AILET Logical Reasoning – Assumptions
AILET (All India Law Entrance Test) – Logical Reasoning
Topic: Assumptions
1. Simple Explanation
An assumption is an unstated premise that must be true for an argument to hold.
In a logical argument, the author often assumes something that isn’t explicitly mentioned.
If that assumption is false, the conclusion can become invalid or the argument weakens.
Analogy:
Think of an argument like a chain.
Each link (premise) must be solid; an unseen link (assumption) keeps the chain from breaking.
2. Key Points
| # | Concept | What to look for |
|---|---|---|
| 1 | Definition | An unstated premise that must be true for the argument’s conclusion to follow. |
| 2 | Types of Assumptions | • Necessary: If it were false, the conclusion would be false. • Sufficient: If it were true, the conclusion would be true (though other conditions may also suffice). |
| 3 | Common Assumption Forms | • Causal (If A, then B → assumes A causes B).• Causal‑Inverse (Assumes a cause for an effect). • Statistical (Assumes a general rule from a sample). • Generalization (Assumes a property of a part applies to the whole). |
| 4 | Assumption vs. Premise | Premise = explicitly stated. Assumption = implicit, not stated. |
| 5 | Assumption Identification Steps | 1. Write down the explicit premises and conclusion. 2. Draw a flow diagram or logical tree. 3. Look for “jumps” where a link is missing. 4. Propose a missing premise that would fill the gap. |
| 6 | Common Mistakes | • Assuming a necessary premise instead of a sufficient one. • Ignoring that an assumption can be false (which invalidates the argument). |
| 7 | Practice Tip | Turn the argument into a conditional chain and see if any step needs an extra link. |
3. Worked Example
Argument
All students who pass the exam are awarded a scholarship.
John passed the exam.
Therefore, John is awarded a scholarship.
Step‑by‑Step Identification
| Step | What’s Given | Observation |
|---|---|---|
| 1 | Premise 1: All students who pass the exam are awarded a scholarship. | This is a universal conditional. |
| 2 | Premise 2: John passed the exam. | A specific instance of the universal. |
| 3 | Conclusion: John is awarded a scholarship. | The logical inference. |
Is any assumption hidden?
- The conclusion follows directly from the two premises.
- No extra premise is needed → No hidden assumption.
Now a trickier argument
All employees who work overtime get a bonus.
Maria works overtime.
Therefore, Maria gets a bonus.
Hidden Assumption?
- Premise 1: All employees who work overtime get a bonus.
- Premise 2: Maria works overtime.
- Conclusion: Maria gets a bonus.
Missing link?
No missing premise. But notice: Premise 1 says all employees. If Maria is not an employee (e.g., a contractor), the conclusion fails.
Thus the argument implicitly assumes that Maria is an employee.
Explicit Assumption: Maria is an employee.
Another Classic Example
Argument
If it rains, the streets are wet.
The streets are wet.
Therefore, it rained.
Assumption Identification
- Premise: If it rains, the streets are wet. (Conditional)
- Premise: The streets are wet. (Observation)
- Conclusion: It rained.
Missing Assumption: There are no other causes for the streets being wet.
In formal terms, the argument assumes the converse of the conditional, which is not logically warranted.
Hence, the assumption is false → the argument is invalid.
4. Quick Revision Summary
- Assumption = unstated premise required for a conclusion to hold.
- Identify: Draw premises → conclusion → spot gaps → propose missing premise.
- Types: Necessary, Sufficient, Causal, Statistical, Generalization.
- Common trap: Confusing an implicit premise with the converse of a conditional.
- Practice: Convert arguments into flow charts; test each link.
- Remember: If you can prove the conclusion without the assumption, the argument is logically sound. If you can falsify the conclusion by making the assumption false, the argument is invalid.
Tip: In AILET, you’ll often be asked to choose the most plausible assumption. Look for the one that fits naturally into the flow of the argument and does not introduce unrelated concepts.
Good luck, and keep practicing!