Arguments • Arguments are lines of reasoning using propositions (claims or assertions) • Propositions come in 3 forms: factual claims, opinions and ideas (including hypotheses and theories) • Premise/Conclusion structure
Examples of Arguments • You shouldn’t hit people, Johnny. Hitting hurts people, and it’s wrong to hurt people. • My client was at the bar when the murder occurred. Several eyewitnesses have reported seeing him there, and his receipt indicates that he didn’t leave until after the murder occurred. Thus, he could not have committed the murder • If the Cubs want to start winning, they need to redesign their uniforms. This always seems to give teams a new, winning attitude. You know, kind of a break from the losing days of the past. • Bill cheated on you once before; he’ll do it again. Men like that just don’t change.
2 Key Distinctions • Strong v. Persuasive arguments: Arguments are strong (or cogent) if they are well reasoned; arguments are persuasive if they succeed in convincing. Strong arguments are not necessarily persuasive; persuasive arguments are not necessarily strong. • Descriptions v. Inferences: Descriptions are reports; inferences are conclusions from or interpretations of those reports.
Assumptions • Many arguments contain assumptions or missing premises—i.e., incomplete presentations of the argument. • Assumptions can be warranted or unwarranted
When are assumptions warranted? • Readily available evidence • Factual claim shared with target audience • Value claim shared with target audience
When are assumptions unwarranted? • Based on speculation • Based on evidence not readily available • Disagreement over factual matters • Disagreement over value judgments
Some Examples • It’s wrong to spank your children because it’s abusive. • We should put tighter restrictions on divorce. As Jesus told us, “What God has joined, let no man sunder”. • Jim wouldn’t have developed lung cancer if he had quit smoking. • It was wrong of us to go to war in Iraq, because it’s killing innocent people.
Types of Evidence I Speculation or Opinion Circumstantial Evidence Cause/Effect Reasoning All these are evaluated by abductive methods—by Inference to the Best Explanation
Types of Evidence II Testimony Evaluated by: observation interest background information personal characteristics cultural factors expertise
Types of Evidence III Factual claims Statistical data Evaluated by empirical observation and analysis
Types of Evidence IV Value claims (incl. taste, aesthetic judgment, moral judgment) Analogies (including Precedents) Conditional claims Evaluated by coherence, relevance and applicability
Multi-Step Arguments • Some arguments have preliminary conclusions as steps toward a major conclusion • Some arguments provide evidential support for their premises ^ These are called Lemmas
An Example: William Lane Craig’s Cosmological Argument P1: Everything that begins to exist has a cause P2: The Universe began to exist L1: Big Bang Cosmology L2: The logical impossibility of an actual infinite PC1: Therefore, the Universe began to exist P3: Nothing can cause itself to exist PC2: Therefore, something else caused the Universe to exist P4: The only plausible cause for the Universe is God L3: Because God is omnipotent and omniscient C: God caused the Universe to exist