Logical Reasoning
The Logical Reasoning domain of the CBP Officer Entrance Examination tests whether you can take a short set of statements and determine what they do - and do not - force to be true. Items are verbal rather than mathematical: conditional rules, quantifier statements ("all," "some," "none"), ordering constraints, and brief arguments followed by questions such as "Which of the following must be true?" or "The argument depends on which assumption?" Every credited answer is provable from the text alone; outside knowledge of how ports or inspections really work is neither needed nor wanted.
Conditionals: four forms, two valid
Write each rule as sufficient → necessary. Only two inferences are valid: modus ponens (A→B; A; therefore B) and modus tollens (A→B; not B; therefore not A). The two classic errors are affirming the consequent (A→B; B; therefore A) and denying the antecedent (A→B; not A; therefore not B). Both appear as choices because they read fluently.
Translate connectives before you evaluate. "Only if" introduces the necessary condition: "X only if Y" means X→Y. "Unless" means "if not": "X unless Y" means not Y→X. "No A unless B" means A→B.
Quantifiers
"All A are B" says nothing about B outside A; reversing it is the most common trap. "Some A are B" means at least one, is reversible, and is compatible with "all." "No A are B" is reversible. Two "some" premises yield no conclusion, and "some" never justifies "most."
Worked example
Rule 1: If a traveler's bag is pulled for agricultural screening, the traveler's name is entered in the tracking log. Rule 2: No one in the tracking log may use the automated lane.
Case A: Maya's bag was pulled for screening. By Rule 1 she is in the log; by Rule 2 she may not use the automated lane. A valid chain.
Case B: Maya used the automated lane. The contrapositive of Rule 2 gives "not in the log." The contrapositive of Rule 1 then gives "bag not pulled for screening." Both conclusions follow, and neither form affirms the consequent.
Traps that cost marks
- Reversing a conditional or treating a sufficient condition as if it were necessary.
- Importing real-world procedure instead of reading the stated rule.
- Accepting an answer that could be true when the question demands must be true; test "must" by trying to build a counterexample.
- Reading "some" as "most," or "not all" as "none."
- Choosing the most sweeping option; words like "always" and "never" usually fail a quick counterexample.