8.4 Separating Stated Facts From Assumptions

Do Not Supply Missing Facts

The most common way to fail a deductive item is to add a fact the prompt never gave you. IOS states plainly that the CJBAT requires no previous experience and no outside knowledge — every needed rule and fact is in the question. A stated fact is information printed in the prompt. An assumption is information you supply from common sense, life experience, television, or guesses about how agencies operate. Even a highly plausible assumption is not a valid deduction unless the prompt supports it.

This is harder than it sounds, because the scenarios are written to feel real. A passage about a traffic stop, a booking, or a cell-block count invites you to fill gaps with what you imagine "really happens." The test rewards the opposite instinct: reason strictly from the printed words.

The S / C / N Audit

A reliable habit is to label each answer choice as you read it:

• S — Supported: every part of the choice follows from the rule and stated facts.
• C — Contradicted: the choice conflicts with the rule or a stated fact.
• N — Not enough information: the choice could be true but the prompt never establishes it.

The correct deductive answer is almost always the S choice. C choices are eliminated immediately. N choices are the dangerous ones — they often sound the most realistic, but "could be true" is not "must be true."

Worked Example

Rule: Booking staff may release personal property to an arrestee at release only if the property was logged at intake and the arrestee signs the release form. Facts: At intake, a wristwatch was logged for arrestee Pham. At release, Pham asks for the watch and a phone. The phone does not appear on the intake log. Pham signs the release form.

Label the candidate conclusions:

• "The watch may be released to Pham." — S: it was logged at intake and Pham signed; both conditions met.
• "The phone may be released to Pham." — C: the phone was not logged at intake, so a required condition fails.
• "Pham was carrying the phone when arrested." — N: nothing in the prompt establishes this; it is an assumption about how the phone got there.

The correct deduction is that the watch may be released but the phone may not. The pull toward releasing the phone — "surely it's his" — is exactly the assumption the rule does not support.

A Discipline, Not A Trick

Deductive reasoning is often less about complex logic and more about restraint. Use this assumption check:

• Ask of every answer: where did the prompt say that?
• Separate what the rule requires from what is realistic.
• Treat "usually," "probably," and "in my experience" as red flags.
• Do not import agency procedures the scenario never states.
• Prefer the answer that stays inside the prompt over the one that adds convincing detail.

When you refuse to add facts, most trap answers reveal themselves. The choice that sounds thorough because it brings in extra real-world detail is usually the very one carrying an unsupported assumption. The answer that says only what the rule forces — no more — is the deductively correct one.

Necessary Assumptions Versus Smuggled Assumptions

There is one nuance worth understanding. Logicians distinguish a necessary (warranted) assumption — a fact the rule itself logically requires — from a smuggled assumption, which is an extra fact the reader imports. CJBAT deductive items are built so that the answer needs no smuggled assumption: everything required is on the page. If you find yourself thinking "this would be true as long as such-and-such," and that such-and-such is not stated, you have spotted a smuggled assumption and should reject the choice.

A few high-frequency smuggled assumptions to watch for:

• Time and sequence: assuming events happened in a particular order when the prompt gives only what occurred, not when.
• Cause: assuming one fact caused another because they appear together. Correlation in a prompt is not stated causation.
• Completeness: assuming a list is exhaustive ("these are the only exceptions") when the prompt never says it is complete.
• Identity: assuming two differently named things are the same person, item, or category.
• Continuity: assuming a condition that was true earlier is still true later, when the prompt does not say it persisted.

Worked example. Prompt: "At 2 p.m. the cell block was at full capacity. At 4 p.m. two inmates were transferred out." A choice reads: "At 4 p.m. the cell block was below full capacity." That requires the continuity assumption that no inmates were added between 2 and 4 p.m. — which the prompt never states. So the choice is not a valid deduction; it smuggles in a fact about intake. The only thing the prompt forces is that two inmates were transferred out, not the net population at 4 p.m.

The discipline, then, is twofold: accept only conclusions the rule necessarily warrants, and reject any conclusion that survives only because you quietly supplied an extra premise. Naming the smuggle — order, cause, completeness, identity, continuity — turns a vague unease about an answer into a concrete reason to eliminate it. This is the single most transferable habit in the deductive section, and it carries directly into the inductive items in the next chapter.