'Introduction to Deductive Reasoning' by Leonard Peikoff

Introduction to Logic by Leonard Peikoff -- part 4: Introduction to Deductive Reasoning

This lesson covers the nature of deductive argument, including: validity and truth; mixed and pure hypothetical arguments; and alternative arguments.

Recorded in 1974.

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[gykyqew]

12:54 rules of validity of deductive argument
1)if something then something 16:00
2)either something or something
3)a straightforward categorical assertion with no if then and no either or
"Categorical statements "
22:08 standard form
Any one of them is valid they are all valid
Purpose of symbolize is verify validity of structure
28:30 number 1 affirming the antecedent is valid
Valid meaning conclusion follows
29:35 number 2 denying the antecedent is invalid
Fallacy of denying antecedent
Does not say only if
Statement P implies Q gives you only sufficient condition of Q
It says p is enough to produce Q
If you have P you will get Q but it doesn't tell you that P is necessary to get Q
It doesn't say you Have to have P to get Q
This type of reasoning is invalid
36:00 number 3
Maybe something else other than P produce Q
37:45 number 4
44:50 mean that but they don't literally say it
Only if P then Q reverse of if then statement
If then statement gives sufficient condition
Only if Statement gives necessary condition but it may not be sufficient
47:02 two different choices
1》drop only and negate both constituents
Only p implies Q - P prime implies Q Prime
2》drop only and reverse constituents
P implies Q
50:58 synonym of if (english)-conditional idea
when, where, provided that, condition that, assuming that
substitute if
When men think then they prosper
Ordinary language 》reverse of one thing depending on another
He will pass if you motivated
Standard form: if you motivated then he will pass
52:25 unless =if not
Unless you study you fail
If you do not study you fail

[gykyqew]

54:00 logical indicator (english)
》Conclusion Introduction by therefore, as, so, as a result, I conclude, hence, consequently, thus
》Premise introduction by for, because, since, on the grounds that, on the premise that, my reason is
59:00 pure hypotheticals
valid chain
1:04:25 rules of valid chain (sororities)
Broken chain is invalid pure hypotheticals
1:10:54 1》premises may not have been presented in the right order
2》look for only's(two choices)
Get ride of only
3》 general principle 》rewrite a statement
P implies Q us identical to Q prime implies P Prime (reverse and negate)
Number 5
1:22:02 alternative arguments
1:27:20 separate rules if validity for weak alternation
Number 6 is invalid
One alternate, another alternate
》Premise tell you one or other maybe both but atleast one must be true
》P2 maybe both true or maybe both not true
Second premise tell you one alternate true we can't conclude anything about the other one
1:33:13 rule dictate weak alternation
Fallacy of weak alternation
1:35:25strong alternation
Either P or Q or not both one must be true at minimum one can be true at maximum
Weak tells you if either is false the other is true but weak doesn't tell you if either is true the other must be false it leaves open maybe both
1:40:50 transform alternate to hypothetical P v Q rewritten as
P prime implies Q
Alternation to implication and negate the first
1:45:05 informal fallacy 15Q
2:01:30 informal fallacies 45Q

[setemendigos]

1:43:00 Complementing: composition finds the possible generalizations between the elements of a set. Integration finds the relationships that exist between these elements and that are not contradictory.