Critical Thinking
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Transcript of Critical Thinking
Cri$cal Thinking ARGUMENTATION FOR THINKING AND REASONING
Dr. Donald N. Philip
"[Logic] took the mys$c fog from your head and gave you a mind like a knife." (Burke, nd, ≈29:09 et seq.) Reference: Burke, J. (Writer). (nd). In light of the above: Medieval conflict, faith and reason (Ep. 2) [Video], The day the universe changed.
Argumenta$on • The topic of cri$cal thinking is inextricably entwined with the topic of
argumenta$on (defined as "... the ac$on or process of reasoning systema$cally in support of an idea, ac$on, or theory"). When you engage in cri$cal thinking, you are engaging in an evalua$on of the argumenta$on used by someone to make a point, which is why they are entwined–the one cannot exist without the other.
(Not this kind of argument though.)
Syllogis$c logic • Logic is the philosophic study of reasoning to dis$nguish between reasoning that
is true (valid) and reasoning that is false (invalid).
• One of the main logical forms is the syllogism, which arose in about the 5th C BCE in Hellenis$c Greece, and which is closely associated with Aristotle.
• Formal syllogis$c form: 1. Major premise (general): All mammals are warm-‐blooded. 2. Minor premise (specific): My cat is a mammal. 3. Conclusion: Therefore my cat is warm-‐blooded.
• Note that there has to be a connec5on between 1 and 2 for 3 to be valid. In this case it is the word “mammal.” As well, we can see that the conclusion contains new knowledge that cannot be deduced from either premise by itself.
• Syllogisms are ogen informal in common speech or wri$ng, but ogen we can put this into syllogis$c form to analyze the chain of reasoning.
Using Venn Diagrams
As in the previous example, Venn diagrams are useful in illustra$ng syllogisms. In the example here, we could create:
1. All people are mortal. 2. Women are people. 3. Therefore all women are mortal.
The syllogism is valid, but we haven’t included men because we said nothing at all about men … but we could if we wanted to using the informa$on in this diagram.
Invalid Syllogisms • Syllogisms only work if the major premise and minor premise are:
• Both true and verifiable, and
• There is a connec$on between them.
• Ogen there is a problem, as one of the premises is not verifiable, or the connec$on is implied but absent. In either case, we would reject the syllogism.
Statements can be true, but …
In this case, both the major premise (corn is a vegetable) and the minor premise (chickens have feathers) are true. Also chickens do eat corn. The problem is that there is no connec$on between the major and minor premise and therefore no conclusion can be made based on the given evidence. The syllogism is invalid and we would reject it.
Major Premise Minor Premise
Real life example …
• Source: Quantum Memoryhlp://www.crystalhealinglight.co.uk/Quantum_Memory.html
1. “Quantum memory is received by the present self from overlapping wave func$ons across $me and space.”
2. “As all $me exists simultaneously, memories from our past and future selves are con$nually crea$ng new palerns and wave forms”
3. Therefore, “New quantum selves are created as the waves overlap and new aspects of our personality are woven in the present now.”
• Is this a valid or invalid syllogism, and why?
• Note that one trick that is ogen used to imply a connec$on between two statements (paragraphs usually) by juxtaposing them together. Then a third paragraph makes a conclusion based on the implied connec$on. If the ¶s are long enough, this can seem en$rely reasonable.
Limita$ons of syllogisms … • There are limits to the power of syllogis$c logic. If you start with things that you
think are true, but aren’t, then you can form syllogis$cally valid conclusions but that simply aren’t true. For example, using the Aristotelean theory of elements (Earth, Air, Fire and Water) …
1. Things that burn contain the element Fire. 2. Coal is a mineral that burns. 3. Therefore coal contains Fire.
• This is a valid syllogism that isn’t true because we now know that Fire isn’t one of the elements.
• This is one of the reasons why Francis Bacon (17th C philosopher) rejected the syllogism in favour of observa$on and experimenta$on.
• However syllogisms are s$ll very useful when we have solid knowledge about the things the syllogism discusses.
Summing up … • This has been an all-‐too-‐brief explora$on of syllogis$c logic. Syllogisms are
useful, but have their limita$ons. One of the chief ways syllogisms can be useful is in analyzing ar$cles and papers for the soundness of their argumenta$on. Ideally, you should be able to iden$fy the statements in the ar$cle and put them into syllogis$c form. If the syllogisms hold true, then the argumenta$on is good. However if the syllogisms are lacking somehow, then either something important has been leg out, or the syllogisms is just plain wrong. In either case we would reject the arguments.
• The Wikipedia ar$cle on syllogisms is quite good and illustrates the various fallacies one finds in syllogisms. See hlp://en.wikipedia.org/wiki/Syllogism
• James Burke’s “In light of the above: Medieval conflict, faith and reason (Ep. 2)”, The Day the Universe Changed, Ep. 2 has some interes$ng bits about logic at 29:09 et seq. and 39:06 et seq. URL: hlp://www.youtube.com/watch?v=-‐LGBWu-‐p22U&feature=related
• (The whole episode, in fact the whole series, is excellent and worth watching as is his earlier series Connec5ons. Both are now available on YouTube.)