11.2 Critical Reasoning: Implicit Assumptions, Strong vs Weak Arguments & Course of Action

Identify the claim before testing an assumption

An assumption is an unstated proposition that an argument relies on. Separate the evidence supplied, the conclusion drawn and the link between them. In the written CBT, the task is to reason from the statement. A plausible railway fact, a personal preference or a remembered rule cannot replace a missing premise.

For example, a fictional library wants to reduce waiting at its collection desk. It proposes moving prepaid collections to a separate counter, stating that this will free the main desk for other visitors. The evidence concerns congestion, the conclusion concerns a proposed change, and the required link is that the change can actually release some main-desk capacity. The statement does not imply that every visitor is dissatisfied or that separate counters solve every problem.

Distinguish necessary assumptions from helpful evidence. A necessary assumption is required by the stated reasoning. Helpful evidence can strengthen an argument without being indispensable. Read whether the question asks for an assumption, a conclusion, a strong argument or an appropriate action; these tasks require different tests.

Use the negation test carefully

For a proposed necessary assumption, negate its exact meaning and ask whether the argument loses a required link. Negation is a logical operation, not a switch to an exaggerated opposite.

In the library example, suppose the proposed assumption is that separating prepaid collections can free some capacity at the main desk. Negating it directly defeats the stated congestion rationale. By contrast, “every visitor prefers the new counter” is unnecessary: some visitors can dislike the change while it still frees capacity. Negating that preference does not defeat the argument.

The test is useful once the argument and its intended conclusion are clear. It does not provide automatic certainty about vague language, competing possible motives or an unstated implementation plan. A recommendation can have several possible justifications. Evaluate the justification actually supplied instead of inventing another motive to rescue it or demanding that every desirable feature be guaranteed.

Worked example: feasibility and relevance

A fictional dispatch office proposes that all prepaid parcels currently collected at its main desk be transferred to a spare counter during the same opening hours. It says the purpose is to reduce queues at the main desk. Assume the office intends to implement the proposal immediately, without changing staffing or opening hours.

Consider three candidate assumptions:

1. The spare counter has sufficient available capacity for the transferred collections under this plan.
2. Removing those collections can reduce the main desk's workload.
3. Prepaid parcels are heavier than every other parcel.

The first assumption supports feasibility within the expressly fixed staffing and hours. If the spare counter cannot accept the collections under those conditions, the plan cannot operate as proposed. The second connects the change to its stated purpose. The third has no supplied connection to queue length or desk capacity. It need not be true. Thus the first two are implicit in this stipulated argument; the third is irrelevant.

Notice what the example does not establish. It gives no measured reduction in waiting time, no guarantee of equal benefit for all visitors, and no proof that the spare counter is the cheapest possible solution. A necessary link should be expressed at the narrowest scope that the argument needs.

Evaluate the strength of an argument

A strong argument addresses the actual proposal with a relevant reason supported by the facts supplied. A weak argument can be irrelevant, circular, exaggerated or based on an analogy that does not preserve the important relationship. Agreement with the conclusion does not determine strength.

Suppose a fictional operator considers installing a warning device. The prompt stipulates that independent trials found fewer preventable incidents in comparable conditions. That evidence supports installation for the stated safety goal. An argument about the manager's favourite paint colour does not address effectiveness. An argument that unrelated offices bought furniture also fails to connect evidence to the decision.

A relevant objection can be strong too. If the prompt supplies reliable evidence that maintenance costs exceed the available budget and provides no funding alternative, feasibility is a legitimate issue. It does not logically erase the device's measured benefit; it raises another consideration. Two opposing arguments can both be relevant without either proving the entire policy decision alone.

Watch for familiar errors:

• False analogy: transferring a result between situations without showing that the relevant conditions match.
• Circular reasoning: assuming the conclusion in the reason offered for it.
• Unsupported causation: treating an association or a before-and-after change as proof of its cause.
• Overstatement: turning “may help some users” into “always solves the problem for everyone.”

Assess proposed courses of action

A course of action is a proposed response to the stated problem. Check whether it addresses the problem, is feasible under the supplied permissions and resources, and is proportionate to the evidence. An action can sound decisive while depending on facts that the prompt never establishes.

For a fictional equipment fault, suppose the approved plan expressly permits isolation, qualified inspection and notification of affected users. Activating that plan and arranging an inspection address the immediate concern. Dismissing the entire maintenance workforce before investigating is unsupported. Neither a study guide nor a generic reasoning exercise establishes real railway emergency procedures; an actual operating response depends on the applicable authorized instructions and facts.

Immediate containment and later investigation can both be appropriate when the prompt supports them. Do not reject one merely because the other also helps. Conversely, an investigation that leaves an explicitly stated immediate hazard unattended may fail to address the whole problem. Match the action to the question's timescale and avoid promises of zero future risk.

Verify the selected answer

Before choosing, state the conclusion, identify the evidence, and explain the link in one sentence. For an assumption, test its negation; for an argument, test relevance and support; for an action, test the stated authority, feasibility and proportionality. Recheck quantifiers such as all, some, only and never. These steps keep a logical deduction separate from speculation about what an organization might do.