Logical Reasoning — Statements, Arguments and Common Patterns

Logical reasoning is the art of moving from given information (premises) to a justified conclusion. CSS questions test whether you can do this strictly — distinguishing what truly follows from what merely sounds plausible.

1. Premises and conclusions

The first analytical step is always to identify the structure. Conclusion-indicator words include therefore, hence, thus, so, consequently. Premise-indicators include because, since, given that, as.

"The price of wheat will rise next month, because Russia has restricted exports and global demand is strong."

The conclusion is "the price of wheat will rise next month". The two premises are the export restriction and the strong demand.

2. Syllogisms

A syllogism is a three-statement deductive argument: two premises and a conclusion. The classic example:

• Premise 1: All men are mortal.
• Premise 2: Socrates is a man.
• Conclusion: Therefore, Socrates is mortal. Valid.

The most common syllogism trap is the undistributed middle:

• Premise 1: All doctors are educated people.
• Premise 2: Ali is an educated person.
• Conclusion: Therefore, Ali is a doctor. Invalid.

The middle term "educated people" does not establish that Ali falls into the doctor sub-group.

Worked Example 1 — Categorical syllogism

Some lawyers are politicians. All politicians are public figures. Which conclusion follows necessarily?

(a) All lawyers are public figures. (b) Some lawyers are public figures. (c) No politician is a lawyer. (d) Some public figures are not lawyers.

Draw three circles. The "some lawyers" overlap with "politicians", and "politicians" sit entirely inside "public figures". So those lawyers who are politicians are also inside "public figures" — at least some lawyers are public figures. Answer: (b).

(a) is too strong — only some lawyers, not all, are in the overlap. (c) directly contradicts the first premise. (d) is plausible in the real world but doesn't necessarily follow from the given premises.

3. Conditional reasoning

The form "If P, then Q" appears constantly. From it you can validly conclude:

• Modus ponens: P is true → Q is true. ✓
• Modus tollens: Q is false → P is false. ✓

But these inferences are invalid:

• Affirming the consequent: Q is true → P is true. ✗
• Denying the antecedent: P is false → Q is false. ✗

Worked Example 2 — Conditional trap

If it rains, the streets get wet. The streets are wet. Therefore it rained.

This is invalid — affirming the consequent. The streets could be wet for many reasons (a burst pipe, street cleaning, a flood from a river).

4. Strengthen, weaken and assumption questions

These are the most common analytical-reasoning question types.

• Assumption — what unstated belief is the author relying on? Test by negating the candidate: if negating it destroys the argument, it's an assumption.
• Strengthen — which fact would make the conclusion more likely?
• Weaken — which fact would make the conclusion less likely?

Worked Example 3 — Assumption

"Online education will replace traditional universities within twenty years, because internet access has reached 90% of the population and online platforms now offer the same content as universities."

What is the author assuming?

A natural answer: that students value the content of education more than the social and credentialing functions of a physical university. If we negate this — students actually value those functions highly — the argument collapses.

The core mental move in all of these is the same: separate what the author said from what they meant, and then check whether the inference between them really holds.