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5.2: How Do We Know What We Know?

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    Types of Knowledge

    Although philosophers may differ on how many different types of knowledge there are, they agree with Propositional Knowledge, the claim to have knowledge of different things. What they may have in common, what makes them knowledge, then becomes the issue.

    Here is one schema for different types of propositional knowledge.

    • Logical
    • Semantic
    • Systemic
    • Empirical

    What are these about? Why make these distinctions?

    Consider that you probably would claim to know the following things.

    1. There are three sides to a triangle. The sum of their angles is 180 degrees.
    2. There is a computer in front of you right now.
    3. 23 + 11= 34
    4. A bachelor is an unmarried male.
    5. If a is more than b, and b is more than c, then a is more than c.

    These sentences all make claims that can be determined to be either true or false. They are sentences that express propositions. They are claims about which you can come to a judgment as to whether or not they are true. You probably know that they are true. Now how is it that you come to know these things? Obviously, you come by this knowledge in different ways. This relates to the idea of the different types of knowledge.

    Logical Way of Knowing

    There is a knowledge that is the result of the understanding of the relationship of ideas to one another. There are the rules or laws of logic that permit claims to knowledge that are further statements of ideas consistent with the rules and the ideas already accepted.

    Here is another example where you do not need to know what I am talking about because you know the relationships involved.

    1. All gazintz are gazatz
    2. All gazatz are garingers
    3. Therfore, all gazintz are garingers.

    You can claim to know that: if a and b are true, then c is true as well. This you know by logic.

    Semantic Way of Knowing

    There is knowledge that is the result of learning the meaning of words. Knowledge of words is knowledge of definitions. Such definitions are set in dictionaries. So bachelors are unmarried males. You know this. People acknowledge this. Are newborn baby boys bachelors? Do people say to the new mother in the hospital nursery: "Oh what a beautiful bachelor you have there Ms. Jones!”?

    Systemic Way of Knowing

    There is knowledge of mathematics and geometry, which is the result of learning a system of words, or symbols and how they relate to one another and the rules of operating in that system and then any claims made that are consistent with those definitions and rules is called knowledge.

    Empirical Way of Knowing

    There is a knowledge that comes through our senses. This knowledge is empirical knowledge. Science is the best example of a method for ascertaining the accuracy of such knowledge. Scientific knowledge is a result of the practice of the method: observation, abduction of a hypothesis, careful observation, refinement of hypothesis, deduction of test for hypothesis, testing and experimentation, confirmation or falsification of the hypothesis.

    What do these four types of knowledge have in common? One of the most popular theories of knowledge of the 20th Century holds that knowledge does imply a belief.

    Belief does not imply knowledge. Wherever people claim to know that something is true they believe that it is so. When people claim to believe that something is so they don’t always claim to know that it is so.

    What kind of a belief is knowledge.?

    To begin with it must be true. You cannot know something that is false.

    It must be true and you must claim to know it and it be true not by accident or coincidence but because there is evidence to support and enough to warrant or justify the claim to know.

    • So, knowledge = justified true belief
    • Evidence is needed for justification

    Edmund Gettier's Justified True Belief

    Warranted true belief may not be knowledge if true by accident.


    On January 1, 2001 the claim is made: I know that the Giants are going to win the Super Bowl in 2001. It turns out that several weeks later they did win. Can I claim that I knew it on January 1st or was it just a lucky guess or a well-informed guess? How does a person gain the warrant or the justification for the belief? Well, depending on the type of belief that it is there are different kinds of warrants.

    Modes of Warranty

    • Logical warrants are found in the rules of logic. Follow them and the claim is warranted.
    • Semantic warrants are found in the dictionaries. Use them, be consistent with them and the claim is warranted.
    • Systemic warrants are found within the system (math or geometry) follow the rules be consistent with the definitions and rules and the claim is warranted.
    • Empirical warrants are found with evidence. How is the evidence to be gathered, examined and evaluated?

    There are four types of beliefs when considering truth and warrants:

    1. Warranted true beliefs: this type is called knowledge
    2. Warranted false beliefs: this type cannot exist at all.
    3. Unwarranted true beliefs: these are lucky guesses or coincidences and not knowledge.
    4. Unwarranted false beliefs: these are just wild unsupported claims or wishes that are not true .

    Why knowledge is justified true belief

    Justification warranty comes in degrees. How much evidence is needed in order to determine whether or not someone knows something or not? How much evidence is needed in order to determine whether or not someone has sufficient warrant to make a claim to know something or not? How much is needed depends on what is riding on the outcome of the claim. For simple matters of little consequence humans appear to accept fairly small amounts of evidence. For important matters much more evidence is needed.


    How old is someone? If someone claims to know how old John Smith or Mary Doe is we probably accept the claim on their word if it is just gossip. However, if there were a $10 bet on it we would ask for evidence. We might go to the person and ask them to confirm the claim. If it were $100 we might want a driver’s license. If it were $1000 we might want a birth certificate. For $10, 000 we might want to go to the official registry and check the official documents ourselves.

    The highest consequences on claims to know: human life. At a criminal trial, a capital homicide case, what is the standard of proof? It is evidence that is convincing beyond a reasonable doubt. Not beyond all doubts. But beyond reasonable doubts, meaning beyond all doubting or questioning of the evidence that we have reason to doubt or question.

    Scientists have their reputation riding on their claims to know things. The standard for the warrant in science is that their claims be supported by evidence that other scientists can examine, experiments that others can repeat and get the same result and equations that others can examine to check against errors.

    So, claims to know may be accepted depending on amounts of support that may vary in the type and amount depending on the type of claim that it is. However, to know something that which you claim to know must be true and truth does not have degrees: because a statement P is either true or it isn't.


    Philosophical Application

    Suppose your friend claims to have answered a philosophical question. In listening to her answer, you are struck by how rational she is. She has followed the laws of thought (she doesn't contradict herself), she has made the fewest assumptions possible while giving a complete explanation (Ockham's Razor), and she is able to give complete answers to any of your questions (the principle of sufficient reason).

    Is this enough to convince you that her answer is correct, or is it always possible to doubt the use of reasoning itself? Explain.

    What more would you need to believe her and why?


    Vocabulary Quizlet 5.2

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