Lecture 5 Flashcards
What is Cogency?
An argument is cogent if and only if it is not valid, but if all the
premises are true, the conclusion is probably true
Otherwise, the argument is non-cogent.
Example of cogent argument
- Quitting smoking tends to improve one’s health.
- Mary has quit smoking.
Therefore, probably, her health will improve
What is a Non-Cogent Argument?
possible but not likley
does a cogent argument have to be true?
a cogent argument doesn’t have to have a true premises, and it doesn’t have to have true conclusions either: what’s important is the relation between premise and conclusion.
What is an example of a cogent argument
- Most chairs have ten legs.
- Prime Minister Justin Trudeau is a chair.
therefore, probably Trudeau has 10 legs.
This argument has two false premises and a false conclusion … but,
nevertheless, it’s what we call cogent.
Why?
if the premises were true, the conclusion would be probable.
What is the cogency test?
**Imagine/suppose that the premises are all true. Assuming this, is the
conclusion likely to be true as well?
If the answer is “yes”, then the argument is cogent
If the answer is “no”, then the argument is non-cogent
A Cogent Argument Can Have
- all true premises, true conclusion
- all true premises, false conclusion
- one or more false premises, true conclusion
- one or more false premises, false conclusion
When testing for cogency what is main issue?
it’s whether the premises, if all true, would make the conclusion probable.
1 cogent Argument Pattern
- Most A’s are B’s
- X is an A
- therefore, probably, X is a B
- Most profs have PHD
- Kraay is prof
- therefore Kraay has a PHD
Another cogent argument pattern
- X is an A
- X is a B
- Most AB’s are C’s
therefore X is a C - Kraay is right handed
- Kraay is a professor
- Most right handed profs are nice
therefore, it’s likely that kraay is nice
Some common patterns of Non-Cogent Argument?
- Most A’s are B’s
- X is not A
- X is not B
Most professors have PhD’s
Zola has a PhD
Therefore, probably, Zola is a professor
What is validity like?
Validity is like an On- Off switch.
What is cogency like?
just like a dimmer.
What is deductive strength?
a) Valid,
b) rational/ justified/ reasonable for the person to beleive that all of the argument’s premises are true, based on the available evidence.
How can a deductive argument be weak?
a) invalid
b) not rational/ justified
c) both a+b
Can a valid argument be strong? weak?
yes
Can a strong argument can’t be invalid?
no. a strong argument by definition is valid.
What is inductive strength?
- An argument is inductivley strong…
- cogent
- rational resonable/ justified
- not defeated by a person’s total evidence
Can a cogent argument be strong? weak?
yes.
Can an inductively strong argument be cogent?
by def it must be strong. And can’t be weak.
If a argument passes the first step of cogency test, but it’s not true. is the argument strong?
no, because it’s not reasonable
can we measure cogency?
yes, cogency comes in degrees. The more reasonable something is, the more likely it is to happen.
Someone coming walking in with new evidence in court to make a suspect inocent is an example of?
being defeated by a person’s total evidence
An inductive argument has to be
probable