiability

Scientific method

The scientific is simply a method that respects Popper’s falsifiability criterion.

To explain a phenomenon, it formulates hypothesis and tests them. If a theory has explanatory power and can survive all the tests, we consider it temporarily valid.

A simple contradictory observation takes us back to square 1. We make a new theory and test it until we have found a satisfactory one.

What does this method product? A refutable tested scientific theory! Popper’s dream! This is why this method is so fundamental in science.

The scientific method respects the falsifiability criterion. It is useful, logical and results in tested refutable theories!

Are there limitations to our knowledge?

Lot of ideas

Must connect them

Form relation

Contrast between three theories f knowledge

Build relations with S knows P, justification science

and limits to our knowledge

Structure of knowledge

infinite regress

foundationalism network arising from some axioms

coherentism where knowledge arises from a coherent network of statements

Problems of each:
foundationalism: arbitrariness in choosing axioms
coherentism: possibility of existence of various coherent networks, but uncoherent with one another
e.g. one network states P and another one states (not P)

see skepticism for acceptance of this

note: say something about infinitism

must present graphs to gnok the subject easier
search or create, by facility and availability