Summary
Summary PHI1025F Test 2 Preparatory Notes
- Course
- PHI1025F Critical Thinking
- Institution
- University Of Cape Town (UCT)
This is a comprehensive and detailed preparatory note for test 2. Essential!!
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● If [sufficient condition], then [necessaryRecap condition].
Valid Argument - if we assume the premises are Antecedent - “sufficient condition”; it is enough to
true, then the conclusion has to be true. bring about the consequent.
We use the 3 valid argument forms (Modus Ponens, Consequent - “necessary condition”; it MUST
Modus Tollens, or Eliminative Syllogism) to assess occur if the antecedent occurs.
validity. “Only If” - a necessary condition
Modus Ponens ● “Only if” is not the same as “if”.
1. If P, then Q. ● After “only if” is the consequent.
2. P. ● Remove “only if” when re-writing the
3. So, Q. conditional.
Modus Tollens “Must” - a necessary condition
1. If P, then Q. 1. If M, then not-F. ● What “must be done” is the consequent.
2. Not-Q. 2. F. “Required” - a necessary condition
3. So, not P. 3. So, not-M.
● What is “required” to occur is the
1. If M, then F. consequent.
2. Not-not F.
“Necessary For” - a necessary condition
3. So, not-not M.
● What is “necessary for” is the consequent.
Eliminative Syllogism / Disjunctive Syllogism
“Sufficient For” - sufficient condition
● There are no conditionals in eliminative
syllogisms, there are disjuncts which make ● What is “sufficient for” is the antecedent.
up a disjunction. “Sufficient Condition” - sufficient condition
● Disjunctions are “Either P or Q.” claims. ● The “sufficient condition” is the antecedent.
● P and Q are disjuncts. “Unless”
● A disjunction is true if at least 1 of the ● When re-writing the conditional, replace
disjuncts is true. “unless” with “if … not [antecedent], then
(not) [consequent]”.
1. Either P or Q. 1. Either P or Q.
2. Not-Q. 2. Not-P. Informal Fallacies
3. So, P. 3. So, Q.
● Fallacy - is an error in reasoning.
Good Deductive Arguments - are valid and sound.
● Fallacious Argument - the premises do not
Soundness - an argument that is valid with all true support the truth of the conclusion.
premises and a true conclusion.
● Informal Fallacies - are defective arguments
Unsoundness - an argument that is invalid with at due to the content of the premises, but are
least 1 true premise. not necessarily invalid.
Conditionals Informal Fallacies of Evidence
● If [antecedent], the [consequent].
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