1. The Anatomy of a Flaw
In formal logic, a "flaw" isn't necessarily a lie. It is a lack of sufficiency. The premises might be 100% true, but they fail to guarantee the conclusion because the author overlooked a critical variable.
| Component | Definition | Example (Inflation) |
|---|---|---|
| Premise | Factual observation. | Savings were higher in the 70s (high inflation) than the 80s (low inflation). |
| Conclusion | The claim to be proven. | Therefore, high inflation does NOT discourage saving. |
2. Pattern 1: The "Other Factors" Flaw (Easy)
This flaw occurs when an author observes a correlation (X happened with Y) and assumes causation, ignoring external variables.
"It is often said that high rates of inflation tend to diminish people's incentive to save and invest. This view must be incorrect, however, because people generally saved and invested more of their income in the 1970's when inflation rates were high than they did in the 1980's when inflation rates were low."
Of the following, the best criticism of the argument above is that it overlooks the possibility that
- (A) all people do not respond in the same way to a given economic stimulus
- (B) certain factors operating in the 1980's but not in the 1970's diminished people's incentive to save and invest
- (C) the population was larger in the 1980's than it was in the 1970's
- (D) the proponents of the view cited would stand to gain if inflation rates become lower
- (E) a factor that affects people's savings behavior in a certain way could affect people's investment behavior quite differently
Solution Walkthrough: Inflation vs Savings
Correlation does not equal Causation.
Step 1The Logic Gap
The author treats the decades as a controlled experiment. But the world changes!
Maybe something else (like unemployment or taxes) made people save less in the 80s, despite low inflation.
Step 2The Flaw (Option B)
(B) certain factors operating in the 1980's... diminished people's incentive to save...
This points out the missing variable. If other factors killed savings in the 80s, then the low inflation might still have been 'trying' to help, but was overpowered.
Step 3Why it breaks the argument
By ignoring these external factors, the author fails to prove that inflation has no effect.
3. Pattern 2: The "Incompatible Goals" Flaw (Medium)
A solution designed for one goal (Profit) often fails when applied to a situation with a conflicting mandate (Public Service).
"Public-sector (government-owned) companies are often unprofitable and a drain on the taxpayer. Such enterprises should be sold to the private sector, where competition will force them either to be efficient and profitable or else to close."
Which of the following, if true, identifies a flaw in the policy proposed above?
- (A) The revenue gained from the sale of public-sector companies is likely to be negligible compared to the cost of maintaining them.
- (B) By buying a public-sector company and then closing the company and selling its assets, a buyer can often make a profit.
- (C) The services provided by many public-sector companies must be made available to citizens, even when a price that covers costs cannot be charged.
- (D) Some unprofitable private-sector companies have become profitable after being taken over by the government to prevent their closing.
- (E) The costs of environmental protection, contributions to social programs, and job-safety measures are the same in the public and private sectors.
Solution Walkthrough: Privatization
Plan: Privatize to force efficiency or closure.
Step 1The Logic Gap
The plan assumes the only goal is profit/efficiency. It ignores the purpose of public companies.
Step 2The Flaw (Option C)
(C) The services... must be made available... even when a price that covers costs cannot be charged.
This highlights the 'Mandate'. Some services (like rural mail or public transit) are supposed to lose money to serve the public.
Step 3Why the Plan Fails
If you privatize these, the private company will simply close them (as the argument admits). But if the service is essential, the government can't let it close. The solution is incompatible with the mandate.
4. Pattern 3: The "Missing Numbers" Flaw (Hard)
The most subtle flaw involves proportions. An author uses a small percentage to dismiss a group, forgetting that the other group might be even smaller.
"Colorless diamonds can command high prices as gemstones. A type of less valuable diamonds can be treated to remove all color. Only sophisticated tests can distinguish such treated diamonds from naturally colorless ones. However, only 2 percent of diamonds mined are of the colored type that can be successfully treated, and many of those are of insufficient quality to make the treatment worthwhile. Surely, therefore, the vast majority of colorless diamonds sold by jewelers are naturally colorless."
A serious flaw in the reasoning of the argument is that
- (A) comparisons between the price diamonds command as gemstones and their value for other uses are omitted
- (B) information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless, gemstone diamonds
- (C) the possibility that colored diamonds might be used as gemstones, even without having been treated, is ignored
- (D) the currently available method for making colorless diamonds from colored ones is treated as though it were the only possible method for doing so
- (E) the difficulty that a customer of a jeweler would have in distinguishing a naturally colorless diamond from a treated one is not taken into account
Solution Walkthrough: The Diamond Ratio
Claim: Treated diamonds are rare (2%), so most sold diamonds must be Natural.
Step 1The Logic Gap
The author says 'Treated < 2%'. Is that small? It depends on how big the 'Natural' group is.
What if Natural Colorless diamonds are 0.001% of all diamonds?
Step 2The Flaw (Option B)
(B) information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless... diamonds
We are missing the denominator for the other side of the equation.
Step 3The Math Check
If Treated = 2% of total.
And Natural = 0.1% of total.
Then Treated > Natural (10x more common!).
The conclusion would be false. We need both numbers to compare.
Summary: The Flaw-Finder Checklist
- Other Factors: Did the author ignore external variables (Correlation vs Causation)?
- Incompatible Goals: Does the 'Profit' solution fail the 'Service' mandate?
- Missing Numbers: Did they give you a % for Group A but nothing for Group B?
