PHILOS 2CT3 Chapter Notes - Chapter 3: False Premise, Sentence Clause Structure, Deductive Reasoning

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8 Feb 2016
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Philo 2CT3
Chapter Three
- Resumption of what was dealt with in Chapter One
Argument Basics
- The point of devising an argument is to try and show that a statement/claim is worthy of
acceptance
- The point of evaluating an argument is to see whether or not the task has been successful
- If the argument is worthy of acceptance it’s a “good” argument and if it isn’t it’s
considered a “bad” argument
- DEDUCTIVE ARGUMENT: an argument intended to provide logically conclusive
support for its conclusion
- INDUCTIVE ARGUMENT: an argument in which the premises are intended to provide
probable, not conclusive, support for its conclusion
- A deductive argument is thought to be either valid or invalid
VALID ARGUMENT: a deductive argument that succeeds in providing
conclusive support for its conclusion
If its premises are true, the conclusion must be true
INVALID ARGUMENT: a deductive argument that fails to provide conclusive
support for its conclusion
- A valid argument doesn’t need to be true
“Logical structure” doesn’t refer to the content of an argument but to its
construction – the way the conclusion and the premises fit together
- TRUTH-PRESERVING: a characteristic of a valid deductive argument in which the
logical structure guarantees the truth of the conclusion if the premises are true
You may or may not agree with the premises, but it’s impossible for the premises
to be true and the conclusion false
- Even an argument with a conclusion that is obviously true can be invalid if that
conclusion isn’t supported by the premises
- An inductive argument is thought to be either strong or weak
STRONG ARGUMENT: an inductive argument that succeeds in providing
probable – but not conclusive – support for its conclusion
If its premises are true, its conclusion is probably/likely to be true
WEAK ARGUMENT: an inductive argument that fails to provide strong support
for its conclusion
- Because the truth of the conclusion can’t be guaranteed by the truth of the premises,
inductive arguments aren’t truth-preserving
- A good argument is one that has proper structure and true premises
- SOUND ARGUMENT: a deductively valid argument that has true premises
A good argument that gives you good reason for accepting its conclusion
- Three different types of deductive arguments
False premises, false conclusion
False premises, true conclusion
True premises, true conclusion
- A good inductive argument must also have true premises
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Can be inductively strong with a false premise but that doesn’t make it a good
argument
- COGENT ARGUMENT: a strong inductive argument with all true premises
- The kind of support a deductive argument gives a conclusion is absolute while the
strength of an inductive argument can vary from weak to strong
Judging Arguments
- Questions to answer:
1. How can you tell whether it’s deductive or inductive?
2. How can you determine whether it gives you good reasons for accepting the conclusion
(whether it’s sound or cogent)?
- Step 1: Find the conclusion and then the premises
- Step 2: Ask “Is it the case that if the premises are true the conclusion must be true”?
If yes = deductive
Then find out if it’s sound
If no = move on to the next step
- Step 3: Ask “Is it the case that if the premises are true its conclusion is probably true”?
If yes = inductive
Then check to see if it’s cogent
If no = move on to the next step
- Step 4: Ask “Is the argument intended to offer conclusive or probable support for its
conclusion but fouls to do so”?
If you’ve reached this step you’ve already eliminated 2 possibilities: a valid
argument and a strong one
You must now figure out what type of (failed) arguments is intended
Guideline 1
- Generally, if an argument looks deductive or inductive because of its form, assume that
it’s intended to be so
- Words that tend to signal a deductive argument include: it necessarily follows that/
absolutely/ necessarily/ certainly
- Words that tend to signal inductive arguments include: likely/ chances are/ odds are/ it’s
plausible that
- The only remaining task is to figure out whether the argument is invalid or weak
Finding Missing Parts
- Implicit premises or assumptions are vital to an argument
- Some conclusions are linked to certain premises only if we assume an additional premise
- 3 step process for the investigation of implicit premises
- Step 1: search for a credible premise that would make the argument valid, one that would
furnish the needed link between premise(s) and conclusion
Choose the supplied premise that (a) is most plausible, and (b) fits best with the
authors intent
(a) looks for premises that are either true or not obviously false
(b) means premises should fit – or at least not conflict – with what seems
to be the authors point/purpose
These 2 requirements embody “the Principle of Charity in Interpretation”
or just “the Principle of Charity”
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