PHL232H1 Lecture Notes - Lecture 2: Basic Belief, Indicative Conditional, Material Conditional
2016-09-14
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PHL232 Lecture 2
The Sceptical Challenge
- An arguments for scpeticism from a sceptical hypothesis
• P1. I know that: If I am in a philosophy lecture, then I am not a brain in a vat.
(knowledge based on a conditional truth)
• P2. If P1 is true, then: if I know that I am in a philosophy lecture, then I also know
that I am not a brain in a vat.
- These two premises jointly lead to the intermediary sub-conclusion
• C1. Therefore: If i know that I am in a philosophy lecture, then I also know that I am
not a brain in a vat. (P1, P2)
• P3: I do not know that I am not a brain in a vat.
• C2: Therefore: I do not know that I am in a philosophy lecture
- This is a basic argument for scepticism from a sceptical hypothesis about the
external world.
- Why is this a valid argument?
Validity and Soundness
- They are both properties that apply to deductive arguments as a whole, not properties
that apply to individual statements, propositions, etc.
- Validity is the property of an argument when the premises lead to the conclusion.
Support, imply or entail the argument’s conclusion.
• An argument is valid if and only if there is no possible way that the premises could
be true and the argument’s conclusion false. Otherwise, an arguments is valid if
and only if necessarily if the arguments premises are true so is its conclusion.
- An argument is sound if and only if it is a valid argument AND it has true premises.
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2016-09-14
2
Knowledge as Justified True Belief
- Historically, attempts to respond to the sceptical challenge took place against the
backdrop of the view that knowing a given proposition involved having a justified true
belief in that proposition.
- This view is sometimes referred to as the tripartite analysis of knowledge.
- It is also sometimes referred to as the JTB analysis of knowledge.
• In order for Subject S to know some Proposition P it is both necessary and
sufficient that the subject follow the three following conditions:
- S believes that P
- S’s belief that P is justified
- P is true.
• Intuitively, knowledge implies truth.
• Knowledge also implies belief. It is difficult to see how you could know
something and yet not believe it.
- Necessary and Sufficient Conditions
• A is sufficient for B: this means that the obtaining or occurring of A is enough to
bring about the obtaining or occurring of B.
• A is necessary for B: this means that B could not obtain or occur without A’s
obtaining or occurring
- Applying the Distinction
• If I were a brain in a vat, it would still seem to me as though I were in a philosophy
lecture, given my perceptual experience.
• It would SEEM that I am perceiving the exact same things.
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Document Summary
An arguments for scpeticism from a sceptical hypothesis: p1. I know that: if i am in a philosophy lecture, then i am not a brain in a vat. (knowledge based on a conditional truth: p2. If p1 is true, then: if i know that i am in a philosophy lecture, then i also know that i am not a brain in a vat. These two premises jointly lead to the intermediary sub-conclusion: c1. This is a basic argument for scepticism from a sceptical hypothesis about the external world. They are both properties that apply to deductive arguments as a whole, not properties that apply to individual statements, propositions, etc. Validity is the property of an argument when the premises lead to the conclusion. Support, imply or entail the argument"s conclusion: an argument is valid if and only if there is no possible way that the premises could be true and the argument"s conclusion false.
