1

A Little Logic

Identifying Parts of ArgumentsArguments are made of parts:

Premises (or support) Conclusion (or result) Inference (mental movement from premises to conclusion)

ConclusionPremisesInferenceDeductive Arguments

PremisesConclusion

Types of Arguments: Deductive and InductiveDeductive PremisesIf theres time in the day, Ill be pleased.If I am pleased, then life is worth living.

ConclusionIf there is time in the day, then life is worth living.

(2 x 150)/30 = 30

Inductive Arguments

PremisesConclusion

InductivePremise: Seventy-five percent of all 8.0 or greater magnitude earthquakes studied in the last 50 years have had 10 to 20 aftershocks per day, leading to one major 8.0 magnitude aftershock within 1 year of the initial quake.

Conclusion: Therefore, the 9.0 earthquake of 11 March 2011, off the coast of Sendai, Japan, will result in a major aftershock of 8.0 magnitude.

as indicated byasbecausefor the reason thatfor given thatin thatinasmuch asmay be inferred fromowing toseeing thatsince

Premise indicators: accordingly, as a result, consequently,entails thatfor this reason, hence, implies thatit follows thatit must be thatsotherefore,thus, we may concludewe may infer thatwherefore

Conclusion indicators: Since the good, according to Plato, is that which furthers a persons real interests, It follows that in any given case when theGood is known, men will seek it.

(from Avrum Stroll and Richard Popkin, Philosophy and the Human Spirit)

A dog was kept in the stalls, and yet, though someone had been in and fetched out a horse, the dog had not barked. Obviously, the visitor was someone the dog knew well

(Sherlock Holmes, The Adventure of the Silver Blaze)

It is difficult to gauge the pain felt by animals, because pain is subjective and Animals cannot talk.

Modus PonensHere is an example:

If the USA continues to invade other Muslim countries, then its prestige and image will fall in the Muslim world.

The USA does continue to invade other Muslim countries.

Therefore, the prestige and image of the USA will fall in the Muslim world.

If p, then q. P Therefore, qModus TollensIf children today are intensively taught cursive writing, then they will be able to read cursive writing.

But children today have a difficult time reading cursive writing.

Therefore, children today are not taught cursive writing very intensively.

If p, then q. Not q. Therefore, not p.Hypothetical SyllogismIf theres time in the day, Ill bepleased.If I am pleased, then life is worth living.Therefore, if there is time in the day, then life is worth living.

If p, then q. If q, then r. Therefore, if p, then r.Disjunctive SyllogismEither I will buy a BMW or a Mercedes.I decided not to buy a Mercedes.Therefore, I decided to buy a Mercedes instead.

p or q Not q. Therefore, p.Constructive DilemmaIf we pollute the environment, human health will decline, but if we recycle, then human health will improve.Either we pollute or we recycle.Therefore, either human health will decline or it will improve. If p, then q and if r, then s. p or r Therefore, q or s.