PHIL 210 Study Guide - Quiz Guide: Deductive Reasoning, Formal System, Classical Logic

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PHIL 210-Critical Thinking
Book Notes
Chapter 1 The parts of public thinking deductive argument
Study notes 2
Definition 2: Arguments are linguistic or logical object
o Argument is a set of sentences or propositions, factoring out considerations about the
speaker, the audience, the context, and the boarder goal of the argument
This set aside if audience will find it reasonable
Also if it’s viewed as practical complication that rises when speakers use the
argument
i.e: good argument is defined as the truth of the premises and their logical
relation to the conclusion, without mention of the speaker, listener, or context
In this sense a good argument is defined as Sound,
meaning Valid: premises are all relevant to conclusion, in a way that if
premises are true, conclusion must be true (NO WAY FOR PREMISE TO BE
TRUE AND CONCLUSION TO BE FALSE)
and All True Premises
o More precisely, all Essential Premises (premises that event when irrelevant
premises are removed, remain) must be true.
So if argument fails, we can fix it to see whether its invalid or the premises are
not true
Soundess doesn’t depend on how effective it is
An argument can be sound, so good Def 2, but there is evidence to show that is should not be
accepted, bad Def 1.
o Ex: Either there is a new species of lizard in hiding in the amazon or 5+5=11,
o It’s false that 5+5=11,
o Therefore, there is a new species of lizards hiding in the amazon
This argument is Valid (Disjunctive Syllogism), and would also be sound because its
premises are true in the situation described.
But in giving this sound argument by accident, without reason to believe the first part of first
premise, this argument doesn’t do what arguments are supposed to do, which is give
reasonable grounds to believe the conclusion.
o Therefore, when giving arguments, not only important to give premises that are true, but
also important that premises are mutually accepted between you and audience, if you not
only want to give sound arguments but one also able to convince a reasonable person.
We forget this ^^ when we focus too much on Definition 2
In terms of communicating an argument (Def 1), the issue of acceptable premise often leads
to some degree regree of justification (when you need to make a new argument to support a
premise you previously made because it wasn’t supported by the audience)
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