Next CSE-PPT: 14 March 2027 · Professional & Subprofessional
Civil Service Exam Professional reviewer on deductive reasoning: syllogisms with all, some and no, conditional statements, contrapositives, negations, "unless" and "only", and conclusions that do not follow.
Deductive reasoning asks what must be true if the given statements are true, whether or not they match real life. The CSC describes Analytical Ability as including identifying assumptions and conclusions and logical reasoning, and syllogisms are a classic way to practise both.
Draw a quick circle diagram for "all", "some" and "no" statements, and remember the two valid patterns for "if … then": if P then Q, and P is true, so Q is true; if P then Q, and Q is false, so P is false.
Correct answer: B. All clerks in the agency are covered by the GSIS.
If every clerk is a civil servant and every civil servant is covered, then every clerk is covered. The reverse, that all GSIS members are clerks, does not follow. "Some civil servants are not clerks" may be true but is not stated.
Read detailsCorrect answer: B. No auditor is a cashier.
Every auditor is inside the group of supervisors, and that group shares no member with the cashiers. So no auditor can be a cashier. Nothing says all supervisors are auditors.
Read detailsCorrect answer: A. Some reports are returned to the sender.
The late reports are some of the reports, and all of them are returned. So at least some reports are returned. We cannot say all are, and we cannot say every returned report is late.
Read detailsCorrect answer: C. None of these conclusions necessarily follows.
The engineers among the graduates may or may not include any applicants. Since "some applicants are engineers" and "no applicant is an engineer" are both possible, neither must be true.
Read detailsCorrect answer: B. Maria did not pass the CSE.
From "if P, then Q" and "not Q", we may conclude "not P". If passing always leads to an eligibility, someone without one cannot have passed. This valid pattern is called denying the consequent.
Read detailsCorrect answer: A. It cannot be determined whether the office is closed.
The statement says what happens on holidays but not on other days. The office might close for other reasons, such as a typhoon. Concluding that it is open is the error called denying the antecedent.
Read detailsCorrect answer: C. The folder is on the director's desk.
When exactly two possibilities are given and one is ruled out, the other must be true. This is a disjunctive syllogism: either A or B; not A; therefore B.
Read detailsCorrect answer: A. If a person is not at least 35 years old, then the person is not a senator.
Every "if P, then Q" statement is equivalent to its contrapositive, "if not Q, then not P". The second option reverses the statement (its converse) and the third negates both parts (its inverse); neither is equivalent.
Read detailsCorrect answer: A. No files are missing.
The negation of "some are" is "none are". If it is false that at least one file is missing, then no file is missing. "Some files are not missing" can be true at the same time as the original statement.
Read detailsCorrect answer: C. The office is not open, or the clerk is not present.
An "and" statement is false when at least one part is false. So its negation is "not the first, or not the second". This rule is known as De Morgan's law.
Read detailsCorrect answer: A. The conclusion does not follow from the statements.
The animals that are dogs need not include any cats. True statements do not guarantee a valid conclusion; the conclusion must follow from the way the groups are related.
Read detailsCorrect answer: D. If someone uses the gym, that person is a registered employee.
"None but" means "only". Only registered employees may use the gym, so anyone using it must be registered. It does not say that every registered employee actually uses it.
Read detailsCorrect answer: C. Ana did not pass the interview.
"All except Ana" means every applicant other than Ana passed, and Ana did not. The sentence also implies that Ana was one of the applicants.
Read detailsCorrect answer: D. New staff will be hired.
Linked conditionals form a chain: approved → project starts → staff hired. Since the first condition is met, every later step follows. This is sometimes called a hypothetical syllogism.
Read detailsCorrect answer: A. Some managers are not doctors.
The managers who are lawyers cannot be doctors, so at least some managers are not doctors. We cannot say that no manager is a doctor, since the managers who are not lawyers might be.
Read detailsCorrect answer: B. Some squares are not quadrilaterals.
Since every square is a rectangle and every rectangle is a quadrilateral, every square is a quadrilateral. So "some squares are not quadrilaterals" contradicts the statements and must be false.
Read detailsCorrect answer: B. If you vote, then you have registered.
"Unless P, not Q" means "if not P, then not Q": if you do not register, you cannot vote. Its contrapositive is "if you vote, you registered". Registering does not guarantee that you will vote.
Read detailsCorrect answer: D. No one entitled to leave credits is a contractual worker.
A "no" statement can be reversed without changing its meaning: if no A is B, then no B is A. The groups simply do not overlap.
Read detailsCorrect answer: C. All whales breathe air.
Whales are inside the group of mammals, which is inside the group of air-breathers, so all whales breathe air. "Some mammals are not whales" is true in real life but does not follow from these two statements.
Read detailsCorrect answer: D. The printer was not out of ink.
From "if P, then not Q" and "Q is true", we conclude "not P". Since the report was printed, the printer could not have been out of ink, assuming the report was printed on this printer as the statement implies.
Read details