Resources
Home » People » Karl Sherlock » English 120 » Resources » info | Logic & Reasoning
Pages within Resources

### Contact

Karl J. Sherlock
Associate Professor, English
Email: karl.sherlock@gcccd.edu
Office Hours: 558A (inside Bldg. 52)
Phone: 619-644-7871

# Logic and Argument

##### Relevant exercise:

xrcs | Logic & Argument

### LOGOS

appeal to intellect

• clinical/technical tone

• favoring facts and data over examples

• organizing arguments overtly into logical syllogisms

Example

### DEDUCTIVE REASONING

Deducting or Deducing: an act of taking away, or subtracting, leaving what remains

The use of syllogism to arrange a set of conditions or premises so that, through the act of logical subtraction, a definitive conclusion remains:

SYLLOGISM: an equation in which the truth of one premise and the true of another premise become a common truth: if p, then q; if q, then r: therefore, if p, then r.

Statements of "subtraction" and "conclusion" use the language of formal logic: if (when) . . . then; as a result; therefore; ergo; when . . . then; as a cause; in effect; etc.

An arrangement of premises:

MAJOR PREMISE: a general statement established as true and used as the basis on which to apply other premises

A = All men are mortals.

MINOR PREMISE: a more specific statement that relates to, or uses the language of, the Major Premise

B = Socrates is a man.

CONCLUSION: a specific assertion that is proven to be definitely or probably true and drawn from the Major and Minor Premise(s):

D = Therefore, Socrates is mortal.

Deductive Fallacies: errors in deductive reasoning caused by inconsistencies or errors in the way that the Major and Minor premises are presented, or in the methods of logic used to deduce the conclusions from them.

###### God is love, and love is blind. Stevie Wonder is blind, so Stevie Wonder is God.
• Major Premise: God is love.
• Minor Premise: Love is blind.
• Conclusion: God is blind.
• Major Premise: God is blind
• Minor Premise: Stevie Wonder is blind.
• Conclusion: Stevie Wonder is God.

Though the above seems logically reasonable because it uses simple "A-to-B, B-to-C" reasoning, it is faulty in its logic on a number of levels.

• Major Premise: All that is God [A] is love [B].
• Minor Premise: All that is love [B] is blind [C].
• Conclusion: All that is God [A] is blind [C].
• Major Premise: All that is God [A] is blind [C].
• Minor Premise: All that is Stevie Wonder [D] is blind [C].
• (Distribution Error: not all that is Blind [C] is Stevie Wonder [D].)
• Conclusion: All that is Stevie Wonder [D] is God [A].

Another problem with the above-mentioned syllogism is that it is guilty of EQUIVOCATION: the meaning of a key term changes or is used with multiple meanings. "Blind" does not mean physical blindness in the Major Premise and Minor Premise #1; rather, it is used as an analogy or a metaphor for the qualities of love that make one less aware of the faults in another. Therefore, the change in meaning from Minor Premise 1 to Minor Premise 2 shifts, and the conclusion is nonsensical. When the arguer intentionally shifts meanings without telling the audience or reader, this is said to equivocate, or "hide", the truth: it dissembles, and therefore is guilty of a lie by omission.

### Other Deductive Fallacies

Begging the Question (petitio principii)
Since I'm not lying, it follows that I'm telling the truth.

Non sequitur (does not follow)
If the mill were polluting the river then we would see an increase in fish deaths. And fish deaths have increased. Thus, the mill is polluting the river.

Post Hoc, Ergo Propter Hoc (post hoc reasoning; coincidental correlation)
Ice Cream Rape Study

False Dilemma
America: love it or leave it.

### INDUCTIVE REASONING

Inducting or Inducing: an act of bring in, or bringing about, into the open; to persuade by inferring the general significance of specific evidence or examples.

In logic, inductive arguments develop from specific examples, details or facts into conclusions that are, both, more general and probably true (as opposed to definitive conclusions in Deductive Reasoning).

###### Q. How can you tell an elephant has been in your refrigerator? A. There are elephant footprints in the butter.

The Specific Conditions are the evidence of footprints in the butter, from which a leap of inductive reasoning is made to assume that they can only be caused by an elephant.

Inductive Reasoning is a process of three major steps:

• HYPOTHESIS: An intuitive conclusion or a speculative answer to a question.
• EVIDENCE COLLECTION: An impartial example- or fact-gathering process
• INFERENCE: a answer to the hypothesis based on what can be known from the evidence; a generalization about what's probably true (not possibly true, but probably)

Inductive Fallacies: errors in inductive reasoning caused by flawed hypotheses, flawed methodologies for evidence gathering, or flawed methods of inference

Hasty Generalization (Sweeping Generalization)
I asked six of my friends what they thought of the new spending restraints and they agreed it is a good idea. The new restraints are therefore generally popular.

To see how Canadians will vote in the next election we polled a hundred people in Calgary. This shows conclusively that the Reform Party will sweep the polls. (People in Calgary tend to be more conservative, and hence more likely to vote Reform, than people in the rest of the country.)

False or Weak Analogies
Government is like business, so just as business must be sensitive primarily to the bottom line, so also must government. (But the objectives of government and business are completely different, so probably they will have to meet different criteria.)

Slothful (Lazy) Induction:
Hugo has had twelve accidents in the last six months, yet he insists that it is just a coincidence and not his fault. (Inductively, the evidence is overwhelming that it is his fault.

### PATHOS

appeal to emotion

poetical language and rhythms
allusions: literary and mythological
case examples, human interest

Example

Red Herring

Appeals to . . .

• patriotism
• fear
• jingoism
• like-ism
• bandwagon

### ETHOS

appeal to character (as opposed to "mores," which have to do with correct behavior)

• trustworthy
• truthful

Example

### Fallacies of Authority

Straw man

Doubtful Authority

Last Updated: 01/15/2016

### Contact

Karl J. Sherlock
Associate Professor, English
Email: karl.sherlock@gcccd.edu
Office Hours: 558A (inside Bldg. 52)
Phone: 619-644-7871

A Member of the Grossmont-Cuyamaca Community College District