1. The Architecture of Logic
To the untrained eye, Passage Completion questions look like creative writing. To the architect of logic, they are incomplete blueprints. Every argument is a journey from Evidence to Conclusion. When a passage ends with a blank, it means there is a gap in the structural support.
| Component | Role | What to Look For |
|---|---|---|
| The Situation | The Facts | Foundational data, context, and physical laws. |
| The Reasoning | The Logic Path | The rule that dictates how facts interact. |
| The Conclusion | The Destination | The final claim the author is trying to prove. |
2. Level 1: Finding the Factual Bridge (Easy)
At the foundational level, the missing link is often a specific coordinate or measurement required to trigger a known rule.
"Within the earth's core, which is iron, pressure increases with depth. Because the temperature at which iron melts increases with pressure, the inner core is solid and the outer core is molten. Physicists can determine the melting temperature of iron at any given pressure and the pressure for any given depth in the earth. Therefore, the actual temperature at the boundary of the earth's outer and inner cores—the melting temperature of iron there—can be determined, since ________"
Which of the following most logically completes the argument?
- (A) the depth beneath the earth's surface of the boundary between the outer and inner cores is known
- (B) some of the heat from the earth's core flows to the surface of the earth
- (C) pressures within the earth's outer core are much greater than pressures above the outer core
- (D) nowhere in the earth's core can the temperature be measured directly
- (E) the temperatures within the earth's inner core are higher than in the outer core
Solution Walkthrough: The Iron Core
We have the formulas (Depth -> Pressure -> Melting Point), but we lack the input variable.
Step 1The Logic Chain
1. Depth determines Pressure.
2. Pressure determines Melting Point.
3. At the boundary, Actual Temp = Melting Point.
Step 2The Gap
We have the conversion tools, but we don't know WHERE the boundary is. We are missing the coordinate.
Step 3The Bridge (Option A)
(A) the depth... of the boundary... is known.
This provides the missing input. Knowing the depth allows us to calculate pressure, which gives us the temperature. Correct.
3. Level 2: Reconciling Contradictions (Medium)
When an argument presents a paradox (two facts that seem to negate each other), the missing link is often an exceptional condition like timing or duration.
"A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since ________"
Which of the following most logically completes the argument?
- (A) the spot was not the brightest object in the photograph
- (B) the photograph contains many streaks that astronomers can identify as caused by noncelestial objects
- (C) stars in the night sky do not appear to shift position relative to each other
- (D) the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open
- (E) if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects
Solution Walkthrough: The Night Sky
Paradox: The object was MOVING, but it appears as a STATIONARY DOT. How?
Step 1The Logic Gap
If the shutter is open for a long time, any moving light should create a line (streak). A dot implies it didn't move across the film.
Step 2The Resolution (Option D)
(D) the spot... emitted a flash that lasted for only a fraction of the time...
If the light was only on for a split second, the camera only captured it at one specific point. It moved in the dark, so no streak was recorded.
Step 3Why (C) is a Trap
(C) states a general truth about stars, but it doesn't explain the specific paradox of this moving object appearing stationary.
4. Level 3: Predicting Counter-Forces (Hard)
The highest level involves abstract synthesis. You must identify an "Invisible Variable" (like internal consumption) that offsets an obvious trend.
"Utrania was formerly a major petroleum exporter, but in recent decades economic stagnation and restrictive regulations inhibited investment in new oil fields. In consequence, Utranian oil exports dropped steadily as old fields became depleted. Utrania's currently improving economic situation, together with less-restrictive regulations, will undoubtedly result in the rapid development of new fields. However, it would be premature to conclude that the rapid development of new fields will result in higher oil exports, because ________"
Which of the following most logically completes the argument?
- (A) the price of oil is expected to remain relatively stable over the next several years
- (B) the improvement in the economic situation in Utrania is expected to result in a dramatic increase in the proportion of Utranians who own automobiles
- (C) most of the investment in new oil fields in Utrania is expected to come from foreign sources
- (D) new technology is available to recover oil from old oil fields formerly regarded as depleted
- (E) many of the new oil fields in Utrania are likely to be as productive as those that were developed during the period when Utrania was a major oil exporter
Solution Walkthrough: The Oil Trap
Premise: Production is going UP.
Conclusion: Exports might NOT go up.
Step 1The Logic Gap
Normally, More Production = More Exports. What could break this link?
Exports = Production - Domestic Consumption.
Step 2The Missing Variable (Option B)
(B) ...dramatic increase in the proportion of Utranians who own automobiles.
More cars = More domestic oil use. This 'Internal Drain' eats up the new supply before it can be exported.
Step 3The Directional Traps
Options (C), (D), and (E) are all 'Good News' for production. They strengthen the idea that exports WILL rise, which is the opposite of what we need.
Summary: The "Distractor" Matrix
Mastery comes from recognizing the wrong answers as quickly as the right ones.
- The Vague Irrelevancy: Topically related but lacks the specific data point (e.g. heat flow).
- The General Truth: A true fact that doesn't solve the specific paradox (e.g. star positions).
- The Directional Reversal: A strong logical link that supports the opposite conclusion (e.g. new technology).
