Lecture Five Chapter 3 & 4
Inductive arguments; try to show that the conclusion is guaranteed and certain.
Premises are intended to give probable, not conclusive support for the conclusion.
The difference between inductive and deductive arguments is that inductive says that
the conclusion will be certain however deductive says that it might be true.
Inductive: HAVE to be true
Deductive: might be true
COGENT ARGUMENT:
Cogency: an argument is cogent if and only if it is not valid, but the premises of the
argument are good reasons for the conclusion.
For an argument to be cogent:
- Argument has to be not valid
- If all the premises are true, then the conclusion is PROBABLY true
If it doesn't make the condition, the argument is non-cogent.
Example:
Cogent Argument:
1. Quitting smoking tends to improve one’s health.
2. Mary has quit smoking.
Therefore, probably
3. Mary’s health will improve.
This argument is cogent because the premises are right and the conclusion is probably
true however its NOT valid because the conclusion is NOT CERTAIN for sure true.
Non-Cogent Argument:
1. A few police officers are corrupt.
2. Jim is a police officer.
Therefore, probably
3. Jim is corrupt.
,This argument is not valid because the premises being true does not make the
conclusion GUARANTEED to be true, it is also non-cogent because the conclusion is
not likely.
Note: A cogent argument doesn't have to have true premises, and it doesn't have to
have true conclusions either: what's important is the LOGICAL RELATIONSHIP
between the premises and conclusions.
Example of Cogency:
1. Most chairs have ten legs.
2. Prime minister Justin Trudeau is a chair.
Therefore, probably
3. Prime Minister Justin Trudeau has ten legs.
This argument has
- 2 false premises
- False conclusion
That's WHAT MAKES IT COGENT.
THE COGENCY TEST:
Imagine that the premises are all true. Does this make the conclusion LIKELY to be true
as well?
- If yes, then the argument is COGENT.
- If no, then the argument is NON-COGENT.
A cogent argument can have: (find examples)
- All true premises, true conclusion
- All true premises, false conclusion
- One or more false premises, true conclusion
- One or more false premises, false conclusion
Testing for cogency is not about whether the premises and conclusion are actually true,
it is about whether the premises, if all true, would make the conclusion PROBABLY true.
, THE COMMON PATTERNS OF COGENT ARGUMENTS:
Argument pattern and example beside: (cogent arguments)
My own example:
1. Most doctors have doctorates.
2. I am a doctor.
Therefore, PROBABLY
3. I have a doctorate.
NON-COGENT Arguments:
1. Most As are Bs.
2. X is not an A
Therefore, probably
3. x is not a B.
Example of this:
1. Most professors have PhDs.
2. Zola is not a professor.
Therefore, probably
Inductive arguments; try to show that the conclusion is guaranteed and certain.
Premises are intended to give probable, not conclusive support for the conclusion.
The difference between inductive and deductive arguments is that inductive says that
the conclusion will be certain however deductive says that it might be true.
Inductive: HAVE to be true
Deductive: might be true
COGENT ARGUMENT:
Cogency: an argument is cogent if and only if it is not valid, but the premises of the
argument are good reasons for the conclusion.
For an argument to be cogent:
- Argument has to be not valid
- If all the premises are true, then the conclusion is PROBABLY true
If it doesn't make the condition, the argument is non-cogent.
Example:
Cogent Argument:
1. Quitting smoking tends to improve one’s health.
2. Mary has quit smoking.
Therefore, probably
3. Mary’s health will improve.
This argument is cogent because the premises are right and the conclusion is probably
true however its NOT valid because the conclusion is NOT CERTAIN for sure true.
Non-Cogent Argument:
1. A few police officers are corrupt.
2. Jim is a police officer.
Therefore, probably
3. Jim is corrupt.
,This argument is not valid because the premises being true does not make the
conclusion GUARANTEED to be true, it is also non-cogent because the conclusion is
not likely.
Note: A cogent argument doesn't have to have true premises, and it doesn't have to
have true conclusions either: what's important is the LOGICAL RELATIONSHIP
between the premises and conclusions.
Example of Cogency:
1. Most chairs have ten legs.
2. Prime minister Justin Trudeau is a chair.
Therefore, probably
3. Prime Minister Justin Trudeau has ten legs.
This argument has
- 2 false premises
- False conclusion
That's WHAT MAKES IT COGENT.
THE COGENCY TEST:
Imagine that the premises are all true. Does this make the conclusion LIKELY to be true
as well?
- If yes, then the argument is COGENT.
- If no, then the argument is NON-COGENT.
A cogent argument can have: (find examples)
- All true premises, true conclusion
- All true premises, false conclusion
- One or more false premises, true conclusion
- One or more false premises, false conclusion
Testing for cogency is not about whether the premises and conclusion are actually true,
it is about whether the premises, if all true, would make the conclusion PROBABLY true.
, THE COMMON PATTERNS OF COGENT ARGUMENTS:
Argument pattern and example beside: (cogent arguments)
My own example:
1. Most doctors have doctorates.
2. I am a doctor.
Therefore, PROBABLY
3. I have a doctorate.
NON-COGENT Arguments:
1. Most As are Bs.
2. X is not an A
Therefore, probably
3. x is not a B.
Example of this:
1. Most professors have PhDs.
2. Zola is not a professor.
Therefore, probably
