Logic 2 PYQs Answer (2018-2019)
Logic II - Question Paper (QP Code: 25492)
Answers for 2nd Year B.A. LL.B.
Q.1 Answer in one or two sentences:
(a) Define mediate inference. Give an example.
Ans: Mediate inference is reasoning where the conclusion is derived from two or more premises.
Example: All men are mortal; Socrates is a man; therefore, Socrates is mortal.
(b) Give an example of ambiguous minor term in categorical syllogism.
Ans: Example: All banks are beside rivers. All banks are financial institutions. Therefore, all financial institutions are beside rivers.
(c) Give the symbolic expression of pure hypothetical syllogism.
Ans: If P → Q, and Q → R, therefore P → R.
(d) Symbolise and state the Rule of Inference: “If he is guilty, he will be punished. He is guilty; therefore, he will be punished.”
Ans: Let G = He is guilty, P = He will be punished.
Symbolically: G → P, G ⸫ P (Modus Ponendo Ponens).
(e) Symbolise and state the Rules of Replacement: “It is false that the officer is corrupt and he has to be punished” is equivalent to “Either it is not true that the officer is corrupt or he should not be punished.”
Ans: ~(p • q) ≡ (~p ∨ ~q). This is according to De Morgan’s Law.
(f) Give an example of Complex Destructive Dilemma.
Ans: If it rains, the match will be cancelled; if it is hot, the players will suffer. Either it will rain or it will be hot. Therefore, either the match will be cancelled or the players will suffer.
(g) Reduce directly DATISI.
Ans: DATISI is reduced to Darii (First figure) by direct reduction using conversion of the minor premise.
(h) State the difference between Modus Ponendo Tollens and Modus Tollendo Ponens.
Ans: Modus Ponendo Tollens denies one part of a disjunctive proposition by affirming the other; Modus Tollendo Ponens affirms one by denying the other.
(i) What are the conditions to establish a hypothesis?
Ans: The conditions are — (1) It must explain facts, (2) It must be consistent, (3) It must be verifiable, (4) It must be simple and adequate.
(j) Define a hypothesis.
Ans: A hypothesis is a provisional explanation of facts, assumed for the sake of reasoning or investigation.
Q.2 Write short notes on (any four):
(a) Prove the special rules of figure I of categorical syllogism.
Ans: Special rules of Figure I: (1) The major premise must be universal. (2) The minor premise must be affirmative. These rules ensure that the middle term is distributed once and proper inference is drawn.
(b) Fallacy of petitio principii and amphiboly.
Ans: Petitio principii (begging the question) assumes the conclusion in the premise. Amphiboly arises due to grammatical ambiguity in a sentence.
(c) Directive and expressive use of language.
Ans: Directive use aims to cause action (e.g., commands, requests). Expressive use conveys feelings or emotions (e.g., exclamations).
(d) Volunti-non-fit-injuria.
Ans: It means “to a willing person, no injury is done.” If one consents to a risk or harm, they cannot claim injury under law.
(e) Any three impediments to good reasoning (Richard Feldman).
Ans: (1) Bias, (2) Ignorance, (3) Prejudice — these hinder logical thinking and objectivity in reasoning.
(f) Emotive words.
Ans: Emotive words are words used to express or evoke emotions rather than convey factual information, e.g., “brave,” “evil,” “heroic.”
Q.3 Attempt any two questions:
(a) Test the validity of the following categorical syllogism. Identify the figure. Give reasons.
(i) All rational beings are responsible for their actions. No lower animals are rational beings. Therefore, no lower animals are responsible for their actions.
Ans: Figure 1; Mood = Celarent (EAE). Valid by Rule: The middle term is distributed once, and there is no undistributed middle.
(ii) All Frenchmen are Europeans. All Germans are Europeans. Hence, all Germans are Frenchmen.
Ans: Invalid; Fallacy of Undistributed Middle. The middle term “Europeans” is undistributed.
(b) Reduce indirectly: BAROCO
Ans: BAROCO (Third figure) is reduced indirectly to Barbara of the first figure by obversion and conversion of premises.
(c) Identify the following fallacy. Give reasons:
(i) The Lokpal Bill is passed by the Parliament. Mr. Tiwari is a member of the Legislative Assembly. Therefore, Mr. Tiwari must have voted for the Bill.
Ans: Fallacy of False Analogy – both legislative bodies are different.
(ii) The machine is made of material substance. Every part of the machine is made of matter.
Ans: Fallacy of Composition – what is true of the whole is wrongly applied to parts.
(iii) This strike is illegal. If the workers do not report for duty within three days, their services will be terminated.
Ans: No fallacy; this is a conditional statement expressing consequence.
Q.4 Answer any two (A) and any three (B):
(A)(a) What is the dictum of Aristotle? Show how the dictum forms the basis of all types of categorical syllogistic reasoning.
Ans: Aristotle’s dictum — “Whatever is affirmed or denied of a whole class may be affirmed or denied of anything contained in that class.” It serves as the fundamental principle behind all valid categorical syllogisms.
(b) Explain the following:
(i) Argumentum ad misericordiam and Argumentum ad populum.
Ans: Ad misericordiam appeals to pity; Ad populum appeals to public opinion or popularity instead of logic.
(ii) Kinds of agreement and disagreement.
Ans: (1) Agreement in belief, (2) Agreement in attitude, (3) Disagreement in belief, (4) Disagreement in attitude.
(c) Explain with examples any three kinds of Hypothesis.
Ans: (1) Descriptive hypothesis – describes a fact.
(2) Explanatory hypothesis – explains a cause.
(3) Analogical hypothesis – draws analogy to explain relation.
(d) Explain the popular notion of cause.
Ans: The popular notion of cause refers to an event or factor responsible for bringing about another event, implying a cause-effect relation based on observation.
(e) Ends justify means. Explain with reference to any two cases according to Peter Singer.
Ans: According to Singer, moral actions are judged by outcomes. For example, euthanasia and animal rights can be justified if they promote maximum happiness and reduce suffering.
(f) Construct complex constructive dilemma, rebut and refute it.
Ans: Complex constructive dilemma: If taxes increase, prices rise; if taxes decrease, revenue falls. Taxes will either increase or decrease. Therefore, either prices rise or revenue falls.
Rebuttal: Alternative solutions may exist, such as balanced taxation policy that avoids both extremes.
End of Answers
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